An experimental and theoretical study of the photophysical properties and the dipole moments of methoxynitronaphthalenes

Isomeric methoxynitronaphthalenes (MNN, 14 possible isomers, cf. Scheme 1) were studied theoretically and experimentally. PPP calculations were carried out for all possible isomers and the results were compared with the experimental electronic absorption, fluorescence, and phosphorence spectra of selected isomers. Also the phosphorescence lifetimes were determined. Theoretical ground-state dipole moments of MNN were obtained as a combination of the pi-component (PPP method) and the sigma-component (a vector sum of sigma-bond and group moments). The experimental groundstate dipole moments were measured for a series of MNN (on a dipole meter) and compared with the theoretical values. The effect of solvent polarity upon the electronic absorption and Fluorescence spectra of selected MNN was studied and the solvatochromic method using the Bakhshiev and Kawski-Chamma-Viallet equations and the ground-state dipole moments was employed to obtain the experimental first excited singlet-state dipole moments.