THEORETICAL AND JET SPECTROSCOPIC INVESTIGATIONS OF ENERGETICS AND STRUCTURES FOR THE LOW-LYING SINGLET STATES OF FLUORENE AND 9,9'-SPIROBIFLUORENE

摘要

Ab initio, semiempirical and spectroscopic studies of fluorene (FR) and 9,9'-spirobifluorene (SBF) were performed to elucidate ir-orbital interaction between two fluorenyl rings of SBF and to predict the energies of the low-lying singlet electronic slates of the molecules. Energies and symmetries of pi-orbitals of FR and SBF molecules were determined by 3-21G and 6-31G* calculations on the optimized structures, The INDO/S-CIS semiempirical method was applied to predict the excited state energies, the transition dipole moments and the oscillator strengths for the optical transitions. Laser-induced fluorescence (LIF) excitation spectra were measured for FR and SBF cooled in pulsed supersonic expansions of He in the ranges 283.7-296.7 nm and 289.1-305.6 nm, respectively. In the LIF excitation spectra of FR and SBF, highly resolved vibronic bands were observed having the band origins of 33 791 and 33 047 cm(-1), respectively. The spectral shift of the 0-0 band of SBF to red by 744 cm(-1) may be attributed to the spiroconjugation arising from the interaction of four p(pi) orbitals in the different planes. [References: 33]