Tak W. Kee

The supercontinent cycle

Publisher: Springer Science and Business Media LLC

Date: 20-04-2021

DOI: 10.1038/S43017-021-00160-0

Femtosecond Multicolor Pump−Probe Study of Ultrafast Electron Transfer of [(NH₃)₅Ru^IIINCRu^II(CN)₅]^- in Aqueous Solution

Publisher: American Chemical Society (ACS)

Date: 12-04-2002

DOI: 10.1021/JP014151F

Vibrational coherence probes the mechanism of ultrafast electron transfer in polymer–fullerene blends

Publisher: Springer Science and Business Media LLC

Date: 12-09-2014

DOI: 10.1038/NCOMMS5933

Abstract: The conversion of photoexcitations into charge carriers in organic solar cells is facilitated by the dissociation of excitons at the donor/acceptor interface. The ultrafast timescale of charge separation demands sophisticated theoretical models and raises questions about the role of coherence in the charge-transfer mechanism. Here, we apply two-dimensional electronic spectroscopy to study the electron transfer process in poly(3-hexylthiophene)/PCBM (P3HT/PCBM) blends. We report dynamics maps showing the pathways of charge transfer that clearly expose the significance of hot electron transfer. During this ultrafast electron transfer, vibrational coherence is directly transferred from the P3HT exciton to the P3HT hole polaron in the crystalline domain. This result reveals that the exciton converts to a hole with a similar spatial extent on a timescale far exceeding other photophysical dynamics including vibrational relaxation.

Controlling the Efficiency of Singlet Fission in TIPS-Pentacene/Polymer Composite Nanoparticles

Publisher: American Chemical Society (ACS)

Date: 19-02-2019

DOI: 10.1021/ACS.JPCC.8B10163

Organizing Crystalline Functionalized Pentacene Using Periodicity of Poly(Vinyl Alcohol)

Publisher: American Chemical Society (ACS)

Date: 28-12-2020

DOI: 10.1021/ACS.JPCLETT.9B03373

Abstract: Nanoparticles of acenes exhibit highly efficient intermolecular singlet fission (SF). Recent reports indicate that altering the morphology of 6,13-bis-(triisopropylsilylethynyl)pentacene (TIPS-Pn) nanoparticles has a profound influence on their SF dynamics. Here, we show that poly(vinyl alcohol) (PVA) induces a phase transition in preformed TIPS-Pn nanoparticles. These nanoparticles are amorphous when initially formed but crystalline after addition of PVA. Surface characterization indicates that a diffuse PVA layer surrounds the nanoparticles. We propose that a periodic interaction between the hydroxyl groups of PVA and TIPS groups of TIPS-Pn on the nanoparticle surface induces a large-scale structural rearrangement to yield crystalline TIPS-Pn. Such reorganization in preformed organic nanoparticles is unprecedented, and we believe that this is the first report of such an effect induced by polymer adsorption. Transient absorption spectroscopic results reveal that SF within these nanoparticles is accelerated by an order of magnitude upon structural rearrangement.

Ultrafast charge generation and relaxation dynamics in methylammonium lead bromide perovskites

Publisher: SPIE

Date: 22-12-2015

DOI: 10.1117/12.2202330

Red-Light-Mediated Photocatalytic Hydrogen Evolution by Hole Transfer from Non-Fullerene Acceptor Y6

Publisher: American Chemical Society (ACS)

Date: 23-08-2022

DOI: 10.1021/ACS.JPCC.2C05268

Optical Properties of the Atomically Precise C4 Core [Au9(PPh3)8]3+ Cluster Probed by Transient Absorption Spectroscopy and Time-Dependent Density Functional Theory

Publisher: American Chemical Society (ACS)

Date: 15-01-2021

DOI: 10.1021/ACS.JPCC.0C08838

Femtosecond Fluorescence Upconversion Investigations on the Excited-State Photophysics of Curcumin

Publisher: CSIRO Publishing

Date: 2011

DOI: 10.1071/CH10417

Abstract: The demonstration of curcumin as a photodynamic therapy agent has generated a high level of interest in understanding the photoinduced chemical and physical properties of this naturally occurring, yellow-orange medicinal compound. Important photophysical processes that may be related to photodynamic therapy effects including excited-state intramolecular hydrogen atom transfer (ESIHT) occur within the femtosecond to picosecond time scales. Femtosecond fluorescence upconversion spectroscopy has sufficient time resolution to resolve and investigate these important photophysical processes. In this review, recent advances in using femtosecond fluorescence upconversion to reveal ultrafast solvation and ESIHT of curcumin are presented. The excited-state photophysics of curcumin has been investigated in alcohols and micellar solutions. The results of curcumin in methanol and ethylene glycol reveal the presence of two decay components in the excited-state kinetics with time scales of 12–20 ps and ∼100 ps. Similarly, in a micellar solution, biphasic kinetics are present with the fast decay component having a time constant of 3–8 ps, the slow decay component 50–80 ps. Deuteration of curcumin in both media leads to a pronounced isotope effect in the slow decay component, which suggests that ESIHT is an important photophysical process on this time scale. The results of multiwavelength fluorescence upconversion studies show that the fast component in the excited-state kinetics is due to ultrafast solvation. These advances form a part of the continuing efforts to elucidate the photodynamic therapy properties of curcumin.

Formation of mantle “lone plumes” in the global downwelling zone — A multiscale modelling of subduction-controlled plume generation beneath the South China Sea

Publisher: Elsevier BV

Date: 2018

DOI: 10.1016/J.TECTO.2017.11.038

Singlet fission preserves polarisation correlation of excitons

Publisher: Royal Society of Chemistry (RSC)

Date: 2023

DOI: 10.1039/D2CP01943D

Abstract: Time-resolved polarisation anisotropy and Monte Carlo simulations show that singlet fission preserves polarisation correlation between photons absorbed and emitted by a material through removing excitons decorrelated by migration.

Optical Pumping of Poly(3-hexylthiophene) Singlet Excitons Induces Charge Carrier Generation

Publisher: American Chemical Society (ACS)

Date: 11-03-2014

DOI: 10.1021/JZ500217F

Abstract: The dynamics of high-energy excitons of poly(3-hexylthiophene) (P3HT) are shown to consist of torsional relaxation and exciton dissociation to form free carriers. In this work, we use pump-push-probe femtosecond transient absorption spectroscopy to study the highly excited states of P3HT in solution. P3HT excitons are generated using a pump pulse (400 nm) and allowed to relax to the lowest-lying excited state before re-excitation using a push pulse (900 or 1200 nm), producing high-energy excitons that decay back to the original excited state with both subpicosecond (0.16 ps) and picosecond (2.4 ps) time constants. These dynamics are consistent with P3HT torsional relaxation, with the 0.16 ps time constant assigned to ultrafast inertial torsional relaxation. Additionally, the signal exhibits an incomplete recovery, indicating dissociation of high-energy excitons to form charge carriers due to excitation by the push pulse. Our analysis indicates that charge carriers are formed with a yield of 11%.

