Tris(bipyridyl)ruthenium(II) surfactant complexes. The dependence of luminescence activity on monolayer deposition conditions

Abstract

Diester surfactant derivatives of tris(bipyridyl)ruthenium(II) complexes have been prepared and monolayers of these compounds spread on various subphases. The monolayers have been characterised by surface-pressure–area isotherms and transferred to glass or various fatty-acid substrates. The luminescence properties of the Ru(bpy)²⁺₃ sensitizer have been found to be extremely sensitive to the nature of the substrate, the behaviour of which is in turn influenced by the experimental conditions used for the deposition process. The variation of emission intensity (E_m) and wavelength (λ_max) with substrate thickness, film surface pressure and subphase pH and ionic strength are reported. The E_m and λ_max values are also shown to be dependent on the position and orientation of the sensitizer in the monolayer assembly.

Hydrogen gas has been detected following irradiation with u.v.–visible light of some of these monolayer assemblies immersed in water. Turnover numbers (H/Ru) of the order of 3 or 4 have been attained. Some correlation between luminescence activity and dihydrogen formation is demonstrated. The factors that maximise the emission intensity appear to account for the observed formation of dihydrogen in some of these systems.