Studies on man-made photoreaction centers and electron relay systems. 1. Enhancement of charge separation by the aid of aligned viologen units in combination with ruthenium complexes

Abstract

Tris(2,2'-bipyridine)ruthenium(II) complexes, Ru(bpy)32+, were covalently linked to viologen units to afford a model of man-made photoreaction centers. The emission from the ruthenium complex in the photoreaction centers was almost completely quenched by the linked viologen units. The relative quantum yields ( " ) of the photoinduced reduction of viologen units in the presence of the electron donor EDTA were 1-2% of those for the free Ru(bpy)32+-methyl viologen system in aqueous solutions. The ß values, however, remarkably increased in the combined system which consisted of the photoreaction center and the electron relay systems of aligned viologen units (micelle, polymer, and polysoap). The effect was attributed to the enhancement of charge separation of the photoproduced primary ion pair due to electron injection from the photoreaction centers into the electron relay system and the succeeding electron migration.

Photogeneration of Hydrogen from Polymeric Viologen Systems

“…A similar percentage was obtained in the flash experiments and both results are comparable to the results in Ref. 22. As is clear from the previous sections, and since in these experiments V+ formation is in competition with the natural decay of Rutbpyj;', 50% reduction in the yield for PVBY>+ vs. MY>+ is expected due to the decrease in the quenching rate for the same initial concentration of viologen units.…”

On the Effect of Electron Relay Redox Potential on Electron Transfer Reactions in a Water Photoreduction Model System

“…We have noticed the same trend for the same compounds (11, 12, 13) as for other bridged sub-groups of 2,2'-bipyridinium salts (14,15,16) and 1,10-phenanthroline salts (22,23,24). For n > 4, we expect that the spectra and E'/2 of each sub-group approach those of the corresponding non-bridged compounds (10,21).…”

Polymeric Design for Electron Transfer in Photoinduced Hydrogen Generation through a Coil–Globule Transition

“…[12][13][14][15][16] Meanwhile,t or ealize as ustainable society without any dependence on oil, achieving visible-light-induced water splitting,t hat is,H 2 generation is one of the most urgent tasks.T ou tilize H 2 as an alternative and renewable energy source,a rtificial photosynthetic systems,s uch as ac ombination of Ru(bpy) 3 2+/3+ /viologen 2+/+ /Pt ( Figure 1A), have been extensively researched. [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] Besides,c atalytic nanoparticles with nanometer-scale arrangement using Pt or Au [41][42][43] have been developed, considering that electronic transfer becomes remarkably effective in distances less than 2nm. [25] Furthermore,s upramolecules as photosensitizers or electronic mediators have been widely designed, for example,d endrimers and polymeric micelles.…”

“…[25] Furthermore,s upramolecules as photosensitizers or electronic mediators have been widely designed, for example,d endrimers and polymeric micelles. [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] Besides,c atalytic nanoparticles with nanometer-scale arrangement using Pt or Au [41][42][43] have been developed, considering that electronic transfer becomes remarkably effective in distances less than 2nm. [44] To promote efficient photoinduced H 2 generation, not only close arrangements of molecular arrays,but also directional controllability of electrons in catalytic nanoparticles should be explored.…”