Conformational Relaxation and Thermally Activated Delayed Fluorescence in Anthraquinone-Based Intramolecular Charge-Transfer Compound

Abstract

A novel donor-π-acceptor-π-donor-type (D-π-A-π-D-type) chromophore, 2,6-bis[4-(diphenylamino)phenyl]-9,10-anthraquinone (AQ(PhDPA)2), has been reported as an efficient red thermally activated delayed fluorescence (TADF) emitter. Molecular structure and conformation, which directly determine the nature of excited states of a TADF emitter, are critical for obtaining efficient reverse intersystem crossing (rISC) and TADF. In this work, a series of excited-state deactivation processes of AQ(PhDPA)2, from the optical excitation to fluorescence and TADF emitting, have been investigated by theoretical calculations and ultrafast transient absorption (TA) spectroscopy. Theoretical calculations and steady-state spectra suggest that the TADF emitter appears to have conformational twisting in the excited state. Both the relaxed S0 and S1 conformations have a small energy difference between the lowest singlet and triplet excited states (ΔEST) in favor of rISC, whereas ΔEST increases at the relaxed T1 conformation. Ult...