Naphthalene included within all-silica zeolites: Influence of the host on the naphthalene photophysics

The photophysical properties of naphthalene within pure silica zeolites wer e studied by means of diffuse reflectance, steady state and time resolved e mission spectroscopy, fluorescence polarization, and FT-Raman spectroscopy. The experimental results indicate that naphthalene is strongly affected by the zeolite host. This distortion is reflected in the bathochromic shift o f the 0-0 transition, the shortening of the fluorescence lifetimes, the obs ervation of vibronic couplings, the appearance of room temperature phosphor escence, and the shift to lower vibration energy of the Raman peaks due to the weakening of the naphthalene bonds. The electronic structure of naphtha lene within different zeolites has been computed on periodic models by usin g both the Hartree-Fock and the Kohn-Sham theories and the theoretical 0-0 transitions evaluated from the valence and conduction bands. The theoretica l results are in agreement with the experimental observation of a red shift of the 0-0 bands indicating that the naphthalene pi electrons are affected by confinement effect.