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The excited state lifetimes of oxazine dyes nile blue and oxazine 720 show a significant solvent dependence. As an aid to the interpretation of the decay in acidic environments the ground electronic states and the first singlet excited states of oxazine monocations and dications have been studied by methods of quantum chemistry. Ab initio calculations carried out on the lower members on this series show a significant increase of the electron densities of the ring nitrogen on excitation. The calculated electron energies also suggest that the second proton attaches to the ring nitrogen in the excited states, in contrast to the ground states where (in the case of oxazine 720) the second proton attaches to the terminal nitrogen.

The assignment of the vibrational spectra of phenol has been reexamined on the basis of Raman and new IR measurements and theoretical analysis of the normal modes of vibrations in the electronic ground state. The infrared spectra of C6H5OH, C6D5OD, and C6D5OH have been studied in solution and vapor phases, as well as has the Raman spectra in solutions. New experimental data were obtained from infrared linear dichroism (IR-LD) studies of phenol aligned in uniaxially oriented nematic liquid crystal solution. The measured dichroic ratios and orientation factors indicate an effective Cs symmetry of the molecule with coplanar orientation of OH bond with the benzene ring and supply unique information on the extent of symmetry lowering of benzene normal modes. The fundamental vibrational frequencies, force constants, and dipole derivatives have been calculated by ab initio quantum chemical methods applying the B3P86 density functional approximation with 6-311G** basis set. The force field optimized by means of a least-squares scaling procedure for phenol-d0 (using six scale factors) was used to calculate the frequencies (with a mean deviation from the observed values less than 1%), normal modes, potential energy distributions, transition moment vectors, and IR intensities for phenol-d0, -d1, -d5, and -d6 isotopomers. Compared to the deviations between the calculated and observed absorption intensities, a more satisfactory correlation was found between the calculated and experimentally determined vibrational transition moment directions. The results indicate unanimously that the perturbation of the normal modes of benzene by the asymmetric hydroxyl substituent is so great that the previous practice of assigning the normal vibrations of phenol to those of benzene or even to C2v symmetry species is not justified.

The infrared and far infrared spectra of complexes formed between p-benzoquinone and phenol derivatives were studied in the crystalline state. The spectra showed the compounds to be weakly polar charge transfer complexes with hydrogen bonds. In the far infrared region hydrogen bond vibrations and internal vibrations forbidden in the free molecules were observed.

A picosecond laser system consisting of two tuneable dye lasers pumped synchronously by a mode locked argon-ion laser has been used for studying the relaxation of the S1excited states of dye molecules Nile Blue and Oxazine 720. The dependence of the excited state lifetimes on the solvent and on the temperature are discussed. Both intramolecular and intermolecular decay channels contribute to the radiationaless de-excitation. The mechanism of intramolecular decay is different, while that of intermolecular decay is very similar for the two molecules.