ORCID Profile
0000-0002-9101-0567
Current Organisations
Kasturba Medical College Manipal
,
Katholieke Universiteit Leuven
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Publisher: Wiley
Date: 30-09-2009
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D2NR06427H
Abstract: MACl post-treatment of MAPbI 3 nanoparticles in a mixed solvent successfully suppresses surface traps, associated with an improved PL intensity and lifetime, brighter and longer ON-states in PL blinking, and a more stable, enhanced photocurrent.
Publisher: SPIE
Date: 31-08-2006
DOI: 10.1117/12.681448
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2NR11805J
Abstract: Detailed understanding of the underlying mechanisms of surface enhanced Raman scattering (SERS) remains challenging for different experimental conditions. We report on an excitation wavelength dependent SERS of 4-aminothiophenol molecules on gold nanorings. SERS and normal Raman spectra, combined with well-characterized surface morphology, optical spectroscopy and electromagnetic (EM) field simulations of gold nanoring substrates indicate that the EM enhancement occurs at all three excitation wavelengths (532, 633 and 785 nm) employed but at short wavelengths (532 and 633 nm) charge transfer (CT) results in additional strong enhancements of particular Raman transitions. These results pave the way to further understanding the origin of the SERS mechanism.
Publisher: Elsevier BV
Date: 06-2011
Publisher: American Chemical Society (ACS)
Date: 09-2017
DOI: 10.1021/ACS.ACCOUNTS.7B00295
Abstract: Interest for functional silver clusters (Ag-CLs) has rapidly grown over years due to large advances in the field of nanoscale fabrication and materials science. The continuous development of strategies to fabricate small-scale silver clusters, together with their interesting physicochemical properties (molecule-like discrete energy levels, for ex le), make them very attractive for a wide variety of applied research fields, from biotechnology and the environmental sciences to fundamental chemistry and physics. Apart from useful catalytic properties, silver clusters (Ag
Publisher: Wiley
Date: 15-12-2009
Publisher: Walter de Gruyter GmbH
Date: 2006
Abstract: Evidence for intramolecular photoinduced electron transfer (ET) in synthetic systems consisting of a triphenylamine-perylenediimide donor-acceptor dendrimer or a triphenylamine-peryleneimide dendrimer at the ensemble and single-molecule (SM) level is presented. Moreover, for the first time a direct observation of the forward as well as the backward ET step is made in a single emitting entity. Fluctuations in the values of the rate constants for forward and backward ET were observed, induced by the local environment as well as by conformational changes of the dendrimer itself. The results obtained in a weakly coupled system can also be extended to a strongly coupled donor-acceptor system based on peryleneimide and penta-phenylene.
Publisher: Wiley
Date: 26-02-2021
Publisher: Wiley
Date: 31-08-2020
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/C9MH00500E
Abstract: The recent surge of scientific interest for lead halide perovskite semiconductors and optoelectronic devices has seen a mix of materials science sub-fields converge on the same “magical” crystal structure.
Publisher: American Chemical Society (ACS)
Date: 27-12-2016
Publisher: American Association for the Advancement of Science (AAAS)
Date: 16-08-2019
Abstract: The perovskite materials used for solar cells and light-emitting diodes (which are black in color) are generally less stable at room temperature than the electronically inactive nonperovskite phases (which are yellow in color). Steele et al. show that for CsPbI 3 , strain induced in a thin film after annealing the material to 330°C and then rapidly cooling it to room temperature kinetically trapped the black phase. Grazing-incidence wide-angle x-ray scattering revealed the crystal distortions and texture formation created by interfacial strain. Science , this issue p. 679
Publisher: American Chemical Society (ACS)
Date: 17-06-2021
Publisher: Royal Society of Chemistry (RSC)
Date: 2005
DOI: 10.1039/B509651K
Abstract: Two new peryleneimide end-capped polyphenylenes are shown to be deterministic single photon sources in PMMA films due to efficient annihilation between charge transfer states.
