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) material, 1,6diphenyl-1,3,5-hexatriene (DPH) molecule has already been proven to be a promising candidate both in experiment and theory. Moreover, designing of isomeric intra-molecular singlet fission (iSF) with DPH dimers reported in recent experiment by Millington et al. (J. Am. Chem. Soc. 2023, 145, 2499-2510) shows 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 Pariser-Parr-Pople (PPP) model Hamiltonian using 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.