title: Formation of assemblies comprising Ru-polypyridine complexes and CdSe nanocrystals studied by ATR-FTIR spectroscopy and DFT modeling.
abstract: The interaction between CdSe nanocrystals (NCs) passivated with trioctylphosphine oxide (TOPO) ligands and a series of Ru-polypyridine complexes-[Ru(bpy)(3)](PF(6))(2) (1), [Ru(bpy)(2)(mcb)](PF(6))(2) (2), [Ru(bpy)(mcb)(2)](BarF)(2) (3), and [Ru(tpby)(2)(dcb)](PF(6))(2) (4) (where bpy = 2,2'-bipyridine, mcb = 4-carboxy-4'-methyl-2,2'-bipyridine, tbpy = 4,4'-di-tert-butyl-2,2'-bipyridine; dcb = 4,4'-dicarboxy-2,2'-bipyridine, and BarF = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate)-was studied by attenuated total reflectance FTIR (ATR-FTIR) and modeled using density functional theory (DFT). ATR-FTIR studies reveal that when the solid film of NCs is exposed to an acetonitrile solution of 2, 3, or 4, the complexes chemically bind to the NC surface through their carboxylic acid groups, replacing TOPO ligands. The corresponding spectral changes are observed on a time scale of minutes. In the case of 2, the FTIR spectral changes clearly show that the complex adsorption is associated with a loss of proton from the carboxylic acid group. In the case of 3 and 4, deprotonation of the anchoring group is also detected, while the second, "spectrator" carboxylic acid group remains protonated. The observed energy difference between the symmetric, ν(s), and asymmetric, ν(as), stretch of the deprotonated carboxylic acid group suggests that the complexes are bound to the NC surface via a bridging mode. The results of DFT modeling are consistent with the experiment, showing that for the deprotonated carboxylic acid group the coupling to two Cd atoms via a bridging mode is the energetically most favorable mode of attachment for all nonequivalent NC surface sites and that the attachment of the protonated carboxylic acid is thermodynamically significantly less favorable.
authors.affiliation: Physical Chemistry & Applied Spectroscopy, Los Alamos National Laboratory, MS J567, Los Alamos, New Mexico 87545, USA.
authors.forename: Alexey Y
authors.initials: AY
authors.lastname: Koposov
authors.forename: Thomas
authors.initials: T
authors.lastname: Cardolaccia
authors.forename: Victor
authors.initials: V
authors.lastname: Albert
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Badaeva
authors.forename: Svetlana
authors.initials: S
authors.lastname: Kilina
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Meyer
authors.forename: Sergei
authors.initials: S
authors.lastname: Tretiak
authors.forename: Milan
authors.initials: M
authors.lastname: Sykora
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry*; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D010316:Particle Size; D011725:Pyridines / Q000737:chemistry*; D011789:Quantum Theory; D012428:Ruthenium / Q000737:chemistry*; D018036:Selenium Compounds / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties
chemical_list: D019187:Cadmium Compounds; D009942:Organometallic Compounds; D011725:Pyridines; D018036:Selenium Compounds; D012428:Ruthenium; C058667:cadmium selenide