The use of low-lying excited states of zethrene and its homologs in singlet fission within Pariser-Parr-Pople model Hamiltonian: A Density Matrix Renormalization Group study

Abstract

The low-lying excited states of zethrene, its homologs, and conjugated molecules like bis-phenaleno-indenofluorene, diaryl pentaleno diacenaphthylene and pentalenodiphenalene have been calculated using the Density Matrix Renormalization Group (DMRG) method within model Pariser-Parr-Pople(PPP) Hamiltonian. DMRG calculation shows that the energy ordering of low-lying singlet and triplet excited states of most of these molecules with 4nπ electrons satisfy two essential energetic conditions related to singlet fission (SF), a multiexcitonic process where one singlet exciton converts into two triplet excitons generating more number of charge carriers with longer lifetime enhancing the photoelectric conversion efficiency(PCE) in solar cell applications. The lowest singlet and triplet excited states calculated in DMRG are in very good agreement with experimental results in the literature. Such low-lying excitations and intermediate diradical characters of these molecules calculated through projected spin unrestricted Hartree–Fock (PUHF) method establish the fact that these molecules are potential candidates for designing SF materials.