Satellite hole investigations of the hole-burning mechanism and vibrational mode coupling of 9-aminoacridine doped in glycerol-water glasses at different pH values

The vibrational modes of the excited electronic state of 9-aminoacridine (9-AA) doped in amorphous glasses of glycerol and water mixtures have been examined via the satellite holes in the persistent hole-burned spectra. The satellite holes with high resolution were used to characterize tautomer structures of 9-AA at different pH values and provide information on the vibrational mode coupling for the study of guest-host interactions. More fundamental modes were observed for monoprotonated 9-AA, but stronger couplings among the 390, 1162, and 1338 cm^-1 modes are reflected in the combination modes for neutral 9-AA. Normal mode calculations of vibrational frequencies were performed to help mode assignments. Deuteriation of the amino group protons is carried out to distinguish between the vibrational modes of the acridine ring and the amino group. Franck-Condon factors were obtained from hole-burned spectra to assist in understanding the intensity distributions of the burned holes. Proton transfer between the chromophore and matrix, triggered by charge density migration along the short axis of 9-AA via electronic excitation, is proposed for the hole-burning mechanism.