Effects of low-lying excitations in pentalene and its derivatives in singlet fission: a model exact and density matrix renormalisation group study

Abstract

ABSTRACT Low-lying excited states in oligoquinanes, a multiple-fused five-membered ring compounds, aryl fused oligoquinanes and their derivatives are investigated within Pariser–Parr–Pople (PPP) model Hamiltonian. The calculated low-lying singlet excited states are in very good agreement with the experimental values reported in the literature. The lowest dipole allowed singlet excited state () calculated for most of the pentalene derivatives except 5,10 dihydroindolo[3,2-b]indole lies above the optically dark two-photon state resulting in the molecules to be non-fluorescent. The energy ordering of and lowest triplet energy state () for pentalene and dicyclopenta[a,e]pentalene satisfies two energy criteria for intermolecular multiexcitonic Singlet Fission (SF) process to occur.