Weak triplet-triplet absorption spectra of cyanobenzenes

Transient absorption spectra in the visible region have been measured for benzonitrile, o-, m- and p-dicyanobenzene, and 1,2,4,5-tetracyanobenzene in ether-isopentane-ethanol glass at 77 K by means of a flash spectroscopy technique with a sample cell of long path length. Weak transient absorptions decaying at the same rates as the corresponding phosphorescences have been detected in the visible region (400–600 nm), and are attributed to TT transitions which may be associated with local excitations within the benzene ring.