Singlet oxygen formation by porous Si in solution

Singlet oxygen formation by porous Si in solution has been demonstrated. It has been shown that the absorption band of 1,3-diphenylisobenzofuran (DPBF) in benzene becomes smaller, i.e., DPBF is degraded, by irradiating green or red light if the powder of fresh porous Si is dispersed in the solution. The effect was drastically suppressed by the formation of a monolayer of backbonded oxide at the surface of nanocrystals. The degradation was accelerated when the solution was bubbled with oxygen gas. These results indicate that electronic excitation of Si nanocrystals is transferred to molecular oxygen dissolved in solution, resulting in the formation of singlet oxygen. Generated singlet oxygen reacts with DPBF, forming endoperoxides, which in turn decompose to yield irreversible products. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.