Electronic Spectroscopy of the Titanium Centers in Titanium Silicalite

Studies of the electronic structure of titanium centers in titanium silicalite (TS-1) catalytic materials were carried out using electronic absorption and emission spectroscopy. A long-lived phosphorescent excited state with an emission maximum at 490 nm in the near UV was unambiguously assigned to the titanium. Resolved in the emission envelope was vibronic structure in 965 cm -1 mode, which corresponds to the Si−O−Ti stretching mode in TS-1. The lowest energy excited state is significantly lower in energy than was previously suggested by diffuse reflectance absorption spectroscopy. Emission excitation spectra indicate that, contrary to previous assertions, there are electronic transitions throughout the spectral region from ∼23000 to 48000 cm -1 . These observations bring into question long-standing structural arguments for the coordination of titanium in the silicalite lattice that have been made using electronic spectroscopy.