Publisher: Wiley
Date: 11-06-2023
Abstract: The frequency of reports utilizing synchrotron‐based grazing incident wide angle X‐ray scattering (GIWAXS) to study metal halide perovskite thin films has exploded recently, as this technique has proven invaluable for understanding several structure‐property relationships that fundamentally limit optoelectronic performance. The GIWAXS geometry and temporal resolution are also inherently compatible with in situ and operando setups (including ISOS protocols), and a relatively large halide perovskite research community has deployed GIWAXS to unravel important kinetic and dynamic features in these materials. Considering its rising popularity, the aim here is to accelerate the required learning curve for new experimentalists by clearly detailing the underlying analytical concepts which can be leveraged to maximize GIWAXS studies of polycrystalline thin films and devices. Motivated by the vast range of measurement conditions offered, together with the wide variety of compositions and structural motifs available (i.e., from single‐crystal and polycrystalline systems, to quantum dots and layered superlatices), a comprehensive framework for conducting effective GIWAXS experiments is outlined for different purposes. It is anticipated that providing a clear perspective for this topic will help elevate the quality of future GIWAXS studies—which have become routine—and provide the impetus required to develop novel GIWAXS approaches to resolve unsettled scientific questions.
Publisher: American Chemical Society (ACS)
Date: 13-08-2019
Publisher: Springer Science and Business Media LLC
Date: 06-12-2022
DOI: 10.1038/S41467-022-35255-9
Abstract: The black perovskite phase of CsPbI 3 is promising for optoelectronic applications however, it is unstable under ambient conditions, transforming within minutes into an optically inactive yellow phase, a fact that has so far prevented its widespread adoption. Here we use coarse photolithography to embed a PbI 2 -based interfacial microstructure into otherwise-unstable CsPbI 3 perovskite thin films and devices. Films fitted with a tessellating microgrid are rendered resistant to moisture-triggered decay and exhibit enhanced long-term stability of the black phase (beyond 2.5 years in a dry environment), due to increasing the phase transition energy barrier and limiting the spread of potential yellow phase formation to structurally isolated domains of the grid. This stabilizing effect is readily achieved at the device level, where unencapsulated CsPbI 3 perovskite photodetectors display ambient-stable operation. These findings provide insights into the nature of phase destabilization in emerging CsPbI 3 perovskite devices and demonstrate an effective stabilization procedure which is entirely orthogonal to existing approaches.
Publisher: American Chemical Society (ACS)
Date: 13-10-2021
Publisher: Wiley
Date: 29-04-2019
Abstract: The extraordinary properties of lead‐halide perovskite materials have spurred intense research, as they have a realistic perspective to play an important role in future photovoltaic devices. It is known that these materials undergo a number of structural phase transitions as a function of temperature that markedly alter their optical and electronic properties. The precise phase transition temperature and exact crystal structure in each phase, however, are controversially discussed in the literature. The linear thermal expansion of single crystals of APbX 3 (A = methylammonium (MA), formamidinium (FA) X = I, Br) below room temperature is measured using a high‐resolution capacitive dilatometer to determine the phase transition temperatures. For δ‐FAPbI 3 , two wide regions of negative thermal expansion below 173 and 54 K, and a cascade of sharp transitions for FAPbBr 3 that have not previously been reported are uncovered. Their respective crystal phases are identified via powder X‐ray diffraction. Moreover, it is demonstrated that transport under steady‐state illumination is considerably altered at the structural phase transition in the MA compounds. The results provide advanced insights into the evolution of the crystal structure with decreasing temperature that are essential to interpret the growing interest in investigating the electronic, optical, and photonic properties of lead‐halide perovskite materials.
Publisher: American Chemical Society (ACS)
Date: 07-2021
DOI: 10.1021/JACS.1C05046
Publisher: Wiley
Date: 22-04-2005
Abstract: Photoinduced electron transfer (ET) processes in a donor-acceptor system based on triphenylamine and perylene imide have been studied at the single-molecule (SM) and ensemble levels. The system exists as two isomers, one of which undergoes forward and reverse ET in toluene with decay constants of 3.0 and 2.2x10(9) s(-1), respectively, resulting in the dual emission of quenched and delayed fluorescence while the other isomer remains ET-inactive. The fluorescence of both isomers is heavily quenched in the more polar solvent, diethyl ether, by ET. A broad range of ET dynamics is seen at the SM level in polystryene with the two isomers nonresolvable indicating that the local nanoenvironment of the SMs varies considerably throughout the polymer matrix. Both the electronic coupling and the driving force for ET are shown to influence the ET dynamics. Many fluorescence trajectories of SMs show long periods (tens of milliseconds to seconds) where the count rate is attenuated either partly (a "dim" state) or to the background level (an "off-time"). During these periods, the reduction or interruption of emission is attributed to cycles of rapid charge separation followed by charge recombination to the ground state reducing the fluorescence quantum yield of the SM.
