meta-Photoaddition reactions of 2-chloro-, 2,5-dichloro-, and 2-halo-5-isopropyl-tropones with 9,10-dicyanoanthracene

Photoreactions of 2-halotropones with the excited 9,10-dicyanoanthracene gave a meta-adduct and substitution products occurred at the C-2 position of troponoids. The mechanism of the meta-adduct was proved by the product analysis of the reaction of 3,7-dideuterio-2-bromo-5-isopropyltropone and 9,10-dicyanoanthracene. In the photoreaction of 2-chloro-5-isopropyltropone and 9,10-dicyanoanthracene in a mixed solvent of benzene and methanol, a benzaldehyde with a dibenzo-2-oxabicyclo[3.2.2]nonane system was obtained to support occurrence of an [8+4] cycloaddition reaction between them.     

Spectral Investigations of thf Photoreactions of Flavomononucleotide (FMM) Immoblized in Polymer Film

The absorption, fluorescence and photo-acoustic spectra of flavomonnnucleotide (FMM) molecules embedded in polyvinyl alcohol film were measured for illuminated and for stored in darkness samples. The effect of illumination depends an pigment concentration, and it is connected with FMN excimers formation. The FMN excimer formation prevented the photodestruction of isoatloxazine ring.     

Interaction of triplet-excited benzophenone with hindered amines and amino ethers A laser flash photolysis study employing photoconductivity and light emission measurements

Hindered amines such as 2,2,6,6-tetramethyl piperidines and N-methyl-2,2,6,6-tetramethyl piperidines and hindered amino ethers such as N-methoxy-2,2,6,6-tetramethyl piperidines were examined with respect to their reactivity towards triplet-excited benzophenone (³BP^*) in Ar-saturated acetonitrile solution at room temperature. Upon measuring phosphorescence decay rates in the absence and presence of quencher it was found that the amines are two to three orders of magnitude more reactive than the amino ethers. For all amine/BP systems examined the generation of free ions was inferred from an increase in the electrical conductivity. This indicates that a charge transfer (CT) mechanism is operative in these cases. Notably, tertiary amines were found to be more reactive towards ³BP^* and give higher free ion yields than secondary amines. In the case of amino ether/BP systems evidence for a CT mechanism was not obtained in spite of an increase in the electrical conductivity indicating the generation of free ions. The latter are formed much faster than the phosphorescence decays and very likely originate from triplet–triplet annihilation (³BP^*+³BP^*→BP√⁺+BP√⁻).     

Photoreactions in hydrophobic pockets

Organic chemists have long recognized the important role that reaction media play in controlling rates, product distributions and stereochemistry. Recently, much effort has been directed towards the use of organized media to modify reactivity as compared to that in isotropic liquids. Judicious selection of a given organized system for a given application requires sufficient understanding of the properties of the organized media themselves and those of the substrate interactions therein. The multimolecular aggregation of hydrophobic solutes in water could prove to be of immense value to the organic chemist. The aggregation of simple olefinic systems in water, would enable photocycloaddition to compete efficiently with the various other modes of dacay of the short-lived excited state. Investigations of a few systems (dimerization of coumarins, stilbenes and alkylcinnamates), in our laboratory have been successful and they bring to light the significance of the hydrophobic effect. One of the most accepted manifestations of the hydrophobic interactions is probably the formation of micellar aggregates in aqueous solutions. Micelles provide a unique interface between aqueous and non-aqueous phases at which the non-polar solute can orient itself. While intermolecular orientation at micellar interfaces can provide selectivity in dimerization reactions, intramolecular orientation can be utilized to bring about selectivity in unimolecular photo-transformations. Such examples are presented.