Ultraviolet absorption and fluorescence studies of 1-methyl-2(1H)-pyridinimine and derivative in polar and non-polar solvents

The ultraviolet (u.v.) and fluorescence spectra and relative fluorescence i ntensities of 1-methyl-2(1H)-pyridinimine (1-MIP) and 1,2-dimethylpyridinim ine (2-MIP) were measured in several solvents at room temperature. The solv ents' effect on the absorption and fluorescence spectra of MIP indicates th at the pi pi* transition shifts to higher energies (shorter wavelengths) ar e due to solvents' interactions and the formation of the pyridinium cation. One major difference in the u.v. and fluorescence spectra is the small rel ative intensity in non-polar solvents. This was attributed to the proximity effect of pi pi* and n pi* states which can lead to vibronic interactions, and to distortions of the excited-state potential surfaces. In polar solve nts, however, these two states are shifted in energy due to solvent-solute interactions, which decrease the energy of the potential surface.