ORCID Profile
0000-0002-3276-6196
Current Organisations
University of Adelaide
,
University of Sydney
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Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D3TC02133E
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.
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.
Publisher: American Chemical Society (ACS)
Date: 19-02-2019
Publisher: American Chemical Society (ACS)
Date: 28-09-2021
Publisher: American Chemical Society (ACS)
Date: 22-03-2022
Publisher: American Chemical Society (ACS)
Date: 27-05-2022
DOI: 10.26434/CHEMRXIV-2022-7JZV6
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.
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.
No related grants have been discovered for Alexandra N. Stuart.