Publisher: Wiley
Date: 16-10-2021
Abstract: Metal halide perovskites draw increasing attention as photodetector materials due to their strong visible light absorption and resulting photocurrent. The development of efficient fabrication routes to realize high‐resolution perovskite pixel arrays is critical to enable practical devices. Herein, a dry lift‐off process to fabricate methylammonium lead iodide (MAPbI 3 ) pixels on different substrates is reported, with a resolution down to 5 μm. Accordingly, 8 × 10 photodetector arrays are fabricated on both glass and flexible polyethylene terephthalate (PET). These arrays show a sensitive photoresponse over a broad wavelength range from 320 to 760 nm. Moreover, when encapsulated by a Parylene‐C overlayer, the photodetector arrays on glass substrate show remarkable air stability, without noticeable performance loss after 10 days in ambient air, and the flexible photodetector arrays on PET substrate show excellent bending tolerance, retaining nearly 95% of the response after 170 bending cycles.
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7CC01776F
Abstract: A one-step method to form gold nanostars on a polydimethylsiloxane film is proposed for highly-sensitive SERS substrates.
Publisher: American Chemical Society (ACS)
Date: 26-03-2021
Publisher: Springer Science and Business Media LLC
Date: 19-01-2014
Abstract: Developing molecular systems with functions analogous to those of macroscopic machine components, such as rotors, gyroscopes and valves, is a long-standing goal of nanotechnology. However, macroscopic analogies go only so far in predicting function in nanoscale environments, where friction dominates over inertia. In some instances, ratchet mechanisms have been used to bias the ever-present random, thermally driven (Brownian) motion and drive molecular diffusion in desired directions. Here, we visualize the motions of surface-bound molecular rotors using defocused fluorescence imaging, and observe the transition from hindered to free Brownian rotation by tuning medium viscosity. We show that the otherwise random rotations can be biased by the polarization of the excitation light field, even though the associated optical torque is insufficient to overcome thermal fluctuations. The biased rotation is attributed instead to a fluctuating-friction mechanism in which photoexcitation of the rotor strongly inhibits its diffusion rate.
Publisher: American Chemical Society (ACS)
Date: 24-12-2008
DOI: 10.1021/JA807218E
Abstract: A simple and low-cost method to create metal-metal hybrid nanostructures possessing fairly regularly spaced "hot-spots" of surface plasmon resonances is proposed. The nanohybrid structure was prepared via self-assembly during a simple drop-casting procedure, using chemically synthesized silver nanowires and silver nanoparticles prepared in a single batch of a polyol process. Wide field illumination of these nanohybrids produced hot-spots with spacings of around 500 nm to 1 microm. The intensity of the emission/scattering from the hot-spots fluctuates over time. The proposed structure can be useful for the development of molecular-sensors or as a substrate for surface enhanced Raman/fluorescence spectroscopy.
Publisher: Elsevier BV
Date: 03-2005
Publisher: Elsevier BV
Date: 2005
Publisher: Elsevier BV
Date: 02-2022
Publisher: American Chemical Society (ACS)
Date: 31-12-2019
Publisher: Wiley
Date: 24-04-2021
Abstract: Research into organic–inorganic lead halide perovskites as photoactive material in solar cells and other electro‐optical devices has made immense progress in recent years. However, efficiency losses resulting from deep traps associated with framework defects, still limit the performance of perovskite semiconductors. Defect passivation by the incorporation of dopants, such as chloride doping in methylammonium lead iodide (MAPbI 3 ) perovskite, is stated as one of the most efficient ways to reduce trap densities. Commonly used parameters like improved photoluminescence (PL) quantum yields and extended PL lifetimes provide nonconclusive experimental evidence on trap density suppression by chloride doping. In this work, the effect of chloride doping on the crystal morphology, composition, and PL of MAPbI 3 nanocrystals is carefully investigated. Besides the anticipated enhanced PL intensity and extended PL lifetime, single‐particle PL intermittency studies reveal brighter and longer ON‐states with increasing amounts of chloride doping, which represents additional evidence of effective chloride‐induced trap passivation. These findings provide important guidelines for generating lead halide perovskite materials with significantly reduced trap densities toward the fabrication of high‐performance optoelectronic devices.