Modeling the Inception of Supercontinent Breakup: Stress State and the Importance of Orogens

Publisher: American Geophysical Union (AGU)

Date: 11-2019

DOI: 10.1029/2019GC008538

Diamide Linked γ-Cyclodextrin Dimers as Molecular-Scale Delivery Systems for the Medicinal Pigment Curcumin to Prostate Cancer Cells

Publisher: American Chemical Society (ACS)

Date: 12-11-2013

DOI: 10.1021/MP400309S

Abstract: Diamide linked γ-cyclodextrin (γ-CD) dimers are proposed as molecular-scale delivery agents for the anticancer agent curcumin. N,N'-Bis(6(A)-deoxy-γ-cyclodextrin-6(A)-yl)succinamide (66γCD2su) and N,N'-bis(6(A)-deoxy-γ-cyclodextrin-6(A)-yl)urea (66γCD2ur) markedly suppress the degradation of curcumin by forming a strong 1:1 cooperative binding complexes. The results presented in this study describe the potential efficacy of 66γCD2su and 66γCD2ur for intracellular curcumin delivery to cancer cells. Cellular viability assays demonstrated a dose-dependent antiproliferative effect of curcumin in human prostate cancer (PC-3) cells that was preserved by the curcumin-66γCD2su complex. In contrast, delivery of curcumin by 66γCD2ur significantly delayed the antiproliferative effect. We observed similar patterns of gene regulation in PC-3 cells for curcumin complexed with either 66γCD2su or 66γCD2ur in comparison to curcumin alone, although curcumin delivered by either 66γCD2su or 66γCD2ur induces a slightly higher up-regulation of heme oxygenase-1. Highlighting their nontoxic nature, neither 66γCD2su nor 66γCD2ur carriers alone had any measurable effect on cell proliferation or candidate gene expression in PC-3 cells. Finally, confocal fluorescence imaging and uptake studies were used to demonstrate the intracellular delivery of curcumin by 66γCD2su and 66γCD2ur. Overall, these results demonstrate effective intracellular delivery and action of curcumin when complexed with 66γCD2su and 66γCD2ur, providing further evidence of their potential applications to deliver curcumin effectively in cancer and other treatment settings.

Reduction of Copper(II) to Copper(I) in the Copper-Curcumin Complex Induces Decomposition of Curcumin

Publisher: CSIRO Publishing

Date: 2012

DOI: 10.1071/CH12081

Abstract: We report the decomposition of curcumin due to reduction of Cu(ii) to Cu(i). Cu(ii) binds tightly with curcumin to form a complex which exhibits a high stability in methanol, but it decomposes readily in acetonitrile and in SDS micelles in the presence of ascorbic acid, coincident with reduction of Cu(ii) to Cu(i). In this study, the UV-Vis absorption of the Cu-curcumin complex shows a monotonic decrease as a function of time, consistent with the decomposition of curcumin. At a high copper : curcumin molar ratio of 10 : 1, the UV-Vis absorption spectrum of the Cu(ii)-curcumin complex in acetonitrile exhibits a substantial blue shift of the absorption maximum from 420 nm to 350 nm, which is indicative of a significant decrease in conjugation length of curcumin in the presence of Cu(ii). Time-dependent mass spectrometry and high performance liquid chromatography (HPLC) data are also consistent with the decomposition of curcumin as a consequence of reduction of Cu(ii) to Cu(i).

Effective Stabilization of Curcumin by Association to Plasma Proteins: Human Serum Albumin and Fibrinogen

Publisher: American Chemical Society (ACS)

Date: 25-03-2009

DOI: 10.1021/LA804215V

Abstract: The use of curcumin as an effective wound healing agent is of significant interest currently. It is well established that curcumin undergoes rapid degradation in physiological buffer by hydrolysis. The means by which curcumin is stabilized at the wound site to enable healing is poorly understood because blood plasma is composed of approximately 92% water. Plasma proteins, which constitute the remaining 6-8%, has been shown to stabilize curcumin. It is, however, still unclear which proteins are responsible for this phenomenon. In this study, the effects of major plasma proteins, which include human serum albumin (HSA), fibrinogen, immunoglobulin G (IgG), and transferrin, on stabilizing curcumin are investigated. In particular, we investigate their effects on the hydrolysis of curcumin at pH 7.4. In the presence of both transferrin and IgG, curcumin continues to undergo rapid hydrolysis but this reaction is suppressed by the presence of either HSA or fibrinogen with an impressive yield of approximately 95%. Furthermore, the binding constants of curcumin to HSA and fibrinogen are on the order of 10(4) and 10(5) M(-1), respectively. The binding constants of transferrin and IgG, however, are at least 1 order of magnitude less than those of HSA and fibrinogen. The results support that strong binding occurs at the hydrophobic moieties of HSA and fibrinogen, excluding water access. Therefore, strong interactions with HSA and fibrinogen inhibit hydrolysis of curcumin and in turn lead to effective suppression of degradation.

Femtosecond Pump–Push–Probe and Pump–Dump–Probe Spectroscopy of Conjugated Polymers: New Insight and Opportunities

Publisher: American Chemical Society (ACS)

Date: 08-09-2014

DOI: 10.1021/JZ501549H

Abstract: Conjugated polymers are an important class of soft materials that exhibit a wide range of applications. The excited states of conjugated polymers, often referred to as excitons, can either deactivate to yield the ground state or dissociate in the presence of an electron acceptor to form charge carriers. These interesting properties give rise to their luminescence and the photovoltaic effect. Femtosecond spectroscopy is a crucial tool for studying conjugated polymers. Recently, more elaborate experimental configurations utilizing three optical pulses, namely, pump-push-probe and pump-dump-probe, have been employed to investigate the properties of excitons and charge-transfer states of conjugated polymers. These studies have revealed new insight into femtosecond torsional relaxation and detrapping of bound charge pairs of conjugated polymers. This Perspective highlights (1) the recent achievements by several research groups in using pump-push-probe and pump-dump-probe spectroscopy to study conjugated polymers and (2) future opportunities and potential challenges of these techniques.

Density functional theory investigation of Cu(I)- and Cu(II)-curcumin complexes

Publisher: Wiley

Date: 20-08-2011

DOI: 10.1002/JCC.21631

Abstract: Density functional theory is used to obtain the lowest energy geometries of bis-aqua curcumin complexes and bis-curcumin complexes of Cu(I) and Cu(II). Three conformations of curcumin, obtained by rotation of the substituted aromatic groups, were considered in each case. Steric repulsion, due to the methoxy–methoxy interactions, was found to be an important factor in determining the lowest energy conformer of Cu(II)(curcumin)2 but was less important for the Cu(I) analog. Using a sufficiently large basis set, the results show that the lowest energy Cu(II)(curcumin)2 geometry is square planar around the copper atom, in contrast to the results from a previous study (Shen et al. THEOCHEM-J Mol Struct 2005, 757, 199). In addition, other studies suggested that the formation of this complex is followed by the reduction of Cu(II) to Cu(I). We also examined the singly occupied molecular orbital, spin density, and natural bond orbitals of Cu(II)(curcumin)2. While the former two analyses show little evidence of electron transfer from curcumin into the Cu center, the latter indicates that Cu(II) is partially reduced to Cu(I) as a consequence of complexation. Finally, we consider the bis-aqua curcumin and bis-curcumin complexes on a reaction path involving progressive displacement of water molecules by curcumin ligands. The results show that the bis-curcumin complex is the most stable Cu(II) complex, showing consistently exothermic steps in the reaction path. However, for Cu(I), the final step in the reaction path is essentially thermoneutral, indicating that the 1:1 and 1:2 Cu(I) complexes are equally stable thermodynamically.

