Evidence for L-1(a) fluorescence from jet-cooled 3-methylindole-polar solvent complexes

The ratio of nonresonant two-photon induced fluorescence excitation spectra using circularly and linearly polarized light for jet-cooled 3-methylindol e complexed with a series of increasingly basic hydrogen bond acceptors (wa ter, methanol, ethanol, diethylether, diethylamine and triethylamine) is co nsistent with an avoided crossing of the two lowest excited singlet states, L-1(a) and L-1(b). The dispersed fluorescence of these from this series al so reflects the crossing, providing a definitive L-1(a) jet-cooled fluoresc ence spectrum. The jet-cooled L-1(a) fluorescence spectrum is not broad and redshifted, but has vibronic structure that agrees well with ab initio pre dictions and is similar to that of L-3(a) phosphorescence. (C) 2000 America n Institute of Physics. [S0021-9606(00)00837-0].