Clean singlet oxygen production by a Re^I complex embedded in a flexible self-standing polymeric silsesquioxane film

Rhenium complexes are versatile molecular building blocks whose tunable photophysical properties are useful in diverse opto-related applications. Herein we report the synthesis and characterization of a novel Re^I tricarbonyldiimine complex, [(phen)Re(CO)₃Br] (phen: 1,10-phenanthroline), which was found to be an efficient singlet oxygen [O₂(¹Î"_g)] photosensitizer in homogeneous solution [Φ_O2(¹Î"g) = 0.55 (dichloromethane) and 0.16 (dimethylformamide)]. The photophysical properties of [(phen)Re(CO)₃Br] were thoroughly characterized in solution and modeled by means of density functional theory (DFT) and time-dependent (TD)-DFT quantum mechanical calculations. The Re complex was incorporated into a flexible polymeric silsesquioxane (SSO) film, which has excellent dopant compatibility, chemical resistance, and mechanical properties. When [(phen)Re(CO)₃Br] is embedded in the SSO film, it is found to retain most of the photophysical characteristics observed for the complex in solution. In particular, the [(phen)Re(CO)₃Br]-doped SSO films were able to photosensitize O₂(¹Î"_g) when illuminated with blue light (∼405 nm). The O₂(¹Î"_g) sensitization by films in acetonitrile was followed by the photooxidation of the well-known O₂(¹Î"_g) chemical trap 9,10-dimethylanthracene (DMA) and confirmed by the direct observation of the O₂(¹Î"_g) luminescence spectrum (centered at 1270 nm) and the measurement of its kinetic profile. These results highlight the potential application of this type of polymeric material in the production of biological- or microbial-photoinactivating flexible surfaces or in the implementation of interfacial solid/liquid strategies for the photoinduced oxidation of organic compounds in solution.