Theoretical Study Of Photo-physical Processes And Intramolecular Charge Transfer In Indole Derivatives

We have proposed a nonadiabatic transition state theory for the study of charge transfer. Then, we investigated the photo-physical properties and intra-molecular charge transfer processes in indolylmaleimide derivatives and2-arylsubstituted indoles derivatives, employing the multi-reference second order perturbation theory (CASPT2).From a viewpoint of chemical structure, there should be an intra-molecular charge transfer process in indolylmaleimide derivatives, since the indole and maleimide moieties are good electron donor and acceptor, respectively. In indolylmaleimide, the whole molecule has a big conjugated π system, a channel for intra-molecular charge transfer, covered from indole to maleimide moieties. There are large stokes shift for most of those derivatives in our theoretical results. The large Stokes shift comes from not only the twisting induced charge transfer but also the avoided curve crossings in the excited states. Meanwhile, we have observed the optical intra-molecular charge transfer. Finally, comparing with the absorption and fluorescence measured by experiment, we have suggested that the monovalent anions by a deprotonation of the indole NH end are the most feasible species in acetonitrile.On the other hand, it is found that the fluorescence intensities of2-aryl substituted indole derivatives are much larger than those of the other indole derivatives. We thus further investigate the photo-physical processes in these compounds. Comparing to the absorption and fluorescence measured by the experiment, we have suggested that the anions by the deprotonation of indole NH end are the most feasible compounds in the solution. The intensity decreasing of the absorptions and fluorescence from2-phenylindole,2-naphthylindole to2-anthracenylindole, observed in the solution, are successful explained from the oscillator strength calculations of their anions.