Triplet State of α-Naphthylethylene Derivatives. Structural Effects on the Equilibrium between Planar and Perpendicular Triplet Conformations

Article abstract of DOI:10.1021/j150645a006

The properties of the triplet state of a series of 1-(α-naphthyl)ethylene derivatives have been studied by laser flash photolysis.The geometry of the triplet state has been determined from the T-T absorption spectra, the lifetime values, and the quenching rate constants by oxygen, stilbene, and ferrocene.The triplet state can be either planar (nontwisted double bond), when the ethylenic moiety is inserted into a small ring, or perpendicular (double bond twisted by 90 deg), when the planar geometry is disfavored by a strong steric hinderance.However, in most cases, there is a fast equilibrium between the planar and perpendicular triplets.These two geometries are very close in energy and therefore the equilibrium can be greatly modified by small changes in the molecular structure such as an alkyl substitution.By comparison of the triplet state of 1-(α-naphthyl)-1-phenylethylene with that of other 1-aryl-1-phenylethylenes, an experimental correlation is found between the percentage of planar triplet and the triplet energy of the aryl group.