Formation and decay of intersystem crossing receiver triplet state in terthiophene and quaterthiophene

Experimental triplet quantum yields of terthiophene and quaterthiophene are investigated based on the combined analysis of computed energetics, spin‐orbit coupling constants, and quantum dynamics simulations. We discuss the triplet state generation via the S1‐T3 intersystem crossing pathway. Initial Franck–Condon conditions are employed while performing the wavepacket dynamics in the triplet manifold. The wavepacket evolving on T3 state exhibits a similar electronic population decay profile in both molecules. Finally, we illustrate how the triplet quantum yield quantity depends on the two processes: the triplet state formation and its decay. We explore the triplet state formation and its decay in terthiophene and quaterthiophene to provide a theoretical description of size‐dependent triplet quantum yields. Model vibronic Hamiltonians are employed to compute potential energy surfaces of energetically low‐lying singlet and triplet states of these molecules. Energetics, spin‐orbit coupling parameters and time‐dependent observables obtained from quantum nuclear wavepacket simulations suggest an efficient triplet generation via the higher triplet excited states in these molecules. ​