The Electronic Absorption Spectra of Tropolone and Its Dimer

Abstract

The electronic absorption spectra of tropolone either in a mixed solvent of methylcyclohexaneisopentane (1: 1) or a polyethylene film were measured at room temperature and 77 K. The spectral data as well as the results of MO calculations demonstrated the formation of a tropolone dimer in the 'mixed solvent at low temperatures, which possesses a cyclic structure due to hydrogen bonding. The polarized absorption spectrum of tropolone monomer was measured in the stretched polyethylene film at 101 K, and the origins of the two differently polarized electronic transitions in the wavelength region of 210--260 nm have been clarified, being at 249.7 nm and at 244.7 nm. The spectral changes on the dimer formation observed for the lowest two electronic bands at 373.4 nm and 321.3 nm of the monomer are explained in terms of an exciton splitting model.