Spin-selective charge recombination in complexes of CdS quantum dots and organic hole acceptors.

This paper describes the mechanisms of charge recombination on both the nanosecond and microsecond time scales in a donor-acceptor system comprising thiol-modified bis(diarylamino)4,4'-biphenyl (TPD) molecules attached to a CdS quantum dot (QD) via the thiolate linker. Transient absorption measurements, in conjunction with EPR and magnetic field effect studies, demonstrate that recombination on the nanosecond time scale is mediated by radical pair intersystem crossing (RP-ISC), as evidenced by the observation of a spin correlated radical ion pair, the formation of the localized (3)*TPD state upon charge recombination, and the sensitivity of the yield of (3)*TPD to an applied magnetic field. These experiments show that the radical spins of the donor-acceptor system have weak magnetic exchange coupling (|2J| < 10 mT) and that the electron donated to the QD is trapped in a surface state rather than delocalized within the QD lattice.

Photoisomerisation and ligand-controlled reversible aggregation of azobenzene-functionalised gold nanoparticles.

The photochemical behaviour of functionalised gold nanoparticles (AuNPs) carrying azobenzenethiolate-alkylthiolate monolayers was investigated. Repeated trans-cis and cis-trans isomerisation cycles could be performed in all cases with high efficiency. Reversible photoinduced aggregation was observed when azothiolates with long alkyl spacers (≥C7) were combined with short (C5) alkylthiolate coligands.

The chemical environments of oleate species within samples of oleate-coated PbS quantum dots.

A combination of FT-IR, (1)H NMR, nuclear Overhauser effect (NOESY), and diffusion-ordered (DOSY) NMR spectroscopies shows that samples of oleate-coated PbS quantum dots (QDs) with core radii ranging from 1.6 to 2.4 nm, and purified by washing with acetone, contain two species of oleate characterized by the stretching frequencies of their carboxylate groups, the chemical shifts of their protons, and their diffusion coefficients.

Spontaneous multielectron transfer from the surfaces of PbS quantum dots to tetracyanoquinodimethane.

This paper describes an investigation of the interfacial chemistry that enables formation of a multielectron ground-state charge-transfer (CT) complex of oleate-coated PbS quantum dots (QDs) and tetracyanoquinodimethane (TCNQ) in CHCl3 dispersions. Thermodynamically spontaneous electron transfer occurs from sulfur ions on the surfaces of the QDs (radius = 1.6 nm) to adsorbed TCNQ molecules and creates indefinitely stable ion pairs that are characterized by steady-state visible and mid-infrared absorption spectroscopy of reduced TCNQ and by NMR spectroscopy of the protons of oleate ligands that coat the QDs.

Dual-time scale photoinduced electron transfer from PbS quantum dots to a molecular acceptor.

A combination of picosecond and microsecond transient absorption dynamics reveals the involvement of two mechanisms by which 1,4-benzoquinone (BQ) induces the decay of the excited state of PbS quantum dots (QDs): (i) electron transfer to BQ molecules adsorbed to the surfaces of PbS QDs and (ii) collisionally gated electron transfer to freely diffusing BQ. Together, these two mechanisms quantitatively describe the quenching of photoluminescence upon addition of BQ to PbS QDs in dichloromethane solution. This work represents the first quantitative study of a QD-ligand system that undergoes both adsorbed and collisionally gated photoinduced charge transfer within the same sample.

Gating of hole transfer from photoexcited PbS quantum dots to aminoferrocene by the ligand shell of the dots.

Photoinduced hole transfer from PbS quantum dots (QDs) to aminoferrocene only occurs if the ligand shell of the QD allows aminoferrocene to gain direct access to the inorganic core of the QD; the permeability of the ligand shell is therefore more important than its conductivity in determining the probability of interfacial charge transfer.

Excited-state dynamics and dye-dye interactions in dye-coated gold nanoparticles with varying alkyl spacer lengths.

Gold nanoparticles (ca. 3 nm in diameter) coated with bis(diarylamino)biphenyl-based thiols with two different alkyl spacers (propyl and dodecyl) between the chromophore and the surface-anchoring thiol group have been prepared and characterized with a variety of techniques. The excited-state dynamics of the dyes in close proximity to the nanoparticle surface were studied using the time-correlated single-photon counting technique and near-IR fs transient absorption spectroscopy.

Preparation and characterization of 4'-donor substituted stilbene-4-thiolate monolayers and their influence on the work function of gold.

Self-assembled monolayers of E-stilbene-4-thiolate (SAM1), E-4'-(ethoxy)stilbene-4-thiolate (SAM2), and E-4'-(dimethylamino)stilbene-4-thiolate (SAM3) on Au(111) have been obtained from reaction of ethanol solutions of the corresponding S-acetyl derivatives with gold substrates. A combination of X-ray photoelectron spectroscopy, ellipsometry, and infrared reflection absorption spectroscopy indicates that the monolayers are dense (ca. 3.