Site-selection spectroscopy and hole-burning of ionic dyes in amorphous hosts at low temperature

Abstract

The hole-burning (HB) mechanism of the ionic dyes resorufin and cresyl violet was investigated in various glasses and polymers at liquid helium temperature. By means of hole-filling experiments the spectral distance of the photoproduct absorption maximum to that of the original molecule δ max was determined. It was observed that δ max and the electron-phonon coupling strength, S, increase with host polarity, Z, in the ionic dyes studied, whereas δ max and S are both independent of Z in the neutral free-base porphin molecule. A linear relation between δ max and S was found for all cases. The results suggest that these ionic dye systems undergo intermolecular photochemical hole-burning with high HB efficiency. Furthermore, two differently solvated species of resorufin in alcoholic glasses (ethanol and glycerol) were identified, and the vibrational frequencies of ground and first excited singlet states were obtained for both species. It is inferred that one of the species is hydrogen bonded to the host, whereas the other is a “free” resorufin molecule. Although hydrogen-bonding solvents enhance the HB efficiency, they are not necessary for the hole-burning process to occur.