Fully resonant four-wave mixing spectroscopy of pentacene and dye molecules in condensed phases

Abstract

Dispersive multi-resonant coherent anti-Stokes and Stokes (CARS and CSRS) data are reported for pentacene in naphtha­ lene. The vibronic resonances are associated with the lowest excited singlet state of pentacene. Attention is focused on the 755 cm^ ground state fundamental of pentacene, its excited state counterpart at 747 cm~^ and their two partners which move with the detuning, d, of the laser away from the electronic origin transition at (d = Pentacene in naphthalene appears to be unusual in that excited electron­ ic state CARS resonances are observed for negative detunings which are large relative to the inhomogeneous linewidth of the Wq,q transition. Temperature dependent studies indicate that the excited state population mechanism involves phonon hotband absorption. Power broadening data for the 755 cm~^ resonance obtained for negative detunings are discussed in terms of a distribution of dynamic Stark shifts resulting from the site inhomogeneous line broadening of vibronic transitions. Novel temperature dependent data for positive detuning (d = 4 cm ) are presented and tentatively interpreted in terms of the interplay between dephasing induced coherent emission (DICE from the excited state population) and the temperature dependence of the phonon sideband absorption building on the (0',0) band. CARS and CSRS data are presented which are