Photomodification of heteroleptic titanium-based, complex metal alkoxides

A heteroleptic titanium metal alkoxide (OPy)2Ti(4MP)2, where OPy = NC5H4(CH2O)-2 and 4MP = OC6H4(SH)-4, was investigated as a candidate precursor for the solution-based (sol-gel) synthesis of titanium oxide via the photoactivation of intermolecular linking reactions (e.g., hydrolysis/condensation). The evolution of the electronic structure of the solution-based molecule arising from conventional (dark) chemical reaction kinetics was compared with that of samples exposed to ultraviolet (UV) radiation at wavelengths of λ = 337.1 nm and 405 nm using UV-visible absorption spectroscopy. Photoinduced changes in the spectra were examined as a function of both the incident wavelength of exposure and the total fluence. Experimental results confirm the UV-induced modification of spectral absorption features, attributed to ligand-localized and charge transfer transitions accompanied by structural changes associated with hydrolysis and condensation. The photoenhancement of reaction kinetics in these processes was confirmed by the increased modification of the absorption features in the solution spectra, which saturated more rapidly under UV-illumination than under dark conditions. Similar saturation behaviors were observed for both the 337.1 nm and the 405 nm incident wavelengths with the same total deposited energy density indicating a relative insensitivity of the photoinduced response to excitation energy for the wavelengths and fluences studied.