Intramolecular electron transfer beyond solvent control: probing sub-100 fs photoinduced electron transfer in triarylmethane lactones

摘要

Ultrafast charge separation (CS) processes in molecular systems ensureeffective transformation of the absorbed photon energy into the energy of acharge transfer (CT) state D-A. With 6-fs and sub-3-fs 1,2 electron transfer(ET) times reported for dye/semiconductor systems, the research on heteroge-neous ET has reached the low femtosecond limit. Though a number of studiesdemonstrate that the rate of intramolecular 3.4 barrierless ET reactions in so-lution can be as fast as 1013 the studies on intramolecular ET dynamics fasterthan diffusional solvation are very scarce. Exploring intramolecular ET in con-densed phase in this time domain can provide substantial insight into the initialstages of ET. Ultrafast ET is promoted by high-frequency intramolecular vibra-tional modes and by ultrafast (inertial) solvation. A better understanding of theinterplay between these two driving forces requires elaboration and explorationof D-A systems capable of undergoing ET on a sub-I00 fs time scale. Such ul-trafast ET processes with theoretically predicted kET up to 10'4 s have beenproposed and discussed by Jortner et al. 5, but until now there have been veryfew experimental reports on intramolecular ET on the time scale of single vibra-tions 6. A suitable system for such studies could be one with a CT state lyingbelow the locally excited (LE) state and being available from the latter upon ex-citation to the LE state without necessary stabilization by solvation dynamics.