Assembling model tris(bipyridine)ruthenium(II) photosensitizers into ordered monolayers in the presence of the polyoxometallate anion [Co-4(H2O)(2)(alpha-PW9O34)(2)](10-)

作者：Murray Niamh S; Rudd Jennifer A; Chamayou Anne Christine; Constable Edwin C^*; Housecroft Catherine E; Neuburger Markus; Zampese Jennifer A

来源：RSC Advances, 2014, 4(23): 11766-11775.

DOI：10.1039/c4ra00085d

The complexes cis-[Ru(1)(2)Cl-2] and [Ru(1)(2)(bpy)][PF6](2) in which 1 is dioctadecyl (2,2'-bipyridine)-4,4'-dicarboxylate have been synthesized and fully characterized; the single crystal structures of the syn, syn-and anti, anti-conformers of 1 have been determined. Pressure-area isotherms for monolayers of cis-[Ru(1)(2)Cl-2] on water, aqueous Co4POM (Co4POM = K-10[Co-4(H2O)(2)(alpha-PW9O34)(2)]) or aqueous KCl subphases exhibit collapse pressures of 25-27 mN m(-1) and mean molecular areas of 220 +/- 10 angstrom(2). The similarities between these isotherms confirm that there are no significant interactions between neutral cis-[Ru(1)(2)Cl-2] and the anionic Co4POM cluster as the monolayer is formed. In contrast, use of the cationic [Ru(1)(2)(bpy)](2+) complex results in higher collapse pressures on pure water (54 mN m(-1)) or aqueous KPF6 (48 mN m(-1)) subphases, but a collapse pressure of only 17 mN m(-1) on an aqueous Co4POM subphase. The data are consistent with the monolayer forming at the air-Co4POM interface being significantly less stable than that at the air-water interface, and point to substantial electrostatic interactions between [Ru(1)(2)(bpy)](2+) and the anionic Co4POM which can lead to a reduction in the integrity of the film. The introduction of DODA (DODA = dimethyldioctyldecylammonium bromide) stabilizes the monolayers on aqueous Co4POM; mole ratios of [Ru(1)(2)(bpy)][PF6](2)-DODA of 1 : 5 and 1 : 20 lead to collapse pressures of 41 and 53 nM m(-1), respectively. Brewster angle microscopy has been used to image the monolayers and to monitor the effects of the presence of DODA. Langmuir-Blodgett (LB) films of cis-[Ru(1)(2)Cl-2] and [Ru(1)(2)(bpy)][PF6](2) with and without Co4POM have been produced on mica substrates. Atomic force microscopy reveals that LB films formed in a single dipping cycle of cis-[Ru(1)(2)Cl-2] from a water subphase are distinct from those formed on aqueous Co4POM. The former consists of islands of height approximate to 3, 6 or 9 nm; these values compare with a modelled molecular diameter of cis-[Ru(1)(2)Cl-2] of approximate to 3 nm and are consistent with the formation of mono-, bi-, or trilayers of cis-[Ru(1)(2)Cl-2]. In contrast, LB films formed from cis-[Ru(1)(2)Cl-2] on aqueous Co4POM consist of small aggregates of variable height. LB films formed from [Ru(1)(2)(bpy)][PF6](2) on aqueous subphase exhibit small aggregates but there is a very low surface coverage of the complex on mica (2 domains per mu m(2)); the coverage increases (18 domains per mu m(2)) when the films are formed in the presence of Co4POM but is significantly lower than for cis-[Ru(1)(2)Cl-2] (75 domains per mu m(2)). No significant difference in the morphology of the LB films containing [Ru(1)(2)(bpy)][PF6](2) is observed in the presence of DODA.

• 出版日期2014