Excited-state dynamics of the medicinal pigment curcumin in a hydrogel

Publisher: Royal Society of Chemistry (RSC)

Date: 2016

DOI: 10.1039/C6CP05648B

Abstract: Curcumin is a yellow polyphenol with multiple medicinal effects. We show that excited-state intramolecular hydrogen atom transfer and solvent reorganisation are major photophysical events for curcumin in the PAAC18 hydrogel.

Nanoprecipitation and Spectroscopic Characterization of Curcumin-Encapsulated Polyester Nanoparticles

Publisher: American Chemical Society (ACS)

Date: 15-10-2015

DOI: 10.1021/ACS.LANGMUIR.5B02773

Abstract: Curcumin-encapsulated polyester nanoparticles (Cur-polyester NPs) of approximately 100 nm diameter with a negatively charged surface were prepared using a one-step nanoprecipitation method. The Cur-polyester NPs were prepared using polylactic acid, poly(D,L-lactic-co-glycolic acid) and poly(ϵ-caprolactone) without any emulsifier or surfactant. The encapsulation of curcumin in these polyester NPs greatly suppresses curcumin degradation in the aqueous environment due to its segregation from water. In addition, the fluorescence of curcumin in polyester NPs has a quantum yield of 4 to 5%, which is higher than that of curcumin in micellar systems and comparable to those in organic solvents, further supporting the idea that the polyester NPs are capable of excluding water from curcumin. Furthermore, the results from femtosecond fluorescence upconversion spectroscopy reveal that there is a decrease in the signal litude corresponding to solvent reorganization of excited state curcumin in the polyester NPs compared with curcumin in micellar systems. The Cur-polyester NPs also show a lack of deuterium isotope effect in the fluorescence lifetime. These results indicate that the interaction between curcumin and water in the polyester NPs is significantly weaker than that in micelles. Therefore, the aqueous stability of curcumin is greatly improved due to highly effective segregation from water. The overall outcome suggests that the polyester NPs prepared using the method reported herein are an attractive system for encapsulating and stabilizing curcumin in the aqueous environment.

Nanoparticle Size-Dependent Singlet Fission and Exciton Dynamics in Amorphous TIPS-Pentacene

Publisher: American Chemical Society (ACS)

Date: 28-09-2021

DOI: 10.1021/ACS.JPCC.1C07048

Coarse-grained simulations of the effects of chain length, solvent quality, and chemical defects on the solution-phase morphology of MEH-PPV conjugated polymers

Publisher: CSIRO Publishing

Date: 2012

DOI: 10.1071/CH12029

Abstract: A mesoscale coarse-grained model of the conjugated polymer poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) in implicit solvent is developed. The model is parametrized to reproduce the local structure and dynamics of an atomistic simulation model and accounts for the effects of solvent quality and saturation chemical defects on the polymer structure. Polymers with defect concentrations of 0 to 10 % are simulated using Langevin dynamics in tetrahydrofuran (THF) and in a model poor solvent for chain lengths and solution concentrations used experimentally. The polymer chains are extended in THF and collapse into compact structures in the poor solvent. The radius of gyration decreases with defect content in THF and agrees quantitatively with experiment. The structures formed in poor solvent by chains with 300 monomer units change from toroidal to cylindrical with increasing defect content, while chains containing 1000 monomers form cylinders regardless of defect content. These results have implications for energy transfer in MEH-PPV.

Weak orogenic lithosphere guides the pattern of plume-triggered supercontinent break-up

Publisher: Springer Science and Business Media LLC

Date: 19-11-2020

DOI: 10.1038/S43247-020-00052-Z

Abstract: The importance of nonrigid geological features (such as orogens) inside tectonic plates on Earth’s dynamic evolution lacks thorough investigation. In particular, the influence of continent-spanning orogens on (super)continental break-up remains unclear. Here we reconstruct global orogens and model their controlling effects on Pangea break-up. We show that while loci of Pangea break-up are linked to mantle plumes, development of continental rifts is guided by orogens. Rifting at Central Atlantic is driven by the modelled plume responsible for the Central Atlantic Magmatic Province (CAMP) within Pangea-forming orogens. South Atlantic rifting is controlled by necking between Pangea- and Gondwana-forming orogens with the assistance of plume-induced lithospheric weakening. Without CAMP-induced weakening, South Atlantic rifting fails between the West African and Amazonian cratons, but occurs between the West African and Saharan cratons instead. Our modeling on Pangea break-up is able to recreate present-day continental geometry through the combined effect of orogens and plume center-locations.

Encapsulation of curcumin in cationic micelles suppresses alkaline hydrolysis

Publisher: American Chemical Society (ACS)

Date: 07-05-2008

DOI: 10.1021/LA800780W

Abstract: The alkaline hydrolysis of curcumin was studied in three types of micelles composed of the cationic surfactants cetyl trimethylammonium bromide (CTAB) and dodecyl trimethylammonium bromide (DTAB) and the anionic surfactant sodium dodecyl sulfate (SDS). At pH 13, curcumin undergoes rapid degradation by alkaline hydrolysis in the SDS micellar solution. In contrast, alkaline hydrolysis of curcumin is greatly suppressed in the presence of either CTAB or DTAB micelles, with a yield of suppression close to 90%. The results from fluorescence spectroscopic studies reveal that while curcumin remains encapsulated in CTAB and DTAB micelles at pH 13, curcumin is dissociated from the SDS micelles to the aqueous phase at this pH. The absence of encapsulation and stabilization in the SDS micellar solution results in rapid hydrolysis of curcumin.

Generation of Fluorescent and Stable Conjugated Polymer Nanoparticles with Hydrophobically Modified Poly(acrylate)s

Publisher: American Chemical Society (ACS)

Date: 10-11-2016

DOI: 10.1021/ACS.MACROMOL.6B02002

Aggregation and Host–Guest Interactions in Dansyl-Substituted Poly(acrylate)s in the Presence of β-Cyclodextrin and a β-Cyclodextrin Dimer in Aqueous Solution: A UV–Vis, Fluorescence, ¹H NM

Publisher: American Chemical Society (ACS)

Date: 22-11-2011

DOI: 10.1021/MA202055A

From light to hydrogen: the complete life cycle of free charges in organic photocatalytic nanoparticles

Publisher: American Chemical Society (ACS)

Date: 27-09-2023

DOI: 10.26434/CHEMRXIV-2023-PZWP3

Origin of the Excited-State Absorption Spectrum of Polythiophene

Publisher: American Chemical Society (ACS)

Date: 09-06-2017

DOI: 10.1021/ACS.JPCLETT.7B01053

Abstract: The excited states of conjugated polymers play a central role in their applications in organic solar photovoltaics. The delocalized excited states of conjugated polymers are short-lived (τ < 40 fs) but are imperative in the photovoltaic properties of these materials. Photoexcitation of poly(3-hexylthiophene) (P3HT) induces an excited-state absorption band, but the transitions that are involved are not well understood. In this work, calculations have been performed on P3HT analogues using nonlinear response time-dependent density functional theory to show that an increase in the oligomer length correlates with the dominance of the S

Solvation Dynamics of the Hydrated Electron Depends on Its Initial Degree of Electron Delocalization

Publisher: American Chemical Society (ACS)

Date: 23-01-2002

DOI: 10.1021/JP014291P

Pitfalls of quantifying intersystem crossing rates in singlet-fission chromophore solutions

