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.

Electronic Properties and Structure of Assemblies of CdSe Nanocrystal Quantum Dots and Ru‐Polypyridine Complexes Probed by Steady State and Time‐Resolved Photoluminescence

“…The details of the adsorption mechanism will be discussed in a separate publication. [ 36 ] Deprotonation of the carboxylic acid group in the presence of CdS NQDs was recently observed by McQuillan and co-workers using the ATR-FTIR technique. [ 12 ] To confi rm that the deprotonation of 2 is due to the presence of the NQDs, we have performed control experiments wherein the stock solution of 2 was mixed with 10 − 4 M solutions of TOPO and TOP in benzonitrile.…”

Ultrafast intersystem-crossing in platinum containing π-conjugated polymers with tunable spin-orbit coupling

“…For all simulations we used hybrid B3LYP31 functional coupled with LANL2dz* (Pt)/6-31G* (all other atoms) basis set as implemented in the Gaussian09 suite32. Such model chemistry has shown an excellent quantitative performance in similar organo-metallic compounds in a number of previous studies3334. 20 lowest singlet (triplet) states have been calculated and analyzed using the natural transition orbital (NTO) approach22 to determine their characteristic nature.…”

Ligand Induced Spectral Changes in CdSe Quantum Dots

“…In previous theoretical works the energy difference between the distinct interacting modes has been calculated to be small. 46,47 Accordingly, ligands are supposed to assume different anchoring geometries over the CPMD trajectory. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 11 Our molecular dynamics simulations confirm such a hypothesis for the QD-2 system, see During the dynamics, which cover ca.…”