ELECTRONIC DEPHASING AND ELECTRON-PHONON COUPLING OF ALUMINUM PHTHALOCYANINE TETRASULFONATE IN HYPERQUENCHED AND ANNEALED GLASSY FILMS OF ETHANOL AND METHANOL OVER A BROAD TEMPERATURE-RANGE

The electronic dephasing (spectral dynamics) and electron-phonon coupl ing of aluminum phthalocyanine tetrasulphonate (APT) in glassy films o f ethanol and methanol were investigated by nonphotochemical hole burn ing over a broad temperature range, similar to 5-100 K. Films formed b y hyperquenching (similar to 10(6) K s(-1)) at 4.7 K were studied as w ell as films that were subsequently annealed at temperatures up to sim ilar to 170 K. Results are compared against those for APT in glassy wa ter [Kim et al., J. Phys. Chem. 99, 7300 (1995); Reinot et al., J. Che m. Phys. 104, 793 (1996)]. As in the case of water, the linear couplin g is weak with a Huang-Rhys factor S similar to 0.4 but:the mean phono n frequencies for ethanol and methanol of 26 and 17 cm(-1) are conside rably lower than the 38 cm(-1) value for water. These modes are assign ed as pseudolocalized with significant amplitude (libration) localized an APT. Below about 8 K, the electronic dephasing/spectral diffusion is dominated by coupling to the tunneling intrinsic two-level systems of the glass. At higher temperatures the electronic dephasing is domin ated by the exchange coupling mechanism, which derives from diagonal q uadratic electron-phonon coupling. Here, for both ethanol and water, a pseudolocalized model(s) at similar to 50 cm(-1) is operative. This f requency corresponds to a peak in the spectral density of the liquids which for water is due to the transverse acoustic mode. The results sh ow that the modes responsible for linear and quadratic coupling are di stinctly different. Implications of this for optical coherence loss in liquids are considered. Novel results from annealing experiments are reported and discussed in terms of the complex phase diagrams of ethan ol and methanol. Formation of the glass from the supercooled liquid ju st above the melting point of a crystalline phase leads to a marked re duction (similar to 10X) in the homogeneous width of the zero-phonon h ole at 4.7 K. This is interpreted in terms of a reduction in the densi ty of intrinsic two-level systems due to reduced structural disorder o f the glass formed from the supercooled liquid. As in the case of wate r, the highly efficient hole burning in glassy ethanol and methanol is observed to become highly inefficient upon formation of a crystalline phase as predicted by the Shu-Small mechanism for nonphotochemical ho le burning. The close connection between this mechanism and Onsager's inverse snowball effect for solvent dynamics around an instantaneously created point charge or dipole in a liquid is emphasized. (C) 1997 Am erican Institute of Physics.