Clean Singlet Oxygen Production by a ReI Complex Embedded in a Flexible Self-Standing Polymeric Silsesquioxane Film

Abstract

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 ReI tricarbonyldiimine complex, [(phen)Re(CO)3Br] (phen: 1,10-phenanthroline), which was found to be an efficient singlet oxygen [O2(1Δg)] photosensitizer in homogeneous solution [ΦO2(1Δg) = 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(1Δg) when illuminated with blue light (∼405 nm). The O2(1Δg) sensitization by films in acetonitrile was followed by the photooxidation of the well-known O2(1Δg) chemical trap 9,10-dimethylanthracene (DMA) and confirmed by the direct observation of the O2(1Δg) 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.