Publisher: CSIRO Publishing
Date: 2004
DOI: 10.1071/CH04133
Abstract: A novel dendrimer containing eight perylene diimide chromophores has been synthesized and studied by ensemble and single-molecule spectroscopic techniques. Photon anti-bunching (coincidence) measurements on single molecules embedded in zeonex polymer films show that the dendrimer behaves as a deterministic (triggered) single photon source with only one fluorescence photon being emitted following pulsed laser excitation, even when more than one chromophore is excited. This behaviour is due to efficient singlet–singlet annihilation being operative in this dendrimer. Preliminary results indicate that the triplet lifetime and yield for this molecule are similar to the values for a molecule containing a single perylene diimide chromophore.
Publisher: Springer Science and Business Media LLC
Date: 17-02-2015
DOI: 10.1038/NCOMMS7287
Abstract: The enhancement of molecular absorption, emission and scattering processes by coupling to surface plasmon polaritons on metallic nanoparticles is a key issue in plasmonics for applications in (bio)chemical sensing, light harvesting and photocatalysis. Nevertheless, the point spread functions for single-molecule emission near metallic nanoparticles remain difficult to characterize due to fluorophore photodegradation, background emission and scattering from the plasmonic structure. Here we overcome this problem by exciting fluorophores remotely using plasmons propagating along metallic nanowires. The experiments reveal a complex array of single-molecule fluorescence point spread functions that depend not only on nanowire dimensions but also on the position and orientation of the molecular transition dipole. This work has consequences for both single-molecule regime-sensing and super-resolution imaging involving metallic nanoparticles and opens the possibilities for fast size sorting of metallic nanoparticles, and for predicting molecular orientation and binding position on metallic nanoparticles via far-field optical imaging.
Publisher: SPIE
Date: 08-02-2007
DOI: 10.1117/12.701443
Publisher: American Chemical Society (ACS)
Date: 21-12-2006
DOI: 10.1021/JA064794E
Abstract: The time-dependent spectral properties of a rigid, extended system consisting of three pentaphenylene units end-capped with perylene monoimide were investigated in detail by femtosecond transient absorption and single photon timing measurements. In polar solvents, the molecular system shows the occurrence of photoinduced charge transfer. Upon gradually increasing the excitation power, annihilation involving two states with charge-transfer character has been observed. Quantum-chemical calculations performed on the system consisting of two pentaphenylene units end-capped with perylene monoimide strongly support the experimental data.
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2CC02453E
Abstract: Development of metal halide perovskite photocatalysts that can efficiently perform selective organic oxidations in combination with H 2 evolution at mild conditions.
Publisher: Wiley
Date: 06-01-2019
DOI: 10.1002/AJMG.A.61033
Publisher: American Chemical Society (ACS)
Date: 31-10-2006
DOI: 10.1021/JP064005F
Abstract: As it has been shown by pump-probe experiments electron injection at the interface between a dye molecule and mesoporous TiO2 proceeds with rates exceeding 1 x 10(13) s(-1). However, similar dye-TiO2 systems exhibit residual dye emission with lifetimes extending into the long nanosecond range. To address this inhomogeneity of injection rates time-correlated single photon counting microscopy was used to compare the emission behavior of dye-sensitized mesoporous films of TiO2 with that of in idual anatase nanoparticles that had undergone extensive dialysis. The sensitized films produce intense residual emission with multiexponential decay components as long as 220 ns. The channels of mesoporous films contain physisorbed and trapped dye, which is the dominant source of the emission. It is likely that the wide range of lifetimes reflects the distribution of mean free paths experienced by the loose dye molecules diffusing within the film prior to undergoing oxidative quenching. In contrast, the intensity of emission from in idual nanoparticles from which the loose dye was removed by dialysis is orders of magnitude lower. The lifetimes obtained from such particles are much shorter, with the primary component on a sub-nanosecond time scale. The presence of residual emission with a 230 ps lifetime shows that even on the surfaces of dialyzed nanoparticles there is a fraction of sensitizer molecules that do not inject electrons with the same high rate as is observed in ultrafast pump-probe experiments on films. Since the physisorbed dye was removed from these s les by dialysis, the residual emission is likely to originate from dye molecules bound to surface defects. Unusual collective emission bursts were observed in some of the measurements on sensitized nanoparticles. We attribute this behavior to stimulated emission from in idual nanocrystallites.
