The effects of donor–acceptor substitutions on the low lying excited states of stilbene and phenanthrene as energy harvesters: A model exact study

Abstract

The field of optoelectronic devices like organic light emitting diodes (OLEDs) is enriched with electronic structure of organic conjugated systems. The relative excited state energy ordering of the lowest transition dipole allowed excited singlet state (S1) and lowest triplet state (T1) is a deciding factor for such applications. To enhance the efficiency of the OLED devices the relative energy difference ΔST (S1−T1) in these molecules is desirable to be very small. The low-lying excited states of isomers of stilbene and phenanthrene are investigated under the influence of donor–acceptor substitution as well as rotation around central vinyl bond. Both exact diagonalization (ED) technique within the model Pariser–Parr–Pople (PPP) Hamiltonian and EOM-CCSD have been implemented for these calculations. Suitable donor–acceptor substitutions show a considerable effect on low-lying excitations over geometrical change due to rotation in these systems. Calculated excited state energies based on model Hamiltonian approach match very well with experiments over EOM-CCSD.