Irradiation-initiated monolayer

In practice, however, photolysis of aqueous solutions of [Ru(bipy)3]2+ produces neither hydrogen nor oxygen in the absence of added catalyst, and despite initial claims106 to the contrary, this is also true for irradiation of monolayers of analogous cationic complexes containing surfactant bipyridyl ligands.107"109... 

Figure 33 PSP micrographs of a structured PS film, prepared by partial ablation of the initiator monolayer followed by thermal polymerization at 60°C for 4 h (styrene/toluene 1 1 v/v) (a) micrograph taken at resonance angle of the irradiated areas (48.2°) (b) micrograph taken at resonance angle of the polymer modified areas (55.2°, 15.7 mn PS).

Experiments were conducted in our laboratory to evaluate many of the dynamical expectations for rapid laser heating of metals. One of the aims of this work was to identify those population distributions which were characteristic of thermally activated desorption processes as opposed to desorption processes which were driven by nontbennal energy sources. Visible and near-infrared laser pulses of nominally 10 ns duration were used to heat the substrate in a nonspecific fashion. Initial experiments were performed by Burgess etal. for the laser-induced desorption of NO from Pt(foil). Operating with a chamber base pressure 2 x 10 torr and with the sample at 200 K, initial irradiation of a freshly cleaned and dosed sample resulted in a short time transient (i.e. heightened desorption yield) followed by nearly steady state LID signals. The desorption yields slowly decreased with time due to depletion of the adsorbate layer at the rate of ca. 10 monolayer... 

The functionalization of H—Si(l 11) surfaces has been extended to the reaction with aldehydes. Indeed, H—Si(lll) reacts thermally (16 h at 85 °C) with decanal to form the corresponding Si—OCH2R monolayer that has been characterized by ATR-FTIR, XPS and atomic force microscopy (AFM) [63]. The reaction is thought to proceed either by a radical chain mechanism via adventitious radical initiation or by nucleophilic addition/hydride transfer. On the other hand, the reaction of H—Si(lll) with octadecanal activated by irradiation with a 150W mercury vapour lamp (21 h at 20-50 °C) afforded a R... 

In contrast to the mixed monolayer, a single monolayer could be used provided that the initiator was not very efficient. AIBN is an excellent choice due to its low molar absorptivity and a long half-life therefore, the initiator will still be present after an initial period of irradiation when the first brush is deposited. The substrate could then be cleaned and reintroduced to a new monomer solution to yield a mixed brush. Both thermal and photochemi-... 

MIP films, applied to a QCM transducer, have been employed for chiral recognition of the R- and 5-propranolol enantiomers [107]. MIP films were prepared for that purpose by surface grafted photo-radical polymerization. First, a monolayer of 11-mercaptoundecanoic acid was self-assembled on a gold electrode of the quartz resonator. Then, a 2,2 -azobis(2-amidinopropane) hydrochloride initiator (AAPH), was attached to this monolayer. Subsequently, this surface-modified resonator was immersed in an ACN solution containing the MAA functional monomer, enantiomer template and trimethylolpropane trimethacrylate (TRIM) cross-linker. Next, the solution was irradiated with UV light for photopolymerization. The resulting MIP-coated resonator was used for enantioselective determination of the propranolol enantiomers under the batch [107] conditions and the FIA [107] conditions with an aqueous-ACN mixed solvent solution as the carrier. The MIP-QCM chemosensor was enantioselective to 5-propranolol at concentrations exceeding 0.38 mM [107]. 

Figure 9.3 Initial CO flux, proportionate to the photodissociation cross section, for irradiation of a monolayer of OCS on smooth, Ag(l 11) and roughened silver surfaces. Reprinted figure with permission from Ref [26]. Copyright 1981 by the American Institute of Physics.

Absj is shown), demonstrating that the monolayer was in-plane optically isotropic at that time. The UV-induced dichroism could be erased on irradiation with unpolarized blue light upon which the initial spectra for both Abs/v and Abs were recovered. Further irradiation with linearly polarized UV light restores the initial dichroism, and successive cycles of UV (linearly... 

In an elegant experiment, Niwa and coworkers prepared a mixed monolayer by codepositing asymmetrical disulphides 14 and 15 in the ratio 200 1. The xanthate groups in disulphide 15 serves as a photo-initiator. Irradiation of the film results in the polymerization of the styrene moieties as seen by cyclic voltammetry. Virtually no polymerization occurs in the single-component monolayer of 14, which proves the importance of having a photo-initiator in the film346,347. 

Other examples of photo-induced transformations in monolayers include reduction of p-nitrothiophenol assembled on a silver electrode to p-aminothiophenol initiated by laser radiation (monitored by SERS)350. UV irradiation of a monolayer terminated with aryl azide in the presence of amines results in incorporation of the amines in the monolayer as azepines and hydrazines. No surface attachment takes place without irradiation, and this makes it a convenient method to prepare photopattemed monolayers351. 

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