Publisher: American Chemical Society (ACS)
Date: 05-12-2018
Publisher: American Chemical Society (ACS)
Date: 10-2004
DOI: 10.1021/JP047804B
Publisher: American Chemical Society (ACS)
Date: 27-12-2021
DOI: 10.1021/ACS.JPCLETT.1C03668
Abstract: Sunlight is an abundant and clean energy source, the harvesting of which could make a significant contribution to society's increasing energy demands. Metal halide perovskites (MHP) have recently received attention for solar fuel generation through photocatalysis and solar-driven electrocatalysis. However, MHP photocatalysis is limited by low solar energy conversion efficiency, poor stability, and impractical reaction conditions. Compared to photocatalysis, MHP solar-driven electrocatalysis not only exhibits higher solar conversion efficiency but also is more stable when operating under practical reaction conditions. In this Perspective, we outline three leading types of MHP solar-driven electrocatalysis device technologies now in the research spotlight, namely, (1) photovoltaic-electrochemical (PV-EC), (2) photovoltaic-photoelectrochemical (PV-PEC), and (3) photoelectrochemical (PEC) approaches for solar-to-fuel reactions, including water-splitting and the CO
Publisher: American Chemical Society (ACS)
Date: 04-08-2017
Publisher: American Chemical Society (ACS)
Date: 22-05-2017
Abstract: Superconductivity and ferromagnetism are two mutually antagonistic states in condensed matter. Research on the interplay between these two competing orderings sheds light not only on the cause of various quantum phenomena in strongly correlated systems but also on the general mechanism of superconductivity. Here we report on the observation of the electronic entanglement between superconducting and ferromagnetic states in hydrogenated boron-doped nanodiamond films, which have a superconducting transition temperature T
Publisher: SPIE
Date: 22-05-2018
DOI: 10.1117/12.2316568
Publisher: Wiley
Date: 16-06-2021
Abstract: The study of luminescent silver nanoclusters confined inside porous zeolite crystal has garnered the interest of fundamental and applied nanomaterials research owing to the fascinating properties they exhibit once stabilized into small, molecule‐like clusters. Notably, such systems display a tunable optical emission (spanning nearly the entire visible range) and high luminescence quantum yields, features that are both sensitive to external stimuli and changes in the local environment of the cluster. Together, this combination of physical attributes has motivated research based on the intentional introduction of external atomic and molecular species into zeolites’ interior pore volume. In this progress report, recent discoveries which have helped to elucidate the dynamic luminescent emission properties of silver nanoclusters confined in zeolites are examined, highlighting promising efforts being made toward reaching rational design protocols for their functional synthesis. Several encouraging multicomponent systems that have allowed for the flexible regulation of the luminescence properties of the confined silver nanoclusters are brought into focus. Further, a brief up‐to‐date review of their applications is provided, ranging from efficient light‐emitting devices to sensitive (bio)sensors.
Publisher: American Chemical Society (ACS)
Date: 06-04-2022
Abstract: The development of improved catalysts capable of performing the Suzuki coupling reaction has attracted considerable attention. Recent findings have shown that the use of photoactive catalysts improves the performance, while the reaction mechanism and temperature-dependent performance of such systems are still under debate. Herein, we report Pd nanocubes/CsPbBr
Publisher: Wiley
Date: 14-12-2009
Abstract: The focusing of plasmons to obtain a strong and localized electromagnetic-field enhancement for surface-enhanced Raman scattering (SERS) is increasing the interest in using plasmonic devices as molecular sensors. In this Full Paper, we report the successful fabrication and demonstration of a solid-state plasmonic nanoslit-cavity device equipped with nanoantennas on a freestanding thin silicon membrane as a substrate for SERS. Numerical calculations predict a strong and spatially localized enhancement of the optical field in the nanoslit (6 nm in width) upon irradiation. The predicted enhancement factor of SERS was 5.3 x 10(5), localized in an area of just 6 x 1.5 nm(2). Raman spectroscopy and imaging confirm an enhancement factor of approximately 10(6) for SERS from molecules chemisorbed at the nanoslit, and demonstrate the electromagnetic-field-enhancing function of the plasmonic nanoantennas. The freestanding membrane is open on both sides of the nanoslit, offering the potential for through-slit molecular translocation studies, and opening bright new perspectives for SERS applications in real-time (bio)chemical analysis.
