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The stability of superoxide ion (O(2)(*-)) generated chemically by dissolving KO(2) in dried dimethyl sulfoxide solutions containing imidazolium cation [e.g., 1-ethyl-3-methylimidazolium (EMI(+)) and 1-n-butyl-2,3-dimethylimidazolium (BMMI(+))] based ionic liquids (ILs) was investigated with UV-visible spectroscopic, NMR, and voltammetric techniques and an ab initio molecular orbital calculation. UV-visible spectroscopic and cyclic voltammetric measurements reveal that the O(2)(*-) species reacts with BMMI(+) and EMI(+) cations of ILs to form hydrogen peroxide. The pseudo first order rate constant for the reaction of BMMI(+) and O(2)(*-) species was found to be about 2.5 x 10(-3) s(-1). With a molecular orbital calculation, the O(2)(*-) species is understood to attack the 2-position (C-2) of the imidazolium ring (i.e., BMMI(+)) to form an ion pair complex in which one oxygen atom is bounded to C-2 and the other to the hydrogen atom of -CH(3) group attached to C-2. Eventually, the ion pair complex of BMMI(+) cation and O(2)(*-) species undergoes a ring opening reaction as evidenced with (1)H NMR measurement.

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A series of new poly(aryleneethynylene)-type π-conjugated copolymers, which consist of an electron-accepting 1,3,4-thiadiazole, 4-alkyl-1,2,4-triazole, or 3,4-dinitrothiophene unit and an electrondonating 1,4-didodecyloxybenzene or N-dodecylpyrrole unit, were prepared in 81-93% yields by palladiumcatalyzed polycondensation. Their related model compounds (PhC≡C-Ar-C≡CPh; Ar ) the electronaccepting unit) were also synthesized. GPC traces of the polymers gave number average molecular weights (M n's) of 6900-29 700. The polymers formed a molecular assembly and a birefringent phase as revealed by powder X-ray diffraction (XRD) analysis and polarized light optical microscopy (POM). They formed an aligned structure on a platinum plate. The UV-vis peaks of the polymers appeared in the range of 385-522 nm in solutions, and the peak was shifted by 10-44 nm to a longer wavelength in films, according to intermolecular electronic interaction. The density functional theory (DFT) calculations supported the presence of strong intermolecular interaction between the polymer molecules. The polymers composed of a 1,3,4-thiadiazole or a 1,2,4-triazole unit exhibited photoluminescence with quantum yields of about 50% in chloroform. The polymers were electrochemically active and showed the reduction peak in a range of -1.1 through -2.2 V vs Ag + /Ag.

No abstract

New alternating donor-acceptor charge-transfer (CT)-type copolymers consisting of didodecyloxy-p-phenylene (Ph), N-(4-dodecyloxyphenyl)carbazole (Cz), or N-hexyldiphenylamine (Da) unit (π-electron donor) and 2,1,3-benzoselenadiazole (BSe) unit (π-electron acceptor) were prepared by palladium-catalyzed Suzuki coupling reaction in 85-96% yields. The copolymers with the Ph and Cz units were soluble in common organic solvents and gave number-average molecular weights of 8300 and 6600, respectively, in GPC analysis; the copolymer with the Da unit was partly soluble in the solvents. The UV-vis absorption peak of the polymers appeared in the range of 420-530 nm in solutions and films, and the optical transition is considered to be accompanied by CT from the donor unit to the BSe unit. Quantum-chemical calculations of a trimeric model compound (Ph-BSe-Ph: 10) supported the notion that the optical activation of the copolymer involved the CT process. Cyclic voltammetry revealed that the copolymers were susceptible to both electrochemical oxidation and reduction, and they had a LUMO level ranging from -3.08 to -2.91 eV and a HOMO level ranging from -5.56 to -5.12 eV. Comparison of the electronic effect of the BSe unit with that of a 2,1,3-benzothiadiazole unit is discussed.

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Two-dimensional (2D) arrays of poly(γ-n-alkyl l-glutamates) (PG n ) on HOPG are found to be formed by casting under conditions producing submonolayer coverage. Direct observation of the arrays in a series of polymers using atomic force microscopy allowed clear visualization of the island structures, which consisted of parallel running rods. The helical polymer chains were epitaxially aligned to form rods with a “head to head” or a “head to tail” association. In the array composed of rods, the extended alkyl side chains with all-trans conformation are divided to both sides of a helical main chain and align perpendicularly to the main chain. The interval distances between parallel rods in the island increased linearly by about 2.2 Å/CH2 unit with increasing alkyl side chain length. Epitaxial adsorption of alkyl chain moieties onto graphite is the primary driving force in the formation of the 2D array structure of these helical polymers.