Publisher: AIP Publishing

Date: 26-08-2022

DOI: 10.1063/5.0100619

Abstract: Singlet fission (SF), a process that produces two triplet excitons from one singlet exciton, has attracted recent interest for its potential to circumvent the detailed-balance efficiency limit of single-junction solar cells. For the potential of SF to be fully realized, accurate assignment and quantification of SF is necessary. Intersystem crossing (ISC) is another process of singlet to triplet conversion that is important to distinguish from SF to avoid either over- or under-estimation of SF triplet production. Here, we quantify an upper bound on the rate of ISC in two commonly studied SF chromophores, TIPS–pentacene and TIPS–tetracene, by using transient absorption spectroscopy of solutions of varying concentrations in toluene. We show that SF in solutions of these acenes has previously been misidentified as ISC, and vice versa. By determining a bimolecular SF rate constant in concentrated solutions in which SF dominates over ISC, we distinguish triplet formation due to SF from triplet formation due to ISC and show that the characteristic time scale of ISC must be longer than 325 ns in TIPS–pentacene, while it must be longer than 118 ns in TIPS–tetracene. We additionally note that no excimer formation is observed in the relatively dilute (up to 8 mM) solutions studied here, indicating that previous excimer formation observed at much higher concentrations may be partially due to aggregate formation. This work highlights that an accurate quantification of ISC is crucial as it leads to accurate determination of SF rate constants and yields.

The mechanism of electron–cation geminate recombination in liquid isooctane

Publisher: Elsevier BV

Date: 02-2005

DOI: 10.1016/J.CPLETT.2005.01.015

Corrigendum to “Nanosecond long excited state lifetimes observed in hafnium nitride” [Sol. Energy Mater. Sol. Cells 169 (2017) 13–18] (S0927024817302064) (10.1016/j.solmat.2017.04.037))

Publisher: Elsevier BV

Date: 11-2017

DOI: 10.1016/J.SOLMAT.2017.05.054

Second-harmonic generation and two-photon-excited autofluorescence microscopy of cardiomyocytes: Quantification of cell volume and myosin filaments

Publisher: SPIE-Intl Soc Optical Eng

Date: 2008

DOI: 10.1117/1.3027970

Abstract: The ability to quantify changes in cardiomyocyte and myosin volume across gestation and in response to intrauterine insults will lead to a better understanding of the link between low birth weight and an increased risk of heart disease in adult life. We present the use of second-harmonic generation (SHG) and two-photon excitation autofluorescence (TPEF) microscopy to image unstained isolated fetal cardiomyocytes. The simultaneous collection of these two images provides a wealth of information on the morphology of cardiomyocytes. The SHG signal provides high-contrast images of myosin filaments and the TPEF signal can be used to clearly visualize cell morphology. A potential issue may arise if SHG microscopy is performed exclusively due to the lack of sensitivity to distinguish between mononucleated and binucleated cardiomyocytes. However, TPEF microscopy has the ability to efficiently separate the two types of cardiomyocytes. In addition, quantitative analysis of the SHG and TPEF images enables quantification of myosin filament level and accurate determination of cell volume. In short, we demonstrate that advanced nonlinear optical microscopy can be used to answer key physiological questions in the early origins of adult health with increased accuracy and speed compared to previously used methods.

Coarse-grained simulations of the solution-phase self-assembly of poly(3-hexylthiophene) nanostructures

Publisher: Royal Society of Chemistry (RSC)

Date: 2013

DOI: 10.1039/C3NR33324H

Abstract: Under certain conditions the conjugated polymer poly(3-hexylthiophene) (P3HT) self-assembles into high-aspect-ratio nanostructures (known as nanofibres, nanowires, or nanoribbons) when cooled below its solubility limit in a marginal solvent such as anisole. Such nanostructures are potentially beneficial for organic photovoltaic device performance. In this work, Langevin dynamics simulations of a coarse-grained model of P3HT in implicit anisole solvent are used to study the self-assembly of P3HT nanostructures for polymer chain lengths and concentrations used experimentally to prepare P3HT nanofibres. The coarse-grained model is parametrised to match the local structure and dynamics of an atomistic model with explicit solvent. Nanofibres are also prepared experimentally and characterised by atomic force microscopy and UV-vis spectroscopy. The simulations match the experimental phase behaviour of P3HT in anisole, showing aggregation of P3HT at 293 and 308 K but not at 323 or 353 K. Single-chain simulations at 293 K reveal two distinct nano-scale aggregate morphologies: hairpins and helices. Hairpin aggregates, which are the precursors of nanofibres, are slightly favoured energetically at 293 K for nuclei of the critical size of ≈80 monomers for aggregation. Consequently, chains in multi-chain aggregates adopt the hairpin morphology exclusively in simulations at experimental concentrations at 293 K. The simulated aggregate sizes match experimentally measured nanofibre widths. An estimate of the shift in UV-vis absorption of P3HT due to the change in conjugation length with aggregation in the simulations agrees reasonably well with experiment and shows that most of the spectral red shift that occurs with nanofibre formation is due to increased planarisation of the P3HT chains. In addition to providing insight into the mechanisms of nanofibre formation, the simulations resolve details of the molecular-level organisation of chains in P3HT nanofibres hitherto inaccessible by experiment.

Molecular-Level Details of Morphology-Dependent Exciton Migration in Poly(3-hexylthiophene) Nanostructures

Publisher: American Chemical Society (ACS)

Date: 19-03-2015

DOI: 10.1021/ACS.JPCC.5B00705

Dispersion-independent terahertz classification based on Geometric Algebra for substance detection

Publisher: IEEE

Date: 09-2016

DOI: 10.1109/IRMMW-THZ.2016.7758626

Excited-State Intramolecular Hydrogen Atom Transfer and Solvation Dynamics of the Medicinal Pigment Curcumin

Publisher: American Chemical Society (ACS)

Date: 24-03-2009

DOI: 10.1021/JP901234Z

Abstract: The potential use of the naturally occurring yellow-orange pigment curcumin as a photodynamic therapy agent is one of the most exciting applications of this medicinal compound. Although subnanosecond spectroscopy has been used to investigate the photophysical processes of curcumin, the time resolution is insufficient to detect important and faster photoinduced processes, including solvation and excited-state intramolecular hydrogen atom transfer (ESIHT). In this study, the excited-state photophysics of curcumin is studied by means of ultrafast fluorescence upconversion spectroscopy. The results show two decay components in the excited-state kinetics with time scales of 12-20 ps and approximately 100 ps in methanol and ethylene glycol. The resulting prominent isotope effect in the long component upon deuteration indicates that curcumin undergoes ESIHT in these solvents. The short component (12-20 ps) is insensitive to deuteration, and multiwavelength fluorescence upconversion results show that this decay component is due to solvation of excited-state curcumin.

Femtosecond dynamics of excitons and hole-polarons in composite P3HT/PCBM nanoparticles

Publisher: American Chemical Society (ACS)

Date: 19-02-2013

DOI: 10.1021/JP308876Z

Abstract: The dynamics of charge separation in aqueous suspensions of regioregular P3HT nanoparticles containing PCBM were investigated for the first time using femtosecond transient absorption spectroscopy. This investigation is supported by the recently reported use of regioregular P3HT/PCBM nanoparticles as charge trapping and storage devices. In this study, the presence of excited-state and charge-separated species, including singlet excitons, polymer polarons and free charges, generated in rr-P3HT/PCBM nanoparticles was identified through visible pump and visible/near-infrared probe femtosecond transient absorption spectroscopy at a range of electron acceptor concentrations. The decrease of the singlet exciton lifetime by charge transfer to PCBM is well described by a one-dimensional diffusion model with a P3HT domain size of approximately 5 nm for 5-50 wt % PCBM. This model also indicates that bimolecular recombination is the dominant charge recombination mechanism at 20 wt % PCBM and above.