Publisher: American Chemical Society (ACS)
Date: 26-02-2018
Publisher: Wiley
Date: 07-01-2009
Abstract: Many of the biological processes taking place in cells are mediated by enzymatic reactions occurring in the cell membrane. Understanding interfacial enzymatic catalysis is therefore crucial to the understanding of cellular function. Unfortunately, a full picture of the overall mechanism of interfacial enzymatic catalysis, and particularly the important diffusion processes therein, remains unresolved. Herein we demonstrate that single-molecule wide-field fluorescence microscopy can yield important new information on these processes. We image phospholipase enzymes acting upon bilayers of their natural phospholipid substrate, tracking the diffusion of thousands of in idual enzymes while simultaneously visualising local structural changes to the substrate layer. We study several enzyme types with different affinities and catalytic activities towards the substrate. Analysis of the trajectories of each enzyme type allows us successfully to correlate the mobility of phospholipase with its catalytic activity at the substrate. The methods introduced herein represent a promising new approach to the study of interfacial/heterogeneous catalysis systems.
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2TC02498E
Abstract: A new perovskite-based turn-on sensor, Cs 4 PbBr 6 /FAU-Y, is designed by depositing the precursor of CsPbBr 3 on hygroscopic zeolite FAU-Y. This sensor shows an excellent fluorescence response when exposed to both low and high humidity conditions.
Publisher: American Chemical Society (ACS)
Date: 26-05-2007
DOI: 10.1021/JP072864D
Abstract: The single-molecule fluorescence blinking behavior of the organic dye Atto647N in various polymer matrixes such as Zeonex, PVK, and PVA as well as aqueous media was investigated. Fluorescence blinking with off-times in the millisecond to second time range is assigned to dye radical ions formed by photoinduced electron transfer reactions from or to the environment. In Zeonex and PVK, the measured off-time distributions show power law dependence, whereas, in PVA, no such dependence is observed. Rather, in this polymer, off-time distributions can be best fitted to monoexponential or stretched exponential functions. Furthermore, treatment of PVA s les to mild heating and low pressure greatly reduces the frequency of blinking events. We tentatively ascribe this to the removal of water pockets within the polymer film itself. Measurements of the dye immobilized in water in the presence of methylviologen, a strongly oxidizing agent, reveal simple exponential on- and off-time distributions. Thus, our data suggest that the blinking behavior of single organic molecules is sensitive to their immediate environment and, moreover, that fluorescence blinking on- and off-time distributions do not inherently and uniquely obey a power law.
Publisher: American Chemical Society (ACS)
Date: 07-08-2018
Abstract: The room-temperature charge carrier mobility and excitation-emission properties of metal halide perovskites are governed by their electronic band structures and intrinsic lattice phonon scattering mechanisms. Establishing how charge carriers interact within this scenario will have far-reaching consequences for developing high-efficiency materials for optoelectronic applications. Herein we evaluate the charge carrier scattering properties and conduction band environment of the double perovskite Cs
Publisher: American Chemical Society (ACS)
Date: 10-03-2020
Publisher: Proceedings of the National Academy of Sciences
Date: 28-10-2003
Abstract: We demonstrate measurements of the efficiency of competing Förster-type energy-transfer pathways in single bichromophoric systems by monitoring simultaneously the fluorescence intensity, fluorescence lifetime, and the number of independent emitters with time. Peryleneimide end-capped fluorene trimers, hexamers, and polymers with interchromophore distances of 3.4, 5.9, and on average 42 nm, respectively, served as bichromophoric systems. Because of different energy-transfer efficiencies, variations in the interchromophore distance enable the switching between homo-energy transfer (energy hopping), singlet-singlet annihilation, and singlet-triplet annihilation. The data suggest that similar energy-transfer pathways have to be considered in the analysis of single-molecule trajectories of donor/acceptor pairs as well as in natural and synthetic multichromophoric systems such as light-harvesting antennas, oligomeric fluorescent proteins, and dendrimers. Here we report selectively visualization of different energy-transfer pathways taking place between identical fluorophores in in idual bichromophoric molecules.
