Polyacenes electronic properties and their dependence on molecular size

The closed shell singlet electronic energies, atomization energies, polarizabilities, rotational constants and geometrical parameters of linear and angular (zigzag) polyacenes have been calculated employing HF and two DFT methods (B3LYP and LSDA) in conjunction with 6-31G(d) basis set. The possible linear and asymptotic relations of molecular properties of polyacene versus number of benzene rings as well as versus total number of electrons have been investigated. It was shown that the total electronic energies, atomization energies and some components of the polarizability tensor (αMM and αNN) linearly increase with the number of ring and number of electrons. Also, it was found that the rotational constants and geometrical parameters of polyacenes with asymptotic trend go toward plateau values. By extrapolation of linear and asymptotic trends of polyacenes' molecular properties we can in principle predict the properties of unknown species from those of subset of smaller polyacenes. Since computational studies are not feasible for large polyacenes, this finding makes it possible to consider molecular properties of larger polyacenes at higher level computational methods.