Pattern formation photochemical

Yasushi, O., Y. Shoji, and K. Masaki, 2004. Metal pattern formation by selective electroless metalli2ation on polypyrrole films patterned by photochemical degradation of iron (P) chloride as oxidizing agent. Synth Met 144 265. 

MULLER - Do you think that this photochemically bistable system is a candidate for spatial pattern formation (without convective effects) under externally homogeneous illumination with the appropriate wavelength The chemical "feed-back loop" combined with diffusive transport might constitute a source of spatial symmetry-breaking, e.g. in an extended solution layer. 

Frdns has demonstrated this possibility with reserpine and rescinnamine hy irradiating at the start zone for two hours and obtaining a characteristic zone pattern (fingerprint) after TLC separation of the photochemically produced derivatives [20J. Huck and Dworcak exposed developed chromatograms with vanilmandelic acid and homovanillic acid zones to diffuse daylight and observed the formation of fluorescent metabolites that were suitable for direct quantitative analysis [21]. 

The most important photochemical reaction of carbon to carbon unsaturated carbohydrates is addition to the unsaturated system. Two types of addition reaction are readily recognized. The first consists of those in which the molecule adding to the carbohydrate does so by involving a 77-bond of its own. Processes of this type, listed in Table I, are those which lead to formation of a new ring-system (cycloaddition). The second class of addition reaction is one in which a cr-bond is broken in the molecule adding to the unsaturated carbohydrate. The reactions that belong to the latter category (see Tables II and III) follow two basic patterns, and comprise the majority of the addition processes reported. 

It is pertinent to mention the formation of y-ketols by photochemical addition of alcohols to enones follows the same polarity pattern [193],... 

The example just cited provides a verification of the prediction that the excited-state reactions should be conrotatory for six-electron systems. The prototype octatriene-cyclohexadiene interconversion (Equation 12.64) shows the same pattern.117 The network of photochemical and thermal electrocyclic reactions connected with the formation of vitamin D provide several further examples.118... 

Figure 1 Formation of a holographic grating. Crossed laser beams create a sinusoidal intensity pattern recorded in the film through photochemical processes.

Ti02 nanocrystalline substrate have new potential applications such as photolithography (nanowriting) - formation of conducting patterns in chips or integrated circuits. In these systems a photochemical reaction is limited to the size of the semiconductor particle. Thus, the metallic conductor size can be obtained in the nanometer size regime [27]. 

An exceptional case of ring formation and cleavage deals with a system incorporating two cyclopropane units with donor-acceptor pattern. Photochemical synthesis of 94 and electrocyclic reaction afford the unusual bridged hexanooxepin 9554). 

In photochemical reactions, the population of excited states of different orbital origins can result in quite different reactivity patterns. Therefore, reaction products may occur, which are not accessible at all in thermochemical pathways. Especially in organometallic and coordination compounds, the primary photoproducts obtained are not always resulting from the lowest-lying excited state levels. Wavelength-selective excitation may then be exploited to channel the product formation process and to control a possible branching between different reactivity patterns. 

Tandem fragmentation-cyclization of bicyclic ketones connected to unsaturated side chains have been used to construct hi-, tri-, and spirocyclic ketones [334], Cossy et al. have shown that depending upon the substitution pattern, ketyl radical anions obtained from photochemically induced electron transfer from amines to cyclopropylketones lead either to the formation of 3-substituted cycloalkanones or to ring expanded products (Scheme 78) [335],... 

The reactions of diphenylmethylene and fluorenylidene with olefinic double bonds are not stereospecific. Photochemical or thermal decomposition of diphenyldiazomethane in the presence of alkenes is often accompanied by the formation of a substantial amount of non-cyclic products derived from abstraction-recombination reactions The extent of hydrogen abstraction relative to addition is highly dependent on the substitution pattern of the olefin In contrast, fluorenylidene generated from 9-diazofluorene usually gives cyclopropanes as the major product. Cyclopentadienylidene and its substituted analogues can be generated from the corresponding diazo precursors. They react with olefinic as well as with acetylenic substrates Cycloheptatrienylidene preferentially... 

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