Publisher: American Chemical Society (ACS)
Date: 14-09-2020
Publisher: American Chemical Society (ACS)
Date: 29-09-2017
Publisher: IOP Publishing
Date: 31-08-2018
Publisher: American Chemical Society (ACS)
Date: 06-01-2006
DOI: 10.1021/JP055496R
Abstract: The blinking behavior of single Atto565 molecules on a glass surface is studied under air or nitrogen atmospheres using confocal microscopy. The broad distributions for both on- and off-time durations obey power law kinetics that are rationalized using a charge tunneling model. In this case, a charge is transferred from the Atto565 molecule to localized states found on the glass surface. Subsequent charge recombination by back charge tunneling from trap to Atto565 cation (i.e., dark state) restores the fluorescence. The off-time distribution is independent of excitation intensity (I), whereas the on-time distribution exhibits a power law exponent that varies with I. Two pathways have been identified to lead to the formation of the radical dark state. The first involves direct charge tunneling from the excited singlet S1 state to charge traps in the surrounding matrix, and the second requires charge ejection from the triplet T1 state after intersystem crossing from S1. Monte Carlo simulation studies complement the two-pathway model. Photobleaching curves of both single and ensemble molecules do not exhibit monoexponential decays suggesting complex bleaching dynamics arising from triplet and radical states.
Publisher: American Chemical Society (ACS)
Date: 20-01-2021
Publisher: Springer Science and Business Media LLC
Date: 29-01-2019
DOI: 10.1038/S41467-019-08326-7
Abstract: Halide perovskites possess enormous potential for various optoelectronic applications. Presently, a clear understanding of the interplay between the lattice and electronic effects is still elusive. Specifically, the weakly absorbing tail states and dual emission from perovskites are not satisfactorily described by existing theories based on the Urbach tail and reabsorption effect. Herein, through temperature-dependent and time-resolved spectroscopy on metal halide perovskite single crystals with organic or inorganic A-site cations, we confirm the existence of indirect tail states below the direct transition edge to arise from a dynamical Rashba splitting effect, caused by the PbBr 6 octahedral thermal polar distortions at elevated temperatures. This dynamic effect is distinct from the static Rashba splitting effect, caused by non-spherical A-site cations or surface induced lattice distortions. Our findings shed fresh perspectives on the electronic-lattice relations paramount for the design and optimization of emergent perovskites, revealing broad implications for light harvesting hoto-detection and light emission/lasing applications.
Publisher: AIP Publishing
Date: 04-2023
DOI: 10.1063/5.0144344
Abstract: Metal-halide perovskites (MHPs) exhibit excellent properties for application in optoelectronic devices. The bottleneck for their incorporation is the lack of long-term stability such as degradation due to external conditions (heat, light, oxygen, moisture, and mechanical stress), but the occurrence of phase transitions also affects their performance. Structural phase transitions are often influenced by phonon modes. Hence, an insight into both the structure and lattice dynamics is vital to assess the potential of MHPs. In this study, GIWAXS and Raman spectroscopy are applied, supported by density functional theory calculations, to investigate the apparent manifestation of structural phase transitions in the MHP CsPbBr3. Macroscopically, CsPbBr3 undergoes phase transitions between a cubic (α), tetragonal (β), and orthorhombic (γ) phase with decreasing temperature. However, microscopically, it has been argued that only the γ phase exists, while the other phases exist as averages over length and time scales within distinct temperature ranges. Here, direct proof is provided for this conjecture by analyzing both theoretical diffraction patterns and the evolution of the tilting angle of the PbBr6 octahedra from molecular dynamics simulations. Moreover, sound agreement between experimental and theoretical Raman spectra allowed to identify the Raman active phonon modes and to investigate their frequency as a function of temperature. As such, this work increases the understanding of the structure and lattice dynamics of CsPbBr3 and similar MHPs.
Publisher: American Chemical Society (ACS)
Date: 19-08-2019
Publisher: Elsevier BV
Date: 08-2002
Publisher: American Chemical Society (ACS)
Date: 21-08-2018
DOI: 10.1021/ACS.JPCLETT.8B01890
Abstract: The appealing luminescent properties of Ag-zeolites have been shown to be dependent on the local environment of the confined silver clusters. Herein, we shed light on the properties of Ag clusters inside hydrated Linde-type A (LTA) zeolites and relate them to the nature of the host framework when expanded and compressed by the incorporation of Li
Publisher: American Chemical Society (ACS)
Date: 23-06-2020
Abstract: Metal halide perovskites with direct band gap and strong light absorption are promising materials for harvesting solar energy however, their relatively narrow band gap limits their redox ability when used as a photocatalyst. Adding a second semiconductor component with the appropriate band structure offsets can generate a Z-scheme photocatalytic system, taking full advantage of the perovskite's intrinsic properties. In this work, we develop a direct Z-scheme photocatalyst based on formamidinium lead bromide and bismuth tungstate (FAPbBr
Publisher: American Chemical Society (ACS)
Date: 22-09-2022
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9TC04674G
Abstract: The applicability of Ag-exchanged zeolites as efficient phosphors for the development of near ultra-violet primary LEDs is described.
