Energy ordering of singlet and triplet excited states in indacenodithiophene and indenofluorenes molecules in singlet fission: A model exact and density matrix renormalization group study

Abstract

Energy ordering of lowest singlet (S1) and triplet excited state (T1) dominates the optoelectronic properties of conjugated molecules. The small magnitude of S1-T1 (ΔEST) is favourable for designing efficient organic light-emitting diodes (OLEDs). Moreover, basic energy criteria E(T1)/E(S1) ⩽ 0.5 ensures singlet fission (SF) process to occur enhancing the efficiency of photovoltaic devices. The low-lying singlet and triplet excited state calculations are carried out for S-indacene, indacenodithiophene derivatives and indenofluorene homologs within Pariser-Parr-Pople model Hamiltonian using exact diagonalization and Density Matrix Renormalization Group (DMRG) techniques. S-indaceno[1,2-b:5,6-b′] dithiophene, diethno-s-indaceno dithiophene, indeno[1,2-b]fluorene are found to show a significant promise in designing novel SF materials.