What Next for Singlet Fission in Photovoltaics? The Fate of Triplet and Triplet-Pair Excitons

Publisher: American Chemical Society (ACS)

Date: 22-03-2022

DOI: 10.1021/ACS.JPCC.2C00273

The Role of Charge in the Surfactant-Assisted Stabilization of the Natural Product Curcumin

Publisher: American Chemical Society (ACS)

Date: 18-11-2009

DOI: 10.1021/LA903772E

Abstract: Colloidal solutions of surfactants that form micelles or vesicles are useful for solubilizing and stabilizing hydrophobic molecules that are otherwise sparingly soluble in aqueous solutions. In this paper we investigate the use of micelles and vesicles prepared from ionic surfactants for solubilizing and stabilizing curcumin, a medicinal natural product that undergoes alkaline hydrolysis in water. We identify spectroscopic signatures to evaluate curcumin partitioning and deprotonation in surfactant mixtures containing micelles or vesicles. These spectroscopic signatures allow us to monitor the interaction of curcumin with charged surfactants over a wide range of pH values. Titration data are presented to show the pH dependence of curcumin interactions with negatively and positively charged micelles and vesicles. In solutions of cationic micelles or positively charged vesicles, strong interaction between the Cur(-1) phenoxide ion and the positively charged surfactants results in a change in the acidity of the phenolic hydrogen and a lowering of the apparent lowest pK(a) value for curcumin. In the microenvironments formed by anionic micelles or negatively charged bilayers, our data indicates that curcumin partitions as the Cur(0) species, which is stabilized by interactions with the respective surfactant aggregates, and this leads to an increase in the apparent pK(a) values. Our results may explain some of the discrepancies within the literature with respect to reported pK(a) values and the acidity of the enolic versus phenolic protons. Hydrolysis rates, quantum yields, and molar absorption coefficients are reported for curcumin in a variety of solutions.

Surfactant Effects on Hydrogen Evolution by Small Molecule Non-Fullerene Acceptor Nanoparticles

Publisher: American Chemical Society (ACS)

Date: 09-06-2022

DOI: 10.26434/CHEMRXIV-2022-8D6P7

Abstract: Organic donor:acceptor semiconductor nanoparticles (NPs) formed through the miniemul- sion method have been shown to be active photocatalysts. Here we report photocatalytic hydrogen (H2) evolution under sacrificial conditions with Pt as a co-catalyst by NPs comprising only the non-fullerene acceptor Y6, stabilized by either sodium dodecyl sulfate (SDS) or the thiophene-containing surfactant 2-(3-thienyl)ethyloxybutylsulfonate sodium salt (TEBS). Typically, changes in the photocatalytic activity of donor:acceptor NPs are associated with differences in morphology due to the use of surfactants. However, as these NPs are single-component, their photocatalytic activity has a significantly lower dependence on morphology than two-component donor:acceptor NPs. Results from ultrafast transient absorption spectroscopy show a minor difference between the photophysics of the TEBS- and SDS-stabilized Y6 NPs, with free charges present with either surfactant. The similar photophysics suggest that both TEBS- and SDS-stabilized Y6 NPs would be expected to have similar rates of H2 evolution. However, the results from photocatalysis show that Y6 NPs stabilized by TEBS have a H2 evolution rate 21 times higher than that of the SDS- stabilized NPs under broadband solar-like illumination (400–900 nm). Transmission electron microscopy images of the Y6 NPs show effective photodeposition of Pt on the surface of the TEBS-stabilized NPs. In contrast, photodeposition of Pt is inhibited when SDS is used. Furthermore, the zeta potential of the NPs is higher in magnitude when SDS is present. Hence, we hypothesize that SDS forms a dense, insulating layer on the NP surface which hinders the photodeposition of Pt and reduces the rate of H2 evolution. This insulating effect is absent for TEBS-stabilized Y6 NPs, allowing a high rate of H2 evolution. The TEBS-stabilized Y6 NPs have a H2 evolution rate higher than most single-component organic photocatalysts, signaling the potential use of the Y-series acceptors for H2 evolution in Z-scheme photocatalysis.

Delocalizing Electrons in Water with Light

Publisher: American Chemical Society (ACS)

Date: 16-08-2001

DOI: 10.1021/JP012431P

One-laser interferometric broadband coherent anti-Stokes Raman scattering

Publisher: Optica Publishing Group

Date: 2006

DOI: 10.1364/OE.14.003631

Anisotropic Triplet Exciton Diffusion in Crystalline Functionalized Pentacene

Publisher: American Chemical Society (ACS)

Date: 14-10-2020

DOI: 10.1021/ACS.JPCC.0C07608

Photoinduced trans-to-cis Isomerization of Cyclocurcumin

Publisher: American Chemical Society (ACS)

Date: 24-08-2011

DOI: 10.1021/JP200080S

Abstract: The photophysical properties of cyclocurcumin in various solvents are studied for the first time to shed light on the nonradiative processes of the parent compound, curcumin, which has a range of medicinal properties. Steady-state fluorescence and fluorescence-excitation spectra of cyclocurcumin in polar aprotic solvents are strongly dependent on excitation (λ(ex)) and emission (λ(em)) wavelength, respectively. The fluorescence quantum yield also depends on λ(ex) and increases with the viscosity of the medium. Time-resolved studies show nonexponential fluorescence decay in all solvents studied. The two fluorescence decay components of cyclocurcumin in alcohols exhibit a strong dependence on viscosity and temperature. NMR spectroscopy indicates that cyclocurcumin is entirely in the trans form with respect to the C6-C7 double bond in methanol, chloroform, and acetone. It is suggested that at least two conformational isomers about another single bond (C5-C6 or C7-C1″ or both) and that trans-to-cis isomerization about the C6-C7 double bond of these isomers provide the most likely means of rationalizing the steady-state spectra and the nonradiative decay mechanisms in both protic and aprotic polar solvents.

Ultrafast Carrier Dynamics in Methylammonium Lead Bromide Perovskite

Publisher: American Chemical Society (ACS)

Date: 02-2016

DOI: 10.1021/ACS.JPCC.5B11640

Characterization of the ultrafast spectral diffusion and vibronic coherence of TIPS-pentacene using 2D electronic spectroscopy

Publisher: AIP Publishing

Date: 07-2021

DOI: 10.1063/5.0055528

Abstract: TIPS-pentacene is a small-molecule organic semiconductor that is widely used in optoelectronic devices. It has been studied intensely owing to its ability to undergo singlet fission. In this study, we aim to develop further understanding of the coupling between the electronic and nuclear degrees of freedom of TIPS-pentacene (TIPS-Pn). We measured and analyzed the 2D electronic spectra of TIPS-Pn in solutions. Using center line slope (CLS) analysis, we characterized the frequency-fluctuation correlation function of the 0–0 vibronic transition. Strong oscillations in the CLS values were observed for up to 5 ps with a frequency of 264 cm−1, which are attributable to a large vibronic coupling with the TIPS-Pn ring-breathing vibrational mode. In addition, detailed analysis of the CLS values allowed us to retrieve two spectral diffusion lifetimes, which are attributed to the inertial and diffusive dynamics of solvent molecules. Amplitude beating analysis also uncovered couplings with another vibrational mode at 1173 cm−1. The experimental results can be described using the displaced harmonic oscillator model. By comparing the CLS values of the simulated data with the experimental CLS values, we estimated a Huang–Rhys factor of 0.1 for the ring-breathing vibrational mode. The results demonstrated how CLS analysis can be a useful method for characterizing the strength of vibronic coupling.

