Naphthalene Included within All-Silica Zeolites: Influence of the Host on the Naphthalene Photophysics

The photophysical properties of naphthalene within pure silica zeolites were studied by means of diffuse reflectance, steady state and time resolved emission 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 of the 0-0 transition, the shortening of the fluorescence lifetimes, the observation of vibronic couplings, the appearance of room temperature phosphorescence, and the shift to lower vibration energy of the Raman peaks due to the weakening of the naphthalene bonds. The electronic structure of naphthalene within different zeolites has been computed on periodic models by using both the Hartree−Fock and the Kohn−Sham theories and the theoretical 0-0 transitions evaluated from the valence and conduction bands. The theoretical results are in agreement with the experimental observation of a red shift of the 0-0 bands indicating that the naphthalene π electrons are affected by confinement effect.