Conformational Geometries and Conformation-Dependent Photophysics of Jet-Cooled 1,3-Diphenylpropane

Rotationally resolved laser-induced fluorescence excitation spectra of the S1 ← S0 transitions have been recorded for various conformers of 1,3-diphenylpropane (DPP) in supersonic free expansion. Ab initio simulation of the rotational band contours, based on the S0 rotational constants from 6-31G(d) MP2 and transition moments from 6-31G(d) CI singles calculations, provides definitive assignments of the four major spectral features to particular torsional isomers. These assignments provide rational explanations for the conformation-dependent excimer formation in jet-cooled DPP.