Femtosecond Transient Absorption Spectroscopy of the Medicinal Agent Curcumin in Diamide Linked γ-Cyclodextrin Dimers

Publisher: American Chemical Society (ACS)

Date: 02-10-2014

DOI: 10.1021/JP507272F

Abstract: Curcumin is a biologically active polyphenol and a yellow pigment extracted from turmeric. Our previous study has shown effective encapsulation of curcumin using diamide linked γ-cyclodextrin dimers, namely 66γCD2su and 66γCD2ur, through cooperative 1:1 host-guest complexation. In this study, the excited-state dynamics of curcumin complexed with either 66γCD2su or 66γCD2ur in water are investigated using femtosecond transient absorption spectroscopy. Both 66γCD2su-curcumin and 66γCD2ur-curcumin complexes in water show only an excited-state absorption (ESA) band at 530 nm without any stimulated emission (SE) signals, indicating non-radiative decays as the major relaxation pathways. The ESA dynamics of 66γCD2su-curcumin are similar to those of 66γCD2ur-curcumin, consisting of a rapid growth component and three decay components. The growth component, which has a time constant of 0.25-0.41 ps, is assigned to solvent reorganization. The relatively fast decay components with time constants of 9.3-21.8 ps show significant deuterium isotope effect, consistent with the presence of excited-state intramolecular hydrogen atom transfer (ESIHT) of curcumin. The small- litude and slow decay components may be attributed to the dynamics of complexed curcumin and molecular motions due to flexibility of 66γCD2su and 66γCD2ur. In addition, transient absorption anisotropy measurements reveal slow rotational motions of 66γCD2su-curcumin and 66γCD2ur-curcumin complexes. The overall results show that complexation in 66γCD2su and 66γCD2ur has pronounced effects on the photophysics of curcumin.

Terahertz Signal Classification Based on Geometric Algebra

Publisher: Institute of Electrical and Electronics Engineers (IEEE)

Date: 11-2016

DOI: 10.1109/TTHZ.2016.2610759

Femtosecond transient absorption spectroscopy of copper(II)-curcumin complexes

Publisher: Royal Society of Chemistry (RSC)

Date: 2012

DOI: 10.1039/C2CP40208D

Abstract: Ligand-metal interaction between curcumin and Cu(II) in methanol and sodium dodecyl sulfate (SDS) micelles was investigated using fluorescence spectroscopy and transient absorption spectroscopy. The Cu(II) ion exhibits a high efficiency in quenching the fluorescence of curcumin. By quantifying fluorescence quenching as a function of Cu(II) concentration, the complexation constants, K(1) and K(2), for the formation of the 1 : 1 and 1 : 2 Cu(II)-curcumin complexes, [Cu(II)-Cur](+) and [Cu(II)-Cur(2)], have been determined. In methanol, K(1) and K(2) are (1.33 ± 0.47) × 10(8) M(-1) and (6.79 ± 1.77) × 10(5) M(-1), respectively, whereas those in SDS micelles are (9.90 ± 1.68) × 10(5) M(-1) and (1.70 ± 0.48) × 10(6) M(-1), respectively. The transient absorption spectra of curcumin and the Cu(II)-curcumin complexes from 520 nm to 700 nm show a combination of stimulated emission and excited state absorption (ESA). However, the transient absorption signal at 500 nm corresponds to ESA exclusively. For curcumin, the ESA kinetics exhibit two rising components with time constants of 0.9 ps and 8.2 ps in methanol, and 0.5 ps and 2.5 ps in SDS micelles, which are consistent with solvation dynamics of excited state curcumin in these media. In addition, the ESA kinetics show a decay component with a time constant of 125 ps in methanol and 64 ps in SDS micelles, reflecting the excited state intramolecular hydrogen atom transfer of curcumin in these media. The ESA kinetics of the Cu(II)-curcumin complexes exhibit a sharp rise and a fast decay with a time constant of approximately 1 ps in both media due to the strong interaction between Cu(II) and curcumin.

Possible South-Dipping Mesozoic Subduction at Southern Tethys Ocean-Constrained from Global Tectonic Reconstructions and Seismic Tomography

Publisher: Springer Science and Business Media LLC

Date: 02-2023

DOI: 10.1007/S12583-021-1466-3

Nanoparticle–Size–Dependent Singlet Fission and Exciton Dynamics in Amorphous TIPS-Pentacene

Publisher: Cambridge University Press (CUP)

Date: 12-08-2021

DOI: 10.33774/CHEMRXIV-2021-RZNLZ

Abstract: Aqueous nanoparticle (NP) dispersions are commonly used as model systems for spectro- scopic study of singlet exciton fission (SF) in acenes such as 6,13-(triisopropylsilylethynyl) pentacene (TIPS-Pn). However, the potential for particle size effects to complicate interpretation of results in such model systems is generally ignored. In this work, we study amorphous TIPS-Pn NP dispersions prepared by the re-precipitation method over a range of particle sizes. Time-resolved fluorescence and femtosecond transient absorption spectroscopy show that exciton dynamics in these systems depend significantly upon particle size. Kinetic analysis reveals that SF becomes slower at smaller NP sizes, while triplet exciton decay (through both correlated triplet pair relaxation and geminate triplet-triplet annihilation) accelerates. These significant size-dependent effects are ascribed to increased morphological disorder within smaller NPs, weakening the intermolecular couplings which control SF and triplet migration. A non-radiative singlet quenching channel separate from SF is also identified, which has not been previously reported for NPs of SF-capable chromophores. This non-radiative singlet decay becomes a significant relaxation pathway at small particle sizes, substantially reducing SF yields. Interestingly, exciton kinetics in 81-nm NPs approach those of bulk amorphous TIPS-Pn, suggesting that NPs of this size or larger are likely good models for bulk TIPS-Pn. This work demonstrates that particle-size effects are significant for small NPs of SF chromophores, and must be accounted for in order to accurately model bulk materials with such NP dispersions.

