Singlet Oxygen Production upon Two-Photon Excitation of TiO2 in Chloroform

Singlet oxygen (O-1(2)) signals observed upon illumination at 532 nm are a consequence of TiO2 excitation in a two-photon process, and at 355 nm in a one-photon pathway. After corrections for light reflectance, the relative quantum yields of O-1(2), production are 0.23 +/- 0.01 and 0.22 +/- 0.02 for 532 and 355 nm excitation, respectively. Total quenching rate constants of O-1(2) removal by TiO2 particles are near the diffusion-controlled rate limit. By employing O-1(2) as a probe, we have established an efficient and simple method to elucidate the nature of TiO2 photoexcitation.