Excitation wavelength dependence of the Raman-Stokes shift of N,N-dimethyl-p-nitroaniline

Raman spectra of N,N-dimethly-p-nitroaniline have been measured in various solvents. The Raman-Stokes shift of the band assigned to the NO2 stretching mode excited at 488 nm was found to be linearly dependent on the pi-pi(*) absorption band center. Furthermore, it is found that the Raman-Stokes shift of the NO2 stretching mode is dependent upon the excitation wavelength. The extent of the shift when excited at 355 versus 488 nm is almost linearly dependent on the vibrational bandwidth of the NO2 mode. The phenomenon is interpreted as the result of the solvation state selective excitation of the vibrational mode as in the case of phenol blue [Yamaguchi , J. Chem. Phys. 109, 9075 (1998); 109, 9084 (1998)]. (c) 2006 American Institute of Physics.