Electronic spectra of biphenylene and diazabiphenylenes

Abstract

The absorption, linear dichroism (l.d.) and magnetic circular dichroism (m.c.d.) spectra of biphenylene (1), 1,8-diazabiphenylene (2) and 2,7-diazabiphenylene (3) have been measured. The c.d. spectra of the β-cyclodextrin complexes with 1, 2 and 3 have also been measured. The first [(23.0–36.0)× 10³ cm^–1] and second [(36.0–50.0)× 10³ cm^–1] absorption bands of 1, 2 and 3 have been assigned by using the observed spectra and the results of CNDO/S CI calculations. It is concluded that the b_3u vibration with a frequency of ca. 780 cm^–1 takes part in the vibronic coupling between the first and second excited singlet states of 1 and that the second absorption band of 1 is composed of two electronic transitions polarized along the short and long axes.