Observation of Hot Carriers Existing in Ag₂S Nanoparticles and Its Implication on Solar Cell Application

Publisher: American Chemical Society (ACS)

Date: 06-05-2016

DOI: 10.1021/ACS.JPCC.6B02607

Nanoparticle–Size–Dependent Singlet Fission and Exciton Dynamics in Amorphous TIPS-Pentacene

Publisher: American Chemical Society (ACS)

Date: 12-08-2021

DOI: 10.26434/CHEMRXIV-2021-RZNLZ

Abstract: Aqueous nanoparticle (NP) dispersions are commonly used as model systems for spectro- scopic study of singlet exciton fission (SF) in acenes such as 6,13-(triisopropylsilylethynyl) pentacene (TIPS-Pn). However, the potential for particle size effects to complicate interpretation of results in such model systems is generally ignored. In this work, we study amorphous TIPS-Pn NP dispersions prepared by the re-precipitation method over a range of particle sizes. Time-resolved fluorescence and femtosecond transient absorption spectroscopy show that exciton dynamics in these systems depend significantly upon particle size. Kinetic analysis reveals that SF becomes slower at smaller NP sizes, while triplet exciton decay (through both correlated triplet pair relaxation and geminate triplet-triplet annihilation) accelerates. These significant size-dependent effects are ascribed to increased morphological disorder within smaller NPs, weakening the intermolecular couplings which control SF and triplet migration. A non-radiative singlet quenching channel separate from SF is also identified, which has not been previously reported for NPs of SF-capable chromophores. This non-radiative singlet decay becomes a significant relaxation pathway at small particle sizes, substantially reducing SF yields. Interestingly, exciton kinetics in 81-nm NPs approach those of bulk amorphous TIPS-Pn, suggesting that NPs of this size or larger are likely good models for bulk TIPS-Pn. This work demonstrates that particle-size effects are significant for small NPs of SF chromophores, and must be accounted for in order to accurately model bulk materials with such NP dispersions.

Emission Decay Pathways Sensitive to Circular Polarization of Excitation

Publisher: American Chemical Society (ACS)

Date: 24-09-2018

DOI: 10.1021/ACS.JPCC.8B07482

Red-Light-Mediated Photocatalytic Hydrogen Evolution by Hole Transfer from Non-Fullerene Acceptor Y6

Publisher: American Chemical Society (ACS)

Date: 24-05-2022

DOI: 10.26434/CHEMRXIV-2022-L4LXK

Abstract: One of the highest performing materials in organic photovoltaics is a blend of the polymer donor PM6 and non-fullerene acceptor (NFA) Y6. We report the use of 1:1 PM6:Y6 blend nanoparticles (NPs) prepared by the miniemulsion method for the photocatalytic production of hydrogen under sacrificial conditions, with a 2% mass loading of Pt co-catalyst. When pre- pared using TEBS, a thiophene-containing surfactant, these blend NPs have a desirable inter- mixed morphology. Under ≈1-sun illumination from 400 to 900 nm, hydrogen is produced at a rate of 8000 ± 400 μmol h−1 g−1, which is among the highest reported for organic photocata- lysts under similar conditions. Remarkably, this rate remains high at 5200 ± 300 μmol h−1 g−1 under 650 −900 nm excitation, where Y6 is exclusively excited, generating free charges by hole transfer from Y6 to PM6. The rate drops to 2400 ± 200 μmol h−1 g−1 at 400 −600 nm excitation, where PM6 is preferentially excited and free charges are generated from the conventional electron transfer mechanism. Additionally, external quantum efficiencies of 0.27 ± 0.08% at 405nm, 0.19 ± 0.04% at 565nm, and 0.22 ± 0.02% at 780nm were measured, indicating that this photocatalyst uses a broad region of solar spectrum to yield hydrogen from excitation of both the donor and the acceptor. Transient absorption spectroscopy results show that both hole transfer and electron transfer occur following the excitation of Y6 and PM6, respectively. This work is the first study to show that free charge generation via hole transfer is the dominant mechanism of hydrogen evolution in a donor:NFA blend. This work also highlights the potential that other donor:NFA blends may have for highly efficient green hydrogen production.

A Unified Electron Transfer Model for the Different Precursors and Excited States of the Hydrated Electron

Publisher: American Chemical Society (ACS)

Date: 25-08-2001

DOI: 10.1021/JP004516G

One-photon UV detrapping of the hydrated electron

Publisher: Elsevier BV

Date: 07-2001

DOI: 10.1016/S0009-2614(01)00167-1

Experimental and computational characterisation of an artificial light harvesting complex

Publisher: Royal Society of Chemistry (RSC)

Date: 2023

DOI: 10.1039/D2CP03858G

Abstract: The search for quantum behaviour within a BODIPY light-harvesting complex reveals coherent oscillations at 100 cm −1 and 600 cm −1 .

Cooperative Binding and Stabilization of the Medicinal Pigment Curcumin by Diamide Linked γ-Cyclodextrin Dimers: A Spectroscopic Characterization

Publisher: American Chemical Society (ACS)

Date: 31-12-2010

DOI: 10.1021/JP1096025

Abstract: Diamide linked γ-cyclodextrin (γ-CD) dimers are used to capture curcumin and suppress its decomposition in water. In this study, succinamide and urea linked γ-CD dimers joined through the C6(A) carbon on each γ-CD are used. The γ-CD dimers, 66γCD(2)su and 66γCD(2)ur, show a remarkable ability to suppress the decomposition of curcumin and extend its half-life from less than 30 min to greater than 16 h. The 1:1 association of curcumin with 66γCD(2)su and 66γCD(2)ur has high stability constants of 8.7 × 10(6) M(-1) and 2.0 × 10(6) M(-1), respectively. In addition, 2D (1)H NOESY NMR results show specific hydrogen interactions in the association of curcumin with 66γCD(2)su and 66γCD(2)ur, consistent with the cooperative binding of curcumin by both γ-CD annuli of 66γCD(2)su and 66γCD(2)ur. The interactions between curcumin in the linked γ-CD dimers and surfactant micelles were studied using fluorescence spectroscopy. While linked γ-CD dimer-bound curcumin has a negligible fluorescence quantum yield, a significant increase in fluorescence intensity (Φ(fl) > 2%) in the presence of micelles suggests that curcumin is delivered to the micelle. The overall results indicate that the diamide linked γ-CD dimers are highly promising systems for curcumin delivery in vivo due to effective curcumin stabilization.

Ultrafast transient absorption study of hot carrier dynamics in hafnium nitride and zirconium nitride

Publisher: IEEE

Date: 06-2015

DOI: 10.1109/PVSC.2015.7356012

Molecular basis of binding and stability of curcumin in diamide-linked γ-cyclodextrin dimers

Publisher: American Chemical Society (ACS)

Date: 04-10-2013

DOI: 10.1021/JP406125X

Abstract: Curcumin is a naturally occurring molecule with medicinal properties that is unstable in water, whose efficacy as a drug can potentially be enhanced by encapsulation inside a host molecule. In this work, the thermodynamics and mechanism of binding of curcumin to succinamide- and urea-linked γ-cyclodextrin (γ-CD) dimers in water are investigated by molecular dynamics simulations. The simulated binding constants of curcumin to succinamide- and urea-linked γ-CD dimers at 310 K are 11.3 × 10(6) M(-1) and 1.6 × 10(6) M(-1), respectively, matching well with previous experimental results of 8.7 × 10(6) M(-1) and 2.0 × 10(6) M(-1). The simulations reveal structural information about the encapsulation of curcumin inside the diamide-linked γ-CD dimers, with distinct qualitative differences observed for the two dimers. In particular, (1) the predominant orientation of curcumin inside the urea-linked γ-CD dimer is perpendicular to that in the succinamide-linked γ-CD dimer (2) the magnitude of the angle between the planes of the cyclodextrins is larger for the succinamide-linked γ-CD dimer and (3) curcumin exhibits greater configurational freedom inside the urea-linked γ-CD dimer. A consequence of some of these structural differences is that the dimer interior is more accessible to water in the succinamide-linked γ-CD dimer. These observations explain the higher stability and lower binding constant observed experimentally for curcumin in the urea-linked cyclodextrin γ-CD dimer compared with the succinamide-linked γ-CD dimer. More generally, the results demonstrate how stability and binding strength can be decoupled and thus separately optimized in host-guest systems used for drug delivery.

