Systematical study on the electronic properties of monoazaphenanthrene compounds by theoretical calculations and experimental observations

Phenanthrene, the smallest phenacene molecule, has attracted attention since its discovery more than a century ago. Its mono-aza derivatives are also historical compounds and the best candidates for examining the effect of nitrogen atoms on the electronic structure. We used density functional theory to investigate the electronic properties of phenanthrene and a series of its mono-aza derivatives. The results of these calculations were discussed in compariton with experimental observations such as infrared spectra, absorption and emission spectra, and cyclic voltammograms. The two low-lying pi pi* excited states of phenanthrene are discussed on the basis of the L-b and L-a states under Platt's nomenclature. Upon cursory inspection, similar assignments appeared to apply to the excited states of the monoazaphenanthrene compounds; however, the transition dipole moment indicated that simple assignments could not be applied to these compounds. Of the five mono-aza derivatives, benz isoquinoline was an exception, and simple assignments could be applied.