Theoretical investigation and correlation of molecular parameters of polycyclic aromatic hydrocarbons

The first part of the theoretical investigation is an interpretation of the calculated singlet π,π* electronic transitions of five pentacyclic aromatic hydrocarbon molecules in terms of composite system approximations to these molecules. This study is motivated by the experimental observation that the electronic transitions of some pentacyclic aromatic hydrocarbons may be, on the basis of extinction coefficients, vibrational structure, and general band shape, correlated with the transitions of tetracyclic aromatic hydrocarbons contained within the structure of the pentacyclic. The molecules studied are benz(a)napthacene, benzo(b)chrysene, dibenzo(b,g)phenanthrene, dibenz(a,c)-anthracene, and 3,4-benzopyrene. In this "molecules in molecule" investigation, the electronic transitions of the five pentacyclic aromatic hydrocarbons are first calculated using the semi-empirical SCFMO method with limited configuration interaction. Composite system models or approximations are formed for each pentacyclic hydrocarbon by conceptually breaking certain pairs of bonds in the subject molecule. The electronic transitions of these composite systems are then calculated. The electronic transitions of each subject pentacyclic hydrocarbon are next correlated to the transitions of the composite system model whose transitions most closely approximate those of the subject molecule. [...]