Excited-State Properties of the Four Stereoisomers of 1-(9-Anthryl)-4-phenyl-1,3-butadiene: Evidence of Adiabatic and Diabatic Deactivation Pathways

The photophysics and photochemistry of the four geometrical isomers of 1-(9-anthryl)-4-phenyl-1,3-butadiene have been extensively studied by stationary and pulsed spectrometry in nonpolar solvent. Fluorimetric and laser flash techniques were used to measure the quantum yields and lifetimes of the lowest excited states of singlet and triplet multiplicity at different temperatures. This paper reports the spectral characterization of the four isomers and their derived parameters of the radiative, nonradiative, and reactive relaxation pathways. The isomerization proceeds through triplet diabatic and/or adiabatic mechanisms, generally with low quantum yield, owing to high torsional barriers in the S 1 state and small T 1 population quantum yields, due to the very fast S 1 → S 0 internal conversion. At high temperature, a singlet diabatic mechanism is also operative.