Excited state dipole moments of nitrobenzene derivatives
Abstract
The excited state dipole moments of a series of m- and p-nitrobenzene derivatives of type A–Ph–D have been evaluated from absorption spectra measurements (in the vapour and in solution) by employing various solvent shift equations, and by semiempirical MO methods (MIM and PPP). The µe values calculated from different solvent shift equations differ appreciably but they all give the same relative order for the moments and can be used for qualitative comparison of µe for a series of closely related compounds. MIM and PPP calculations, in contrast to the experimental findings, give comparable values of µe with the same order of magnitude for all the compounds. They also show that generally µe(calc) is much greater than µe(exp). Results suggest that the excited state dipole moments of the title compounds can be evaluated for qualitative purposes by means of a simplified equation through the measurement of the frequency shift obtained from the gas-phase and solution (apolar solvent) spectra.