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. GRAPHICAL ABSTRACT