Photophysics of bis(p-N,N-dimethylamino)benzylidene acetone: Does photoinduced electron transfer occur from a twisted excited state?

1989 ◽  
Vol 67 (10) ◽  
pp. 1565-1575 ◽  
Author(s):  
R. J. DeVoe ◽  
M. R. V. Sahyun ◽  
E. Schmidt ◽  
Mahin Sadrai ◽  
N. Serpone ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Transient Absorption ◽  
Polar Solvent ◽  
Transient Absorption Spectroscopy ◽  
Triplet States ◽  
Polar Solvents ◽  
Excited Species ◽  
A Charge ◽  
Franck Condon ◽  
Sequential Formation

Photoexcitation of the title compound (DMBA) in polar solvents leads to sequential formation of at least three excited species as detected by laser transient absorption spectroscopy: the lowest Franck–Condon singlet, a twisted singlet (P-state), and the lowest triplet states. Only the initially formed, localized singlet is emissive under our conditions. Interystem crossing to triplet occurs primarily from the twisted P-state in acetonitrile and in methanol. Photo-CIDNP and quantum yield measurements indicate that electron transfer occurs exclusively from the triplet in acetonitrile or methanol to sensitize decomposition of diphenyliodonium cation and to bleach DMBA. Analysis of the photochemistry is complicated by formation of a charge transfer complex of enhanced photolability. Using tris(trichloromethyl)-sym-triazine as the electron acceptor in hydrocarbon solvent, bleaching of DMBA again occurs, somewhat more efficiently than with the 'onium salt in polar solvent. We infer that under these conditions electron transfer occurs from the P-state. Keywords: photochemistry, fluorescence, electron transfer, TICT, chalcone.

scholarly journals The role of spin in the degradation of organic photovoltaics

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Ivan Ramirez ◽  
Alberto Privitera ◽  
Safakath Karuthedath ◽  
Anna Jungbluth ◽  
Johannes Benduhn ◽  
...  
Keyword(s):  
Transient Absorption ◽  
Bulk Heterojunction ◽  
Critical Factor ◽  
Model Systems ◽  
Transient Absorption Spectroscopy ◽  
Triplet States ◽  
Paramagnetic Resonance ◽  
Time Resolved ◽  
A Charge

AbstractStability is now a critical factor in the commercialization of organic photovoltaic (OPV) devices. Both extrinsic stability to oxygen and water and intrinsic stability to light and heat in inert conditions must be achieved. Triplet states are known to be problematic in both cases, leading to singlet oxygen production or fullerene dimerization. The latter is thought to proceed from unquenched singlet excitons that have undergone intersystem crossing (ISC). Instead, we show that in bulk heterojunction (BHJ) solar cells the photo-degradation of C60 via photo-oligomerization occurs primarily via back-hole transfer (BHT) from a charge-transfer state to a C60 excited triplet state. We demonstrate this to be the principal pathway from a combination of steady-state optoelectronic measurements, time-resolved electron paramagnetic resonance, and temperature-dependent transient absorption spectroscopy on model systems. BHT is a much more serious concern than ISC because it cannot be mitigated by improved exciton quenching, obtained for example by a finer BHJ morphology. As BHT is not specific to fullerenes, our results suggest that the role of electron and hole back transfer in the degradation of BHJs should also be carefully considered when designing stable OPV devices.

A Simple Dyad Exhibiting Microsecond Charge-Separation in Non-Polar Solvents

2006 ◽  
Vol 59 (3) ◽  
pp. 179 ◽  
Author(s):  
Kenneth P. Ghiggino ◽  
James A. Hutchison ◽  
Steven J. Langford ◽  
Melissa J. Latter ◽  
Marcia A.-P. Lee ◽  
...  
Keyword(s):  
Electron Spin ◽  
Charge Separation ◽  
Transient Absorption ◽  
Transient Absorption Spectroscopy ◽  
Time Resolved Fluorescence ◽  
Polar Solvents ◽  
Separation Processes ◽  
Time Resolved ◽  
A Charge

A simple photovoltaic device in which two chromophoric components are assembled by Zn–N coordination yields a charge-separated state with microsecond lifetime upon photoexcitation in non-polar solvents. Characterization of the electron transfer dynamics using time-resolved fluorescence and transient absorption spectroscopy suggests that the unusual longevity is due to charge recombination occurring between states with different electron spin character. Control of electron spin may provide a novel paradigm for optimizing light-induced charge-separation processes.

