Conformational geometries and conformation-dependent photophysics of jet-cooled 1,3-diphenylpropane

Rotationally resolved laser-induced fluorescence excitation spectra of the S-1 <-- S-0 transitions have been recorded for various conformers of 1.3-di phenylpropane (DPP) in supersonic free expansion. Ab initio simulation of t he rotational band contours, based on the S-0 rotational constants from 6-3 1G(d) MP2 and transition moments fr-om 6-31G(d) CI singles calculations, pr ovides definitive assignments of the foul major spectral features to partic ular torsional isomers. These assignments provide rational explanations for the conformation-dependent excimer formation in jet-cooled DPP.