Interfacial Energy Conversion in RuII Polypyridyl-Derivatized Oligoproline Assemblies on TiO2

Abstract

Solid-phase peptide synthesis has been applied to the preparation of phosphonate-derivatized oligoproline assemblies containing two different Ru(II) polypyridyl chromophores coupled via "click" chemistry. In water or methanol the assembly adopts the polyproline II (PPII) helical structure, which brings the chromophores into close contact. Excitation of the assembly on ZrO2 at the outer Ru(II) in 0.1 M HClO4 at 25 °C is followed by rapid, efficient intra-assembly energy transfer to the inner Ru(II) (k(EnT) = 3.0 × 10(7) s(-1), implying 96% relative efficiency). The comparable energy transfer rate constants in solution and on nanocrystalline ZrO2 suggest that the PPII structure is retained when bound to ZrO2. On nanocrystalline films of TiO2, excitation at the inner Ru(II) is followed by rapid, efficient injection into TiO2. Excitation of the outer Ru(II) is followed by rapid intra-assembly energy transfer and then by electron injection. The oligoproline/click chemistry approach holds great promise for the preparation of interfacial assemblies for energy conversion based on a family of assemblies having controlled compositions and distances between key functional groups.