Laser-induced photopatterning of organic-inorganic TiO2-based hybrid materials with tunable interfacial electron transfer

Hybrid organic-inorganic materials based on TiO2 gels demonstrate high photosensitivity. Associated with their stable photochromic behavior, these make them suitable for laser-induced photopatterning. We show that the electronic coupling along the extended interface between the inorganic, TiO2-based gel, and the organic, poly(hydroxyethyl methacrylate) networks allows (i) a rapid scavenging of the photo-excited holes by the polymer, (ii) an efficient trapping of the photo-exited electrons as small polarons (Ti3+) that develop "dark" absorption continuum covering the spectral range from 350 nm (UV) to 2.5 mu m (IR), and (iii) long-term (over months) conservation of trapped charges at high number density. Furthermore, we give the proof that the electron transfer depends on the material microstructure, which can be affected by the material chemistry and processing. Undeniably, a delay between the gelation of the system and the organic polymerization step allows tuning the photochromic responses of the resulting nanocomposites. A comparison is made between the prepared gel-based samples and a reference sample, which is obtained by the organic copolymerization of functional precondensed inorganic building units, titanium oxo-clusters, Ti16O16(OEt)(24)(OEMA)(8) with hydroxyethyl methacrylate. The experiments show the highest values of quantum yield (12%) and Ti3+ concentration (1.7 x 10(20) cm(-3) or 14% of titanium atoms) attained in samples where the organic polymerization is induced after gelation. This behavior is explained by a strong coupling between the organic and the inorganic components of the hybrid towards the hole exchange and a poor coupling towards the electron exchange.