VIBRATIONAL STRUCTURE OF THE S-0-]S-2 ABSORPTION-BAND OF CORONENE IN POLYMETHYLMETHACRYLATE, STUDIED BY TRANSIENT SPECTRAL HOLE-BURNING

The S0-->S2 absorption band of the aromatic hydrocarbon coronene in polymethylmethacrylate (PMMA) was investigated with the method of transient spectral hole-burning (TSHB), which uses the availability of a long-lived metastable triplet state. The same vibronic transitions are observed as in the site-selective fluorescence excitation spectrum of coronene in a heptane Shpol'skii matrix. The lowest e2g mode not only gives rise to the lowest false origin but also can form progressions in combination with false origins. The degree of polarization of transient zero-phonon holes is close to the theoretical value of 1/7 thal is expected for in-plane polarized transitions of a molecule with the symmetry D6h. From the homogeneous widths of resonant transient holes lifetimes less than or similar to 2 ps are obtained for the S2 vibronic states. With optically thin samples, the lineshape of resonant zero-phonon holes remains Lorentzian in the steady state of TSHB despite nonnegligible ground-state depletion. The correlation of nonresonant holes is approximately Lorentzian.