The Capture and Stabilization of Curcumin Using Hydrophobically Modified Polyacrylate Aggregates and Hydrogels

Publisher: American Chemical Society (ACS)

Date: 24-07-2014

DOI: 10.1021/JP5060205

Abstract: Hydrophobically modified polyacrylates are shown to suppress the degradation of the medicinal pigment curcumin under physiological conditions. In aqueous solution, the 3% octadecyl randomly substituted polyacrylate, PAAC18, forms micelle-like aggregates at a concentration of 1 wt %. Under both conditions, PAAC18 shows a remarkable ability to suppress the degradation of curcumin at pH 7.4 and 37 °C such that its degradation half-life is increased by 1600-2000-fold. The suppression of degradation is attributed to hydrophobic interactions between curcumin and the octadecyl substituents of PAAC18 within the micelle-like aggregates and the hydrogel, as indicated by 2D NOESY (1)H NMR spectroscopy. UV-visible absorption titration results are consistent with the interaction of curcumin with five octadecyl substituents on average, which appears to substantially exclude water and greatly decrease the curcumin degradation rate. Dynamic light scattering and zeta potential measurements show the average hydrodynamic diameters of the PAAC18 aggregates to be 0.86-1.15 μm with a negative surface charge. In contrast to the octadecyl substitution, the 3% dodecyl randomly substituted polyacrylate, PAAC12, shows a negligible effect on slowing the degradation of curcumin, consistent with the dodecyl substituents being insufficiently long to capture curcumin in a adequately hydrophobic environment. These observations indicate the potential for PAAC18 to act as a model drug delivery system.

Surfactant Effects on Hydrogen Evolution by Small-Molecule Nonfullerene Acceptor Nanoparticles

Publisher: American Chemical Society (ACS)

Date: 23-08-2022

DOI: 10.1021/ACSANM.2C02350

Two-Dimensional Electronic Spectroscopy Using Rotating Optical Flats.

Publisher: American Chemical Society (ACS)

Date: 13-01-2020

DOI: 10.1021/ACS.JPCA.0C00285

Abstract: In two-dimensional electronic spectroscopy (2DES), precise control of the arrival time of ultrashort laser pulses is critical to correlating the molecular states that are accessed in the experiment. In this work, we demonstrate a 2D electronic spectrometer design with an interferometric phase stability of ∼λ/250 at 600 nm. First, we present a new method for controlling pulse delay times based on transmission through pairs of optical flats rotated perpendicular to the beam propagation direction. Second, the calibration methods required to achieve adequate timing precision are also reported. Compared to existing designs using translating wedges, the rotating optical flats can achieve equivalent optical delay with a shorter path length in glass, reducing errors due to spectral dispersion of the broadband laser pulses used in 2DES. Our approach presents a simple, low-cost technique for multidimensional optical spectroscopy that is capable of resolving complex light-induced dynamics.

Low-Bandgap Conjugated Polymer Dots for Near-Infrared Fluorescence Imaging

Publisher: American Chemical Society (ACS)

Date: 15-08-2018

DOI: 10.1021/ACSANM.8B01014

Simple approach to one-laser, broadband coherent anti-Stokes Raman scattering microscopy

Publisher: Optica Publishing Group

Date: 12-2004

DOI: 10.1364/OL.29.002701

Abstract: Coherent anti-Stokes Raman scattering (CARS) microscopy is emerging as a powerful method for imaging materials and biological systems, partly because of its noninvasiveness and selective chemical sensitivity. However, its full potential for species-selective imaging is limited by a restricted spectral bandwidth. Recent increases in bandwidth are promising but still are not sufficient for the level of robust component discrimination that would be needed in a chemically complex milieu found, for ex le, in intracellular and extracellular environments. We demonstrate a truly broadband CARS imaging instrument that we use to acquire hyperspectral images with vibrational spectra over a bandwidth of 2500 cm(-1) with a resolution of 13 cm(-1).

Excited-State Intramolecular Hydrogen Atom Transfer of Curcumin in Surfactant Micelles

Publisher: American Chemical Society (ACS)

Date: 05-02-2010

DOI: 10.1021/JP9101527

Abstract: Femtosecond fluorescence upconversion experiments were performed on the naturally occurring medicinal pigment, curcumin, in anionic, cationic, and neutral micelles. In our studies, the micelles are composed of sodium dodecyl sulfate (SDS), dodecyl trimethyl ammonium bromide (DTAB), and triton X-100 (TX-100). We demonstrate that the excited-state kinetics of curcumin in micelles have a fast (3-8 ps) and slow (50-80 ps) component. While deuteration of curcumin has a negligible effect on the fast component, the slow component exhibits a pronounced isotope effect of approximately 1.6, indicating that micelle-captured curcumin undergoes excited-state intramolecular hydrogen atom transfer. Studies of solvation dynamics of curcumin in a 10 ps time window reveal a fast component (< or = 300 fs) followed by a 8, 6, and 3 ps component in the solvation correlation function for the TX-100, DTAB, and SDS micelles, respectively.

Liberation of Charge Carriers by Optical Pumping Excitons in Poly(3-hexylthiophene) Aggregates

Publisher: American Chemical Society (ACS)

Date: 17-01-2019

DOI: 10.1021/ACS.JPCC.9B00318

Chemical Defects in the Highly Fluorescent Conjugated Polymer Dots

Publisher: American Chemical Society (ACS)

Date: 11-11-2010

DOI: 10.1021/LA103063P

Abstract: We present strong evidence for the oxidation of conjugated polymers in the formation of conjugated polymer dots (CPdots) using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Although recent studies show that folding of the polymer chain into a compact 3D structure is involved in the formation of these nanoparticles, the process by which these intrinsically hydrophobic nanoscale particles circumvent aggregation in water is still not well understood. Zeta potential results show that these dots have a negatively charged surface at neutral pH, with a zeta potential and surface charge density of approximately -40 mV and (1.39 - 1.70) × 10(-2) C/m(2), respectively. In addition, quantitative elemental analysis of CPdots indicates that oxygen composes 7-13% of these nanoparticles. The overall results support the presence of chemical defects in forming a hydrophilic surface of CPdots. As a consequence, the charged surface contributes to inhibiting the aggregation of CPdots in water, leading to colloidal stability.

University Of Minnesota

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University Of Toronto

Location: Canada

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The University Of Texas At Austin

Location: United States of America

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University Of Minnesota

Location: United States of America

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University Of Adelaide

Location: Australia

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National Institute Of Standards And Technology

Location: United States of America

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Iowa State University

Location: United States of America

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Discovery Projects - Grant ID: DP160103797

Start Date: 12-2016

End Date: 10-2021

Amount: $372,900.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE100100149

Start Date: 2010

End Date: 12-2011

Amount: $500,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE130100158

Start Date: 2013

End Date: 12-2014

Amount: $200,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE200100051

Start Date: 2020

End Date: 05-2022

Amount: $755,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE0989747

Start Date: 08-2009

End Date: 12-2010

Amount: $400,000.00

Funder: Australian Research Council