ELECTRONIC ABSORPTION-SPECTRA AND THERMAL-STABILITY OF CIS-TRANS ISOMERS OF DIPHENYLBUTADIENE CATION RADICALS

The cation radicals of the three cis-trans isomers of 1,4-diphenylbutadiene have been generated by γ-irradiation in a matrix at 77 K and in acetonitrile solution at room temperature by secondary electron transfer. The cation radicals exhibit two strong absorption bands, the more intense between 530 and 560 nm and another between 800 and 850 nm. The absorption bands of the cis,trans and the cis,cis isomers are red-shifted and have reduced oscillator strengths relative to those of the trans,trans isomer. In acetonitrile, cations with distinct absorption spectra were formed that do not thermally interconvert on a nanosecond time scale. Slow isomerization at room temperature does occur with an estimated lifetime of ≈ 25 μs. © 1990.