Optical Properties of a Novel Carbon-Carbon Chain Polymer with Pendent Poly(thiophene)s

The synthesis of a novel soluble carbon—carbon chain polymer with pendent terthiophene groups, poly (5-vinyl-2,2\u27:5\u27,2 ‐terthiophene) (PVT), is described. The solvent-cast thing films of PVT display strong blue‐green photoluminescence and, thus, PVT is expected to show electroluminescence in this region. The terthiophene side chains in PVT cross-link when the polymer is oxidized in solution or as thin films with FeCl3 or SbCl5. Based on model studies we have proposed that terthiophene radical cations, initially generated upon doping, slowly couple with neighboring neutral species to yield the radical cations of sexithiophene. The neutralization of the doped polymer with triethylamine yielded an insoluble, cross-linked material. The UV irraditation of thin films of PVT results in cross-linking and insolubilization of the polymer. The mechanism of the photoinitiated cross-linking reaction is discussed

Oxidative Cross-Linking and Grafting of Polymethacrylates with Pendent Thiophene Groups

The absorption spectrum of SbCl5 doped thin films of poly(2-thienylmethyl methacrylate) displays new bands in the visible region attributable to electronic transitions in the radical cation of 2,5\u27-disubstituted bithiophene. Apparently, radical cations of thiophene, initially generated upon doping, rapidly cross-link with neutral thiophenes on neighboring chains. The polymer has been successfully grafted with other thiophene monomers by a similar oxidative coupling reaction. The grafting of side-chain polymers with thiophene and pyrrole monomers could yield new electroactive and nonlinear optical materials

Mechanisms in the Reactions of Arenediazonium Cations with 2-Nitropropanide Anion

Lithium 2-nitropropan-2-ide reacts, in MeOH solvent, with benzenediazonium and p-methoxybenzenediazonium cations to give diazo-coupled products, but with p-nitrobenzenediazonium cation by competing electron transfer and diazo-coupling reactions

Selectivities in Biomimetic Atom Abstraction Reactions

Selectivities of oxometalloporphyrin complexes towards hydrogen atom abstraction from substituted toluenes decrease in the order Cr = O \u3e Fe = O \u3e Mn = O, which is in accord with the force constants of the M = O bonds in these model oxygenases

Mechanisms in a Biomimetic Hydroxylation of a Chemical Probe - 5-Nitroacenaphthene

5-Nitroacenaphthene is hydroxylated by oxometalloporphyrin complexes of chromium, iron, and manganese via hydrogen atom abstraction pathways with charge separation in the transition state dependent on the electrophilicity of the oxygen atom in these model oxygenases

Inverted Regioselectivities in the Reactions of Chlorine Atoms with Heteroarylmethanes

The relative reactivities of the two methyl groups of 2,6-dimethylquinoline (2,6-DMQ) and 2,7 dimethylquinoline (2,7-DMQ) toward several radicals were assessed by intramolecular competitions. The regioselectivities observed for t-BuO· and Br· (k6/k2, k7/k2 \u3e 1) are consistent with electrophilic characteristics of these radicals and estimates of relative stability of the resulting radicals. In contrast, Cl· displays inverted selectivities (k6/k2, k7/k2 \u3c 1) suggesting a directive effect of the DMQ nitrogen. Complexation of Cl· by the N lone pair of dimethylquinolines, followed by a novel intramolecular hydrogen abstraction through a 5-center cyclic transition state, explains the regioselectivities observed in these reactions. Although bromine atoms also complex with heteroaromatics, the Br· complexes have a low reactivity toward benzylic hydrogens. Evidence from intermolecular competition experiments, lasr flash photolysis studies, semiempirical MO calculations, and dimethylbutane quenching experiments is presented in support of the proposed intramolecular hydrogen abstraction process

Electronic-Transitions in Polarons and Bipolarons of Poly(P-Phenylene) Oligomers

The electronic transitions in radical ions (polarons) and dications (bipolarons) of oligomers of poly(p-phenylene) have been measured by laser flash photolysis and steady-state techniques. Plots of the electronic absorption band energies for the polaron and bipolaron are found to be linear functions of inverse chain length. The predicted transitions in the polaron of poly(p-phenylene) (PPP), obtained from extrapolations of these plots to infinite chain length, are considerably lower in energy compared to those reported in doped PPP. Interestingly, the transitions observed by us in the radical ions of p-quaterphenyl and p-sexiphenyl are similar to those observed in highly conducting doped PPP. We have proposed that the polaron is localized to a short segment (n approximately 4-6, where n is the number of phenyl repeat units) of the polymer chain. On the basis of these results, we have concluded that diamagnetic pi-stacks of fairly localized polarons could be the conducting entities in doped PPP