Interfacial self-assembly, characterization, electrochemical, and photo-catalytic properties of porphyrin-ruthenium complex/polyoxomelate triad hybrid multilayers

Abstract

Triad hybrid multilayers composed of tetrapyridylporphyrin (TPyP), bis(2,2′-bipyridyl)ruthenium chloride [Ru(bpy)2Cl2], and phosphomolybdic acid (PMA) have been prepared at the gas-liquid interface. The tetraruthenated porphyrin of TPyP-Rubpy complex was synthesized by the coordination interaction of TPyP with Ru(bpy)2Cl2. Surface pressure–area isotherms indicated that the average molecular area of the TPyP-Rubpy complex was in the range of 3.1–3.3nm2 when the PMA concentration was 0.1–0.3mg/mL in the subphases. Monolayers of the TPyP-Rubpy/PMA triad hybrids were transferred onto the substrate surfaces by using the Langmuir-Blodgett (LB) method. The absorption spectra of the hybrid LB films revealed several strong peaks between 300 and 440nm, attributed to the π–π* electron transfer of the Rubpy substituent and the Soret band of TPyP. Under radiation, the TPyP-Rubpy complex gave off strong luminescence in the wavelength between 600 and 700nm, attributed to the emissions from the Rubpy and TPyP substituents. These emissions largely weakened in the LB films of TPyP-Rubpy/PMA triad hybrids. Cyclic voltammograms showed six couples of redox waves in the potential range from −1.2 to 0.6V (vs Hg/HgCl2), which could be designated for the electron transfer processes of TPyP, Rubpy and PMA, respectively. Finally, it was revealed that the present triad hybrid LB films can be used as efficient light-harvesting units for the photo-catalytic oxidation of organic dyes and for light-induced photocurrent generation.