Electronic structure and excited-state analysis of covalently bridged diphenylhexatriene dimers: a route to design intramolecular singlet fission

Abstract

In the field of inter-molecular singlet fission (x-SF) materials, 1,6-diphenyl-1,3,5-hexatriene (DPH) molecule has already been proven to be a promising candidate both in experiment and theory. Moreover, the design of isomeric intra-molecular singlet fission (iSF) with DPH dimers reported in a recent study by Millington et al., J. Am. Chem. Soc., 2023, 145, 2499–2510, showed comparatively higher triplet energies of approximately 1.5 eV as compared to oligoacenes for their appropriate inclusion in solar cell devices. This work reports the low-lying singlet and triplet excited states of six DPH dimers covalently linked by a phenylene bridge calculated within the Pariser–Parr–Pople (PPP) model Hamiltonian using the density matrix renormalization group (DMRG) technique and compared with time-dependent density functional theory (TD-DFT) results. The excited-state energy calculations and non-covalent interaction analysis of covalently linked DPH dimers strongly support the experimental observations, highlighting their potential as excellent iSF materials.