ELECTRONIC-SPECTRA OF MATRIX-ISOLATED TOLAN - SITE SELECTIVE ONE-PHOTON AND 2-PHOTON SPECTRA

Site-selective fluorescence and one- and two-photon fluorescence excitation spectra of low-lying electronic singlet states of tolan (diphenylacetylene) embedded in different matrices (N2, Ar, Kr) are presented and discussed. The results are compared to spectra obtained from a Shpolskii matrix and from supersonic jet investigations. Only the fluorescence spectra agree with the results from the jet study. The one- and especially the two-photon excitation spectra exhibit major differences compared to the jet results. CNDO/S-SDCI calculations suggest that the first three excited singlet states are very close together in tolan. The observed discrepancies are discussed in relation to the influence of different environments on the location of different excited states. In condensed phase the lowest excited singlet state is undoubtedly 1(1B)1u. This state is responsible for the fluorescence and the low-energy part of one- and two-photon absorption. In the gas phase it is, however, possible that 1(1A)u has a lower energy than 1(1B)1u. The onset of the 1(1B)2u band is estimated to lie between 1000 and 2000 cm-1 above 1(1B)1u in a condensed-phase environment.