Theoretical Studies of Skewed Spin Ladders and Polycyclic Aromatic Hydrocarbons

Abstract

This thesis is an effort to understand electronic structure and optical properties of low-dimensional conjugated molecules such as polyatomic aromatic hydrocarbons and nanoribbons composed of perylene monomers in addition to transport and magnetic properties of model conjugated systems such as ladders and junctions. we carry out a systematic study of the electronic states of several PAHs using the PPP model which incorporates long-range electron correlations. In all the molecules studied by us, we find that the 2A state is below the 1B state and hence none of them will be fluorescent in the gaseous phase. The singlet-triplet gap is more than one-half of the singlet-singlet gap in all cases and hence none of these PAHs can be candidates for improved solar cell efficiencies in a singlet fission. We discuss in detail the properties of the electronic states which include bond orders and spin densities (in triplets) of these systems