The electronic spectroscopy of 2,2 '-binaphthyl in solution, cryogenic matrix and supersonic jet

The electronic spectroscopy of 2,2'-binaphthyl near 330 nm has been investi gated by absorption spectroscopy in room-temperature solution and Shpolskii matrix at 4 K and by fluorescence excitation spectroscopy in a supersonic free-jet expansion. In the solution and gas phase, where the molecules are free to form the minimum-energy conformation, the spectra are quite differe nt from those of 1,1'-binaphthyl and the parent naphthalene. However, when frozen in a matrix, aspects of the electronic spectrum resembled features o f the spectra of these molecules. The fluorescence excitation spectrum in t he free jet showed several long progressions in the torsional vibration wit h a characteristic, but anharmonic, frequency of about 30 cm(-1). The spect rum was assigned as the 1(1)B <-- 1(1)A transition with an origin transitio n, which, although it could not be observed, was estimated to be at 30 060 +/- 30 cm(-1). The frequency of 29 members of this progression allowed an a ccurate torsional potential to be calculated, which was flattened at low en ergy and approached harmonic at higher energy. The change in equilibrium to rsional angle was estimated to be 32 degrees upon electronic excitation, wi th the excited state being planar (either cis or trans). Several low-freque ncy vibrations were assigned in the gas phase that probably involve motions of the naphthalene structures as a whale about the central C-C bend. In th e matrix, the torsional vibrations were frozen out, which allowed for the o bservation and tentative assignment of several higher-frequency vibrations resembling those of the bare naphthalene. The origin frequency was measured at 28 460 cm(-1). The difference between the gas-phase and solid-phase fre quencies was attributed to the constrained structure of the molecule in the matrix.