Energy redistribution dynamics in triarylamine-triarylborane containing hexaarylbenzenes.

Two hexaarylbenzenes (HAB) 1 and 2 each decorated by three triarylamines (TAA) as electron donors and three triarylboranes (TAB) as electron acceptors in a symmetric (1) and asymmetric (2) fashion as well as one model compound (3) with only one donor-acceptor pair were investigated by ultrafast transient absorption and fluorescence upconversion spectroscopy. Fluorescence anisotropy measurements revealed energy redistribution between localised, partly relaxed CT-states of the HABs 1 and 2 induced by dipole-dipole interaction with energy transfer time constants of ca. 3 ps. These results manifest symmetry breaking in the formally symmetric HAB 1 upon photoexcitation.