Publisher: Wiley
Date: 19-02-2019
Publisher: American Chemical Society (ACS)
Date: 13-12-2012
DOI: 10.1021/JP308683B
Publisher: Springer Science and Business Media LLC
Date: 04-2007
DOI: 10.1039/B617913D
Abstract: Two donor-bridge-acceptor compounds containing triphenylamine (TPA) donors and perylenemonoimide (PMI) acceptors have been studied by spectroscopic techniques and quantum chemical computation. Both systems have been observed to emit prompt and delayed fluorescence under certain conditions indicating that forward and reverse electron transfer (ET) processes can occur between the locally excited and the charge separated states. The experimental and computational results show that the TPA and PMI chromophores are better coupled by almost 50% in the meta isomers which undergo ET more readily than the para isomers. Quantum chemical calculations indicate that this unexpected situation is the result of a phenyl group on the side of the bridge being advantageously positioned in the meta isomers. This leads to more extensive delocalisation of the TPA HOMO into the bridge enhancing the total through bond electronic coupling between the TPA and PMI chromophores. The calculations also indicate a strong angle dependence of the total coupling in both isomers. The experimental results are discussed in the context of the high temperature limit of Marcus's theory of non-adiabatic ET.
Publisher: American Chemical Society (ACS)
Date: 15-04-2014
DOI: 10.1021/LA500121F
Abstract: Important cellular events such as ision require drastic changes in the shape of the membrane. These remodeling processes can be triggered by the binding of specific proteins or by changes in membrane composition and are linked to phospholipid metabolism for which dedicated enzymes, named phospholipases, are responsible. Here wide-field fluorescence microscopy is used to visualize shape changes induced by the action of phospholipase A1 on dye-labeled supported membranes of POPC (1-palmitoyl-2-oleoly-sn-glycero-3-phosphocholine). Time-lapse imaging demonstrates that layers either shrink and disappear or fold and collapse into vesicles. These vesicles can undergo further transformations such as budding, tubulation, and pearling within 5 min of formation. Using dye-labeled phospholipases, we can monitor the presence of the enzyme at specific positions on the membrane as the shape transformations occur. Furthermore, incorporating the products of hydrolysis into POPC membranes is shown to induce transformations similar to those observed for enzyme action. The results suggest that phospholipase-mediated hydrolysis plays an important role in membrane transformations by altering the membrane composition, and a model is proposed for membrane curvature based on the presence and shape of hydrolysis products.
Publisher: American Chemical Society (ACS)
Date: 06-03-2020
Publisher: Wiley
Date: 28-05-2014
Abstract: Live-cell surface-enhanced Raman spectroscopy (SERS) endoscopy is developed by using plasmonic nanowire waveguides as endoscopic probes. It is demonstrated that the probe insertion does not stress the cell. Opposed to conventional SERS endoscopy, with excitation at the hotspot within the cell, the remote excitation method yields low-background SERS spectra from specific cell compartments with minimal associated photodamage.
Publisher: American Chemical Society (ACS)
Date: 03-02-2009
DOI: 10.1021/NL8030696
Abstract: We demonstrate that focused laser excitation at the end of silver nanowires of 50-150 nm diameter excites SERS hot-spots at points of nanoparticle adsorption many micrometers along the wire due to the plasmon waveguide effect. The total SERS intensity detected at the hot-spots following wire-end excitation correlates with the known wavelength, polarization, and distance dependences of surface plasmon polariton (SPP) propagation in nanowires. The SERS spectra obtained at the hot-spots following wire-end excitation show very little background compared to when excitation occurs directly at the hot-spot, suggesting that a much smaller SERS excitation volume is achieved by remote, waveguide excitation. The ability to transfer SERS excitation over several micrometers, through a structure with a subdiffraction limit diameter, is discussed with respect to potential high-resolution SERS imaging applications.
No related grants have been discovered for Johan Hofkens.