title: Stabilization of ruthenium(II) polypyridyl chromophores on nanoparticle metal-oxide electrodes in water by hydrophobic PMMA overlayers.
abstract: We describe a poly(methyl methacrylate) (PMMA) dip-coating procedure, which results in surface stabilization of phosphonate and carboxylate derivatives of Ru(II)-polypyridyl complexes surface-bound to mesoporous nanoparticle TiO2 and nanoITO films in aqueous solutions. As shown by contact angle and transmission electron microscopy (TEM) measurements, PMMA oligomers conformally coat the metal-oxide nanoparticles changing the mesoporous films from hydrophilic to hydrophobic. The thickness of the PMMA overlayer on TiO2-Ru(II) can be controlled by changing the wt % of PMMA in the dipcoating solution. There are insignificant perturbations in electrochemical or spectral properties at thicknesses of up to 2.1 nm with the Ru(III/II) couple remaining electrochemically reversible and E1/2 values and current densities nearly unaffected. Surface binding by PMMA overlayers results in stable surface binding even at pH 12 with up to a ∼100-fold enhancement in photostability. As shown by transient absorption measurements, the MLCT excited state(s) of phosphonate derivatized [Ru(bpy)2((4,4'-(OH)2PO)2bpy)](2+) undergo efficient injection and back electron transfer with pH independent kinetics characteristic of the local pH in the initial loading solution.
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill , CB 3290, Chapel Hill, North Carolina 27599, United States.
authors.forename: Kyung-Ryang
authors.initials: KR
authors.lastname: Wee
authors.forename: M Kyle
authors.initials: MK
authors.lastname: Brennaman
authors.forename: Leila
authors.initials: L
authors.lastname: Alibabaei
authors.forename: Byron H
authors.initials: BH
authors.lastname: Farnum
authors.forename: Benjamin
authors.initials: B
authors.lastname: Sherman
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Lapides
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Meyer