Photoaccelerated Hole Transfer in Oligothiophene Assemblies

Abstract

A new series of mesitylene-linked oligothiophenes (nT, n is the number of thiophene units), including 2T-M, 3T-M, 4T-M, 4T-M-2T, and 4T-M-3T, was prepared to investigate the intramolecular hole transfer (HT) from the excited radical cation for the first time. The results of spectroscopic and theoretical studies indicated that mesitylene acts as a spacer minimizing the perturbation to the thiophene π-conjugation and increasing the stability of nT radical cations (nT•+). Femtosecond laser flash photolysis was applied to the FeCl3-oxidized 4T•+-M, 4T•+-M-2T, and 4T•+-M-3T. Upon 670 nm laser excitation, the transient absorption spectra of 4T•+-M showed the existence of two species as the D1 and D0hot states. The intramolecular HT processes from excited 4T•+ with the time constants of 1.6 and 0.8 ps were observed upon excitation of 4T•+-M-2T and 4T•+-M-3T, respectively. This is the first capture of such ultrafast processes with the subsequent back HT from the ground-state 2T•+ or 3T•+ in nT assemblies. The cur...