Photocatalytic reduction of an azide-terminated self-assembled monolayer using CdS quantum dots.

Ordered, tightly packed aryl-azide-terminated, self-assembled monolayers (SAMs) were created on gold substrates from a new disulfide precursor. These monolayers were reduced at least partially in an aqueous environment using approximately 2 nm CdS quantum dots (Qdots) as photocatalysts to give mixed monolayers of arylamine- and aryl azide-terminated species. The CdS photocatalysts were made available for the reaction by exposure of the azide-terminated SAM to Qdots initially in solution or by preadsorption of the CdS nanoparticles on the SAM. In either case, X-ray photoelectron spectroscopy (XPS), grazing angle Fourier transform infrared spectroscopy (FTIR), and contact angle measurements were used to show the occurrence of the photocatalytic reduction. As further evidence for the presence of arylamine-terminated thiolate in the reduced SAM, these arylamine groups were successfully tagged with fluorescein isothiocyanate (FITC). The use of Qdot photocatalysts to functionalize surfaces may lead to a means to pattern surfaces at the nanoscale.

Secondary alpha isotope effects on deuterium tunneling in triplet o-methylanthrones: extraordinary sensitivity to barrier width.

The rates of deuterium transfer in the photoenolization of triplet 1,4-dimethyl-10H-anthracen-9-one (1) with varying degrees of deuterium label in their methyl groups (1-d3, 1-d2, and 1-d) have been investigated as a function of temperature between 5 and 77 K. Measurable rate constants in the case of 1-d3 and 1-d2 were used to construct Arrhenius plots which illustrate the expected curvature and leveling off of rate constant versus temperature. The difference in tunneling rate constants of 1-d3 and 1-d2 yields a tunneling isotope effect, TIE = 2.4, which is attributed to the secondary alpha isotopic substitution. Density functional theory (DFT, B3LYP/6-31G*) calculations were carried out to obtain structural and energetic information for the H(D) transfer along the triplet state zero-point energy levels. The temperature dependence of the rate constants for each isotopologue was simulated with a model that considers the frequency of the C-D stretching mode and the quantum mechanical permeability determined from calculated energy parameters. The model suggests that a difference in barrier width of only 0.015 A between 1-d3 and 1-d2 leads to the observed 2-fold difference between tunneling rates.