ORCID Profile
0000-0003-2365-2610
Current Organisation
UNSW Sydney
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Publisher: American Chemical Society (ACS)
Date: 04-06-2021
DOI: 10.26434/CHEMRXIV.14727708
Abstract: The exciton dynamics of 6,13-bis(triisopropylsilyl-ethynyl) pentacene is investigated to determine the role of excimer and aggregate formation in singlet fission in high concentration solutions. / br / Photoluminescence spectra were measured by excitation with the evanescent wave in total internal reflection, in order to avoid reabsorption effects. The spectra over nearly two magnitudes of concentration were near identical, with no evidence for excimer emission. Time-correlated single-photon counting measurements confirm that the fluorescence lifetime shortens with concentration, and we obtain a bimolecular rate constant of $4\\times10^9$\\,M$^{-1}$s$^{-1}$ in chloroform. The observed rate constant grows at high concentrations. This effect is modelled in terms of the hard sphere radial distribution function. / br / NMR measurements confirm that aggregation takes place with a binding constant of between 0.14 and 0.43M$^{-1}$. Transient absorption measurements are consistent with a diffusive encounter mechanism for singlet fission, with hints of more rapid singlet fission in aggregates at the highest concentration measured. / br / These data show that excimers do not play the role of an emissive intermediate in exothermic singlet fission in solution, and that while aggregation occurs at higher concentrations, the mechanism of singlet fission remains dominated by diffusive encounters. /
Publisher: American Chemical Society (ACS)
Date: 30-07-2019
Publisher: Springer International Publishing
Date: 09-09-2016
Publisher: American Chemical Society (ACS)
Date: 12-01-2017
Publisher: SPIE
Date: 05-10-2016
DOI: 10.1117/12.2236586
Publisher: American Chemical Society (ACS)
Date: 13-03-2019
DOI: 10.26434/CHEMRXIV.7834838.V1
Abstract: Here we demonstrate an upconversion composition using semiconductor nanocrystal sensitizers that employs molecular triplet states below the singlet oxygen energy. We show that, contrary to the usual expectation, the admission of oxygen enhances the intensity of upconverted light and significantly speeds up the photochemical processes involved. Further, we demonstrate photochemical upconversion from below the silicon band gap in the presence of oxygen.
Publisher: SPIE
Date: 26-09-2016
DOI: 10.1117/12.2238234
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5CP06953J
Abstract: Multichromophore perylene arrays were designed and synthesized to have extremely efficient resonance energy transfer, as confirmed by ultrafast spectroscopy.
Publisher: Wiley
Date: 17-01-2017
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5EE01713K
Abstract: Transient absorption spectroscopy reveals that the superior performance of three- versus two-phase polymer : fullerene blends is associated with hole migration from intermixed to pure polymer phases.
Publisher: American Chemical Society (ACS)
Date: 18-10-2016
Abstract: Here, a comprehensive study of the influence of polymer:fullerene mixing behavior on the performance, thin-film microstructure, photophysics, and device physics of polymer solar cells is presented. In particular, blends of the donor polymer PBDTTT-EFT with the acceptor PC
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7EE01387F
Abstract: Control of domain purity in polymer/fullerene solar cells is realised through controlling the time that an anti-solvent treatment is applied.
Publisher: American Chemical Society (ACS)
Date: 30-03-2021
DOI: 10.26434/CHEMRXIV.14331737
Abstract: The exciton dynamics of violanthrone-79 are investigated in solution and in the solid / state. In solution, the photo-prepared singlet is found to exhibit a strong ground-state bleach / and stimulated emission feature, but when sensitized in its triplet state, exhibits only a narrow / and weak ground-state bleach. As supported by density functional theory calculations, / this is explained by the triplet state having absorptions in the same region, with a similar / oscillator strength, as the ground state molecule. In solid films, the excited singlet is / found to survive only 100 ps, giving way to a long-lived transient absorption spectrum with / characteristics reminiscent of the triplet in solution. This is interpreted in terms of singlet / fission in the solid film. /
Publisher: American Chemical Society (ACS)
Date: 30-03-2021
DOI: 10.26434/CHEMRXIV.14331737.V1
Abstract: The exciton dynamics of violanthrone-79 are investigated in solution and in the solidstate. In solution, the photo-prepared singlet is found to exhibit a strong ground-state bleachand stimulated emission feature, but when sensitized in its triplet state, exhibits only a narrowand weak ground-state bleach. As supported by density functional theory calculations,this is explained by the triplet state having absorptions in the same region, with a similaroscillator strength, as the ground state molecule. In solid films, the excited singlet isfound to survive only 100 ps, giving way to a long-lived transient absorption spectrum withcharacteristics reminiscent of the triplet in solution. This is interpreted in terms of singletfission in the solid film.
