Photoinduced electron transfer and geminate recombination for photoexcited acceptors in a pure donor solvent

Abstract

Photoinduced electron transfer and geminate recombination are studied for the systems rhodamine 3B (R3B(+)) and rhodamine 6G (R6G(+)), which are cations, in neat neutral N,N-dimethylaniline (DMA). Following photoexcitation of R3B(+) or R6G(+) (abbreviated as R(+)), an electron is transferred from DMA to give the neutral radical R and the cation DMA(+). Because the DMA hole acceptor is the neat solvent, the forward transfer rate is very large, approximately 5x10(12) s(-1). The forward transfer is followed by geminate recombination, which displays a long-lived component suggesting several percent of the radicals escape geminate recombination. Spectrally resolved pump-probe experiments are used in which the probe is a "white" light continuum, and the full time-dependent spectrum is recorded with a spectrometer/charge-coupled device. Observations of stimulated emission (excited state decay-forward electron transfer), the R neutral radical spectrum, and the DMA(+) radical cation spectrum as well as the ground-state bleach recovery (geminate recombination) make it possible to unambiguously follow the electron transfer kinetics. Theoretical modeling shows that the long-lived component can be explained without invoking hole hopping or spin-forbidden transitions.

Photoinduced electron transfer and geminate recombination in the group head region of micelles

“…20 A detailed statistical mechanics theoretical model for photoinduced forward electron transfer 21,22 and the combined problem of forward transfer and geminate recombination in liquids has been tested and applied to the analysis of experiments. [23][24][25][26][27][28][29][30][31][32][33] The forward transfer/geminate recombination theory calculates the decay curves for the excited states and the radical species in a system of diffusing donors and acceptors. The theory accounts for the effect of solvent molecules on the distribution of acceptors around the donor ͑radial distribution function͒, as well as the effect of solvent molecules on the donor/acceptor diffusion coefficients at close approach ͑hydrodynamic effect 34,35 ͒.…”

Binding of the ionic liquid cation 1-alkyl-3-methylimidazolium to p-tetranitrocalix[4]arene probed by fluorescent indicator displacement

“…4). The reduction is due to the [1⋅AO] adduct formation whereby the close proximity of the four adjacent NO 2 groups on the calix [4] arene framework serves to quench the AO fluorescence [20][21][22][23][24]. Notably, AO quenching at low NO 2 group concentrations is usually insignificant, as evidenced by no statistically meaningful quenching in the presence of as high as Fig.…”

“…First, the fluorescence intensity of AO in the absence of [bmim][BF 4 ] is lower within the solution containing 1 as compared to that containing 2. This is attributed to the welldocumented fluorescence quenching nature of the nitro (NO 2 ) functionality of 1; CH 3 NO 2 and C 6 H 5 NO 2 are well-known electron/charge acceptor quenching agents[20][21][22][23]. Second, for AO in the presence of 1, a clear increase in the fluorescence intensity of AO is observed as the [bmim][BF 4 ] concentration increases.…”

Reactivity and Dynamics at Liquid Interfaces

“…[566][567][568][569][570]582 Of particular importance is extending the idea of employing solvent (typically N,N-dimethylaniline or DMA) as an electron donor to the liquid/liquid interface. 571,[583][584][585] The advantage of this approach is that complications due to ion transfer across the interface and to diffusion are obviated. Several studies of ET between coumarin dyes and electron-donating solvents in micelles, reverse micelles, at the surface of proteins and in nanocavities have demonstrated ultrafast electron transfer that is faster than solvation due to the close proximity of the redox pair.…”