Free radicals generated by decomposition of benzoyl peroxide in the presence of alkyl iodides have been used to derivatize small-diameter single-wall carbon nanotubes (HiPco tubes). The degree of functionalization, estimated by thermal gravimetric analysis, is as high as 1 in approximately 5 carbons in the nanotube framework. The derivatized nanotubes exhibits remarkably improved solubility in organic solvents. The attached groups can be removed by heating in an atmosphere of argon. Derivatization was also accomplished by treating SWNTs with various sulfoxides employing Fenton's reagent. [reaction: see text]

Photosensitized oxidation of trans,, trans-stilbene (TS), and 2,3-dihydro-γ-pyran (DHP) included in the internal framework of Na-ZSM-5 zeolites was investigated. The zeolite samples having adsorbed the alkenes were suspended in isooctane or pentaerythritol trimethyl ether (PTE), and the sensitizers, 9,10-dicyanoanthracene (DCA) and hypocrellin A (HA), were dissolved in the solution. The molecular sizes of both of the sensitizers and the solvents are greater compared with the channels of the zeolites. The isolation of the alkenes within the zeolites from the sensitizers in surrounding solution prevents them from undergoing electron transfer. On the other hand, singlet oxygen was produced in the solution and diffused into the internal framework of the zeolites to react with the alkenes. Thus, only singlet oxygen oxidation products were obtained and no product derived from superoxide radical anion was detected. By addition of water after the alkene adsorption, the photosensitized oxidation product distributions can be dramatically varied depending upon the aluminum content of the zeolite framework and the molecular dimensions of the substrates. Possible interpretations of these effects are discussed in terms of the locations of the reactants.

This paper presents results of the synthesis and photophysical study of N-(1-pyrenylmethyl)-2‘-deoxyuridine-5-carboxamide (PMA-dU) and its spectroscopic model N-acetyl-1-aminomethylpyrene (PMA-Ac). The goal in these studies is to learn about the intrinsic forward and reverse electron-transfer (ET) processes in the PMA-dU nucleoside as a means of developing pyrenyl-dU nucleosides with ET product lifetimes in the 0.5 ns time range. Absorbance and emission spectra, emission quantum yields, and emission lifetimes are reported for both compounds in three solvents. The data show that the emission yield quenching varies from 75 to 98% in the solvent series THF, MeCN, and MeOH. Pyrenyl (π,π*) emission quenching is assigned to ET that forms the pyrene•+/dU•- product as observed previously in other pyrenyl-dU nucleosides. In contrast to the monoexponential emission decay of PMA-Ac, the emission of PMA-dU at all wavelengths is multiexponential with 4 lifetimes in THF and nearly always with 3 in MeCN and MeOH. The multiexponential decay is likely due to the presence of multiple nucleoside conformers. Importantly, the emission decay for the nucleoside in the 500−550 nm region is assigned to relaxation of the pyrene•+/dU•- ET product. The 0.5−4 ns time range contains over 95% of the emission amplitude in this wavelength region for the polar solvents MeCN and MeOH. Thus, the ET product in PMA-dU appears to have the desired long lifetime. Additionally, CIS INDO/S computations of the excited-state properties of 19 conformers of the nucleoside model N-(1-pyrenylmethyl)-1-methyluracil-5-carboxamide (PMA-UMe) identify two key factors that control the energy of pyrene•+/dU•- ET products. One is ease of reduction of the uracil subunit, in turn controlled by variation of the angle between the uracil-C5 carbonyl and the plane of uracil (R = 0.90). The other is Coulombic attraction between the pyrenyl cation and uracil anion subunits. The Coulombic and CO/UMe dihedral angle contributions to the energy of the ET1 state are independent of each other and can operate either in or out of phase with respect to varying energy of the ΕΤ1 state.