Photoinduced electron transfer from triplet states of phthalocyanines to fullerenes studied by transient absorption spectroscopies in visible and near-IR regions

2000 ◽  
Vol 04 (08) ◽  
pp. 713-721 ◽  
Author(s):  
MOHAMED E. EL-KHOULY ◽  
SHAFIQUL D.-M. ISLAM ◽  
MAMORU FUJITSUKA ◽  
OSAMU ITO
Keyword(s):  
Electron Transfer ◽  
Photoinduced Electron Transfer ◽  
Transient Absorption ◽  
Triplet States ◽  
Absorption Bands ◽  
Polar Solvents ◽  
Transfer Processes ◽  
Near Ir ◽  
Electron Transfer Processes ◽  
Electron Ejection

Photoinduced electron transfer processes between C 60/ C 70 and phthalocyanines such as tetra-tert-butylphthalocyanine ( H 2 TBPc ) and its zinc derivative ( ZnTBPc ) in polar solvents have been studied by observing the transient absorption spectra in the visible and near-IR regions. Upon predominant excitation of TBPcs with a 670 nm laser pulse in polar solvents, growth of the transient absorption bands of [Formula: see text] and [Formula: see text] was observed, accompanied by a concurrent decay of the triplet states of TBPcs (3 TBPc *). Thus it is confirmed that electron transfer occurs via 3 TBPc * in polar solvents. The electron transfer rate constants and efficiencies of electron transfer via 3 ZnTBPc * are greater than those via 3 H 2 TBPc * owing to the electron ejection ability of 3 ZnTBPc *. Solvent effects on the forward and backward electron transfer processes have been evaluated.

scholarly journals Tracking excited state decay mechanisms of pyrimidine nucleosides in real time

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Rocío Borrego-Varillas ◽  
Artur Nenov ◽  
Piotr Kabaciński ◽  
Irene Conti ◽  
Lucia Ganzer ◽  
...  
Keyword(s):  
Excited State ◽  
Transient Absorption ◽  
Building Blocks ◽  
Transient Absorption Spectroscopy ◽  
Classical Dynamics ◽  
Spectral Signatures ◽  
Spectral Signal ◽  
Order Of Magnitude ◽  
Franck Condon ◽  
Intense Debate

AbstractDNA owes its remarkable photostability to its building blocks—the nucleosides—that efficiently dissipate the energy acquired upon ultraviolet light absorption. The mechanism occurring on a sub-picosecond time scale has been a matter of intense debate. Here we combine sub-30-fs transient absorption spectroscopy experiments with broad spectral coverage and state-of-the-art mixed quantum-classical dynamics with spectral signal simulations to resolve the early steps of the deactivation mechanisms of uridine (Urd) and 5-methyluridine (5mUrd) in aqueous solution. We track the wave packet motion from the Franck-Condon region to the conical intersections (CIs) with the ground state and observe spectral signatures of excited-state vibrational modes. 5mUrd exhibits an order of magnitude longer lifetime with respect to Urd due to the solvent reorganization needed to facilitate bulky methyl group motions leading to the CI. This activates potentially lesion-inducing dynamics such as ring opening. Involvement of the 1nπ* state is found to be negligible.

