  In recent years Polycyclic Aromatic Hydrocarbons (PAHs) have been studied for
their electronic properties as they are viewed as nanodots of graphene. They
have also been of interest as functional molecules for applications such as
light emitting diodes and solar cells. Since last few years varying structural
and chemical properties corresponding to the size and geometry of these
molecules have been studied both theoretically and experimentally. In this
paper, we carry out a systematic study of the electronic states of several PAHs
using the Pariser-Parr-Pople 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.
