No description available.

No description available.

No description available.

Naphthoxazine-spiro-indolines (NOSIs) can exist in a colourless and a coloured form. These compounds can interconvert between these two forms either photochemically or thermally and are resilient to degradation even after repeated cycles of colouration and bleaching. Absorption spectra of both the stable colourless form and the energetically less stable coloured form have been measured. Several NOSI compounds have been shown to photoconvert to the coloured form with an efficiency of between 0.06–0.74, depending upon the compound conditions under which the conversion is brought about. The factors which have been varied in this work are: the basicity of the 6'-substituent; the size of the N-alkyl group within these compounds; and the nature solvent or matrix in which the reaction occurs. Electron donation from the 6'-group has been shown to increase the quantum yield of the forward reaction whereas solvent polarity increases have been shown to reduce the quantum yield.

No description available.

No description available.

Through the use of laser flash photolysis and product studies, the photochemistry of dibenzyl ketone and its derivatives in SDS micelles shows that these aggregates impart some constraint on the dynamics of benzylic radical pairs. The enhancement of the geminate/cross-termination product occurring within the micellar interior is termed the geminate cage effect. Under conditions where all radicals exit from the supramolecular system, a substantial amount of the cross-termination product is observed in the product studies. This experimental evidence cannot be explained with conventional models, and a new proposal is put forth which suggests that some of the cross-termination product arises from radicals that exit the micelle and then recombine upon re-entry. This new approach is based on the binding of solutes to the micelle and is called the partition effect. Two sizes of DODAC vesicles were investigated. In small unilamellar vesicles with a diameter of 30 nm, the cage effect derived from product studies showed a significant enhancement of the cross-termination product. Time-resolved experiments showed that all radicals separate, which implies that all of the enhanced cross-termination reactions from the product studies are derived from random radical encounters. Product studies in large vesicles (∼150 nm diameter) demonstrated that the cross-termination product is enhanced, but not to the same extent as for SDS micelles or small vesicles. Calculations reveal that a significant proportion of the random encounters occur in the bulk aqueous phase. The proposed model suggests that it is not necessary to generate a triplet radical pair in order to observe a magnetic field effect on product distribution. In summary, this new proposal predicts that magnetic field effects in biological systems can be observed as long as mobility between different solubilization sites occurs. / Graduate

No description available.

Thesis (Ph. D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xxviii, 310 p.; also includes graphics (some col.) Includes bibliographical references (p. 181-183). Available online via OhioLINK's ETD Center

Studies have been carried out investigating the photochemical and photophysical properties of anthracene adsorbed on silica gel. The photochemistry and photo physics of anthracene in solution are well reported and known, hence its choice as a probe for the silica gel surface. UV -visible absorption and fluorescence spectra of anthracene adsorbed on silica gel reveal aggregate formation at very low loadings (1 % of a monolayer) indicating preferential adsorption occurs at some surface sites. Laser flash photolysis at 355 nm produces both the triplet and radical cation of anthracene, their production was found to be mono- and multi-photonic respectively. The decays of both these transients were complex and the rates increased with increasing loading. Analysis of the triplet state decay has been carried out by studying the delayed fluorescence which arises from triplet triplet annihilation. Fractal and twodimensional models have been used to describe this bimolecular decay. The coadsorption of anthracene and an electron donor having an oxidation potential below 1.09 V on silica gel causes electron transfer to occur from the electron donor to the anthracene radical cation produced following laser flash photolysis at 355 nm. Studies using a selection of electron donors with varying reduction potentials were carried out. The electron donor transfers an electron to the anthracene radical cation, thus greatly accelerating its rate of decay; for electron donors such as triphenylamine, N,N-dimethylaniline and N,N,N',N'tetramethyl- l,4-phenylenediamine the rise of the donor radical cation is observed as the anthracene cation decays. These systems were studied using fluorescence measurements and laser flash photolysis to study any fluorescence quenching and the rate of decay of both the anthracene triplet and radical cation. A selection of anthracene derivatives adsorbed onto silica gel were also briefly studied to see the effect of substituent group and its position. Symmetrically substituted dialkoxyanthracenes and 9-cyanoanthracene were used. The transient absorption spectra of the 2,3- and 2,6-dialkoxyderivatives and 9-cyanoanthracene revealed spectral similarities with that of unsubstituted anthracene. The spectra of9,10- and I,S-didecyloxyanthracene showed significant differences in the radical cation spectra to those obtained for unsubstituted anthracene.