THE ABSORPTION SPECTRUM OF DIPHENYLENE IN THE NEAR-ULTRAVIOLET

Abstract

The absorption spectrum of diphenylene has been measured in the vapor at a variety of temperatures, in solution at room temperature, and in an EPA rigid glass at 90 °K. From a consideration of the band structure and intensity distribution it was concluded that the weak absorption at 25,041 cm−1 (vapor; ƒ ≈ 10−3) is due to a symmetry-forbidden electronic transition. The theoretical prediction that the excited level is of species B1g was supported by the presence of a strong infrared band at 732 cm−1 corresponding to observed perturbing vibration of frequency 792 cm−1. The solution spectrum was found to exhibit a vibrational structure typical of a g–g forbidden excitation.