Vibrational structure of the S 0→S 2 absorption band of coronene in polymethylmethacrylate, studied by transient spectral hole-burning

Abstract

The S 0→S 2 absorption band of the aromatic hydrocarbon coronene in polymethylacrylate (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 e 2g mode not only gives rise to the lowest false origin but also can form progression in combination with false origins. The degree of polarization of transient zero-phonon holes is close to the theoretical value of 1 7 that is expected for inplane polarized transitions of a molecule with the symmetry D 6h. From the homogeneous widths of resonant transient holes lifetimes ≲ 2 ps are obtained for the S 2 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.