Photoinduced electron transfer dynamics in dye-sensitized ZnO nanowire photoanodes

2018 ◽  
Vol 32 (19) ◽  
pp. 1840049
Author(s):  
Akihiro Furube ◽  
Takahiro Arai ◽  
Masahiro Okazaki ◽  
Shinichiro Yanagiya ◽  
Liang-Yih Chen ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Transient Absorption ◽  
Low Cost ◽  
Transient Absorption Spectroscopy ◽  
Zno Nanowire ◽  
Dye Sensitized ◽  
Femtosecond Transient Absorption ◽  
State Formula ◽  
Flexible Solar Cell

A photoanode using dye-sensitized ZnO nanowire (NW) is a good candidate for low-cost, colorful, light-weight and flexible solar cell material. We have synthesized a ZnO NW anode and a ZnO nanowire–nanoparticle (NWNP) anode, in which ZnO nanoparticles (NPs) are decollated on the surface of NWs. Photo-induced electron transfer dynamics from the excited state of sensitizer dye (D149) to the conduction band of ZnO NW and ZnO NWNP was clarified using femtosecond transient absorption spectroscopy. The decay of the single excited state ([Formula: see text]) of D149 was faster in ZnO NW than that of ZnO NWNP, indicating that NW is more suitable as an efficient electron acceptor.

Transient Absorption Spectroscopy of the Electron Transfer Step in the Photochemically Activated Polymerizations of N-ethylcarbazole and 9-phenylcarbazole.

2021 ◽  
Author(s):  
Georgia Thornton ◽  
Ryan Phelps ◽  
Andrew Orr-Ewing
Keyword(s):  
Electron Transfer ◽  
Radical Cation ◽  
Absorption Spectroscopy ◽  
Electron Acceptor ◽  
Transient Absorption ◽  
Transient Absorption Spectroscopy ◽  
Transfer Step

The polymerization of photoexcited N-ethylcarbazole (N-EC) in the presence of an electron acceptor begins with an electron transfer (ET) step to generate a radical cation of N-EC (N-EC+.). Here, the...

Trace analysis by transient absorption spectroscopy: estimation of the solubility of C60 in polar solvents

2004 ◽  
Vol 394 (1-3) ◽  
pp. 161-164 ◽  
Author(s):  
Toshitada Yoshihara ◽  
Miki Murai ◽  
Yoshiaki Tamaki ◽  
Akihiro Furube ◽  
Ryuzi Katoh
Keyword(s):  
Absorption Spectroscopy ◽  
Trace Analysis ◽  
Transient Absorption ◽  
Transient Absorption Spectroscopy ◽  
Polar Solvents

scholarly journals Charge Accumulation Kinetics in Multi-redox Molecular Catalysts Immobilised on TiO2

2020 ◽  
Author(s):  
Carlota Bozal-Ginesta ◽  
Camilo A. Mesa ◽  
Annika Eisenschmidt ◽  
Ravi Shankar ◽  
Laia Francàs ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Transient Absorption ◽  
Transient Absorption Spectroscopy ◽  
Redox Potentials ◽  
Charge Accumulation ◽  
Excitation Light ◽  
Molecular Catalyst ◽  
Hole Scavenger ◽  
Accumulation Kinetics ◽  
Molecular Catalysts

Multi-redox catalysis requires the transfer of more than one charge carrier and is crucial for solar energy conversion into fuels and valuable chemicals. In photo(electro)chemical systems, however, the necessary accumulation of multiple, long-lived charges is challenged by recombination with their counterparts. Herein, we investigate charge accumulation in two model multi-redox molecular catalysts for proton and CO<sub>2</sub> reduction attached onto mesoporous TiO<sub>2</sub> electrodes. Transient absorption spectroscopy and spectroelectrochemical techniques have been employed to study the kinetics of photoinduced electron transfer from the TiO<sub>2</sub> to the molecular catalysts in acetonitrile, with triethanolamine as the hole scavenger. At high light intensities, we detect charge accumulation in the millisecond timescale in the form of multi-reduced species. The redox potentials of the catalysts and the capacity of TiO<sub>2</sub> to accumulate electrons play an essential role in the charge accumulation process at the molecular catalyst. Recombination of reduced species with valence band holes in TiO<sub>2</sub> is observed to be faster than microseconds, while electron transfer from multi-reduced species to the conduction band or the electrolyte occurs in the millisecond timescale. Finally, under light irradiation, we show how charge accumulation on the catalyst is regulated as a function of the applied bias and the excitation light intensity.

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