Preparation and Properties of Surfactant Complexes of Ruthenium(II)

Abstract

New surfactant complexes RuM₂L²⁺ have been prepared where M is 2,2'-bipyridyl or o-phenanthro- line and L is one of the 4-alkyl-4'-methyl-2,2'-bipyridyls (8a)-(8e), or one of the 4,4'-dialkyl-2,2'- bipyridyls (9a)-(9e), or 1,1'-(2,2'-bipyridyl-4,4'-diyl)bis(nonadecan-1-one). This diketone was pre- pared from 2,2'-bipyridyl-4,4'-dicarboxylic acid and dioctadecylcadmium; the dialkylbipyridyls were obtained by condensing 4,4'-dimethyl-2,2'-bipyridyl with 5-alkylthiopen-2-carbaldehydes, followed by desulfurization with W5 Raney nickel. Several properties of the new complexes have been compared with those of bis(2,Y-bipyridyl)(dioctadecyl 2,2'-bipyridyl-4,4'-dicarboxy1ate)ruthenium dication (2).

Monolayers have been prepared and characterized by surface-pressure area curves; film com- pressibilities and stabilities are related to the lengths of the alkyl chains and to subphase composition. Absorption and emission spectra have been examined. The quantum yields and lifetimes of emission are similar in alcohol and water; with monolayer assemblies they are dependent on subphase com- position, and in the solid state they vary between 0.03-0.18 for Φ and 0.5-1.5 μs for τ, according to the chain lengths, which appear to affect crystal packing.

Oxygen quenched the luminescence of solutions and supported monolayers reversibly; Stern- Volmer constants and bimolecular quenching constants are given for: diester complex (2), diketone complex (6), dialkylbipyridyl complexes (5). Except with (2) the original luminescence intensity was restored by drying.

Hydrogen was not detected following irradiation with visible light of supported monolayers of pure complexes immersed in water.