Solvent as Electron Donor:  Donor/Acceptor Electronic Coupling Is a Dynamical Variable

Abstract

We combine analysis of measurements by femtosecond optical spectroscopy, computer simulations, and the generalized Mulliken-Hush (GMH) theory in the study of electron-transfer reactions and electron donoracceptor interactions. Our focus is on ultrafast photoinduced electron-transfer reactions from aromatic amine solvent donors to excited-state acceptors. The experimental results from femtosecond dynamical measurements fall into three categories: six coumarin acceptors reductively quenched by N,N-dimethylaniline (DMA), eight electron-donating amine solvents reductively quenching coumarin 152 (7-(dimethylamino)-4-(trifluoromethyl)-coumarin), and reductive quenching dynamics of two coumarins by DMA as a function of dilution in the nonreactive solvents toluene and chlorobenzene. Applying a combination of molecular dynamics trajectories, semiempirical quantum mechanical calculations (of the relevant adiabatic electronic states), and GMH theory to the C152/DMA photoreaction, we calculate the electron donor/acceptor interaction parameter H DA at various time frames. H DA is strongly modulated by both inner-sphere and outer-sphere nuclear dynamics, leading us to conclude that H DA must be considered as a dynamical variable.

Photoinduced Excited State Electron Transfer at Liquid/Liquid Interfaces

“…[32][33][34][35][36]47 Of particular importance is extending to the L/L interface the idea of using a solvent, such as N,N-dimethylaniline (DMA) as an electron donor. 37,[48][49][50][51] The advantage of this approach is that complications due to ion transfer across the interface and to diffusion are removed.…”

Excited-State Dynamics of Donor−Acceptor Bridged Systems Containing a Boron−Dipyrromethene Chromophore: Interplay between Charge Separation and Reorientational Motion

“…In this case, however, the situation is complicated by the fact that several solvent molecules can act as quencher, and thus the extraction of ET rate constant from the quenching rate constant is not straightforward. 25,26 We present here our investigation on covalently linked electron donor-acceptor bridged systems (DABS) that allow the interplay between reorientational motion and ET to be investigated. As shown in Figure 1, these DABS are composed of a boron dipyrromethene (BODIPY) derivative, 4,4-difluoro-1,3,5,7-tetramethyl-4-borata-3a-azonia-4a-aza-s-indacene (TMB-DY) linked in the 8-position to a dinitro-triptycene.…”

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.…”