Publisher: American Chemical Society (ACS)
Date: 04-06-2021
DOI: 10.26434/CHEMRXIV.14727708.V1
Abstract: The exciton dynamics of 6,13-bis(triisopropylsilyl-ethynyl) pentacene is investigated to determine the role of excimer and aggregate formation in singlet fission in high concentration solutions. Photoluminescence spectra were measured by excitation with the evanescent wave in total internal reflection, in order to avoid reabsorption effects. The spectra over nearly two magnitudes of concentration were near identical, with no evidence for excimer emission. Time-correlated single-photon counting measurements confirm that the fluorescence lifetime shortens with concentration, and we obtain a bimolecular rate constant of $4\\times10^9$\\,M$^{-1}$s$^{-1}$ in chloroform. The observed rate constant grows at high concentrations. This effect is modelled in terms of the hard sphere radial distribution function. NMR measurements confirm that aggregation takes place with a binding constant of between 0.14 and 0.43M$^{-1}$. Transient absorption measurements are consistent with a diffusive encounter mechanism for singlet fission, with hints of more rapid singlet fission in aggregates at the highest concentration measured. These data show that excimers do not play the role of an emissive intermediate in exothermic singlet fission in solution, and that while aggregation occurs at higher concentrations, the mechanism of singlet fission remains dominated by diffusive encounters.
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0SC02703K
Abstract: A series of tethered dual catalysts were developed, with catalytic investigations demonstrating that tethering enhances photocatalysis and thermally activated Ir catalysis. In addition, sequential and switchable catalytic reactivity was achieved.
Publisher: American Chemical Society (ACS)
Date: 13-03-2019
DOI: 10.26434/CHEMRXIV.7834838
Abstract: Here we demonstrate an upconversion composition using semiconductor nanocrystal sensitizers that employs molecular triplet states below the singlet oxygen energy. We show that, contrary to the usual expectation, the admission of oxygen enhances the intensity of upconverted light and significantly speeds up the photochemical processes involved. Further, we demonstrate photochemical upconversion from below the silicon band gap in the presence of oxygen. /
Publisher: American Chemical Society (ACS)
Date: 11-08-2016
DOI: 10.1021/ACS.JPCLETT.6B01185
Abstract: The nonmirror image relationship between absorption and fluorescence spectra of conjugated polymers contrasts with most organic chromophores and is widely considered a signature of interchromopohore energy funneling. We apply broad-band ultrafast fluorescence spectroscopy to resolve the evolution of fluorescence spectra for dilute solutions of conjugated oligothiophenes, where no energy transfer is possible. Fluorescence spectra evolve from a mirror image of absorption, which lacks vibronic structure, toward a spectrally narrower and vibronically structured species on the hundreds of femtosecond to early picosecond time scale. Our analysis of this fluorescence spectral evolution shows that a broad distribution of torsional conformers is driven to rapidly planarize in the excited state, including in solid films, which is supported by Raman spectroscopy and quantum chemical modeling. Our data have important implications for understanding different energy-transfer regimes that are delineated by structural relaxation.
Publisher: Wiley
Date: 10-11-2016
Abstract: Five polymer donors with distinct chemical structures and different electronic properties are surveyed in a planar and narrow-bandgap fused-ring electron acceptor (IDIC)-based organic solar cells, which exhibit power conversion efficiencies of up to 11%.
No related grants have been discovered for Shyamal Prasad.