A study of excited-state dipole moments by monitoring the band width of the charge-transfer transition of ion pairs or dipolar molecules

A suitable analysis of the band-width parameters of the charge-transfer (CT) transition of ion pairs or dipolar molecules has been presented that provides information regarding the change in the ground-state dipole moment on excitation (Delta mu) or the extent of charge transfer (Delta e) for a dipolar molecule. The method has been demonstrated by determining Delta mu or Delta e for N-ethyl-4-cyanopyridinium iodide and betaine-26 [2,6-di-tert-butyl-4-(2,4,6-triphenyl-1-pyridinio)phenolate]. The relative advantage of the method for these molecules over the solvatochromic procedure has also been discussed.