Spectroscopy of Naphthalene in Simple Molecular Liquids.

Optical spectra of the first excited singlet state singlet b1u of naphthalene in cyrogenic molecular hydrocarbon alkane and alkene liquids CH4, C2H4, C2H6, C3H6, C3H8, 1-C4-H8 have been obtained and are discussed in terms of solute solvent intermolecular interaction. Data include gas to liquid shifts, Franck-Condon shifts, line widths for absorption and emission, and their temperature depencence. Naphthalene line widths and their temperature dependences and Franck-Condon shifts are smaller than those found by benzene but the gas to liquid shifts for both systems are quite similar. Based on these results and the comparison with similar benzene data, the ground and excited state Lennard-Jones type potential curves for naphthalenesolvent interactions can be generated. The main conclusions ar ethat naphthalene has a stronger interaction with the solvent than does benzene, the interaction scales with solvent polarizability, and the change in cavity radius upon excitation is greater for benzene for the naphthalene. Lifetime data have also been obtained for the naphthalene fluorescence. At low temperature, the liquid state lifetime for fluorescence is roughly the same as that found in the low pressure gas approx 300 ns. A small temeprature dependence is characterized for these low concentration solutions leading to an activation energy for naphthalene collision induced intersystem crossing of approx 100 per cm. The excimer formation and monomer regeneration mechanism reported for benzene is also observed in naphthalene C3H6 and C3H8 solutions but it is of much less importance to the overall kinetics. Author