RIGID GROUND-STATE STRUCTURE OF 1,2-DIHYDRO-3H-BENZ[E]INDEN-3-ONE DEFORMED IN THE LOWEST ELECTRONIC TRIPLET-STATE

The X-ray diffraction of crystalline 1,2-dihydro-3H-benz[e]inden-3-one (DHBI) reveals that the molecular geometry is fully planar in the ele ctronic ground state. Glassy solutions of naphthaldehyde, 2-acetonapht hone and methyl 2-naphthoate in the mixtures methylcyclohexane/iso-pen tane (MIP) and methanol/ethanol (ME) are phosphorescent. DHBI in ME sh ows phosphorescence, but in MIP it is non-phosphorescent. The phosphor escence spectra of these compounds and of naphthalene have a strong re semblance. This is in accordance with a molecular distortion in the lo west triplet state, which decouples the a electron systems of the carb onyl group and the naphthyl group. The absence of phosphorescence of D HBI in MIP, indicates a geometry of the triplet state, having a non-pl anar naphthalene ring, when the molecule is in the non-hydrogen bonded form.