Spectra of azulene dimers.

Spectra of stable dimers of azulene in an isopentane-methylcyclohexane glass at 77 K are reported. In the 700 nm region the dimer spectrum shows a marked hyperchromism and blue shift of 100 cm-1 compared to the monomer. Assumption of a stacked 'head-to-tail' configuration for the dimer and use of the dipole-dipole approximation enables the spectral shift to be accounted for. In the U.V. region, a large loss of intensity is observed for the S2 ← So and S3 + So transitions and a number of new dimer bands are observed. The intensity redistribution is assigned to configuration mixing of the monomer states in the dimer. No luminescence could be observed from the dimer.