Unraveling the T1 formation in mono-arm styrylbenzene heteroanalogues

Abstract

We present a theoretical investigation of the nonradiative relaxation dynamics associated with the low-lying excited electronic states of mono-arm styrylbenzene heteroanalogues. These molecules possess near-degenerate S 1 (bright π π ∗ ) and S 2 (dark n π ∗ ) states, enabling intersystem crossing via both states upon photoexcitation to S 1 . Singlet-triplet energy gaps and associated spin–orbit coupling parameters suggest favorable intersystem crossing via S 2 → T 5 . The nuclear wavepacket initiated at the Franck–Condon point of the receiver triplet state (T 5 ) decays rapidly to lower triplet states via accessible multiple conical intersections, indicating the ultrafast formation of T 1 in these molecules. Our findings show that these molecules would transfer energy to molecular oxygen via T 1 . • T 1 formation pathways of mono-arm styrylbenzene heteroanalogues are investigated. • TD-DFT calculations and SOC values reveal S 2 -T 5 as the triplet generating channel. • Conical intersections in the triplet manifold lead to ultrafast internal conversion.