Interactions between n-conjugated molecules in their charged and photozcidec states

+147hlm.;24c

Solvent effects on the π-dimerization of cation radicals of conjugated oligomers

π-Dimerization of cation radicals of conjugated oligomers has been investigated in various solvents to assess the effect of the polarity of the medium on the dimerization enthalpy. It is found that π-dimerization is favored in less polar solvents, unless solubilizing substituents are present

Synthesis and and characterisation of novel regioregular polythiophenes - Tuning the redox properties

The synthesis and full characterisation of three novel regioregular polythiophenes 8, 9, and 15 is presented. By varying the nature of the substituents on the polythiophene backbone in these materials it is possible to increase their first oxidation potential by almost 0.5 V. Because the first reduction potential follows the same trend, the electrochemical band gap of these polymers is essentially constant. The constant band gap inferred from the electrochemical data is confirmed by the onset of the optical absorption spectrum of the polythiophenes, which shows only small changes

Synthesis and characterization of novel regioregular polythiophenes

Three novel regioregular polythiophenes with side chain substituents resulting in increased oxidation potentials relative to poly(3-dodecylthiophene) have been synthesized using the McCullough polymerization protocol. All polymers have >95% head-to-tail couplings as evidenced from 1H-NMR and are furthermore characterized by SEC, solution and solid-state UV-vis spectroscopy, and cyclic voltammetry. By varying the nature of the side chains the redox properties could be altered: the first oxidation potentials vary between 0.75 V and 1.25 V and the first reduction potentials between -1.40 V and -1.85 V. The optical properties of the polymers in solution and as thin solid films were much less affected by the different substituents

Pairwise Gibbs Energies of Interaction Involving N-Alkyl-2-pyrrolidinones and Related Compounds in Aqueous Solution Obtained from Kinetic Medium Effects

Kinetic solvent effects of N-alkyl-2-pyrrolidinones and structurally related compounds on the water-catalyzed hydrolysis reactions of p-methoxyphenyl dichloroacetate (MPDA), 1-benzoyl-3-phenyl-1,2,4-triazole (BPhT), and 1-benzoyl-1,2,4-triazole (BT) in highly dilute aqueous solutions at pH 4 and 298.15 K have been determined by UV/vis spectroscopy. Using a thermodynamic description of solute-solute interactions in aqueous solutions, the kinetic results have been analyzed in terms of pairwise Gibbs energy interaction parameters: G(c) values. These are negative, indicating that hydrophobic interactions in the initial state dominate the medium effects. The interaction parameters increase in the order MPDA<BT<BPhT, suggesting increasing hydrophobic stabilization in the order of MPDA>BT>BPhT. However, when differences in reactivity and transition state effects are taken into account, it appears that BPhT is more successful in establishing hydrophobic interactions with the cosolutes than are MPDA and BT. Using the SWAG-approach for additivity of group interactions, additivity is observed for the first three consecutive CH2 groups in the cosolute in all three hydrolysis reactions. Larger alkyl substituents cause larger retardations than anticipated on basis of this additivity. The results are explained by intramolecular destructive overlap of the polar hydration shell of the amide functionality and the apolar (hydrophobic) hydration shell of the alkyl group, which extends to the third CH2 group in the N-alkyl group of the cosolute molecule. The inner apolar groups, therefore, have a reduced apparent hydrophobicity. More remote CH2 groups develop independent hydrophobic hydration shells. The effect of the position of a CH2 group in the cosolute molecule is also considered. Kinetic solvent effects with structurally related esters show that amide-amide, ester-ester, and amide-ester group interactions affect the transition state in different ways. Finally, the effects of PVP polymers on the three hydrolysis reactions have been examined. The data presented enhance the understanding of pairwise hydrophobic interactions in aqueous solutions. In addition the results provide insights into the interactions between hydrophobic and hydrophilic hydration shells as well as into the energetics of amide hydration and interactions involving amides in aqueous solution, both playing important roles in protein stabilization.

Unexpected Dimerization of Oxidized Fullerene-Oligothiophene-Fullerene Triads

Can bulky fullerene substituents reduce the dimerization tendency of oligothiophene radical cations? These authors prepared the dumbbell-shaped bis-C60-substituted oligothiophene shown in the Figure in order to address this question. Contrary to expectation, the molecules display extensive dimerization, even at room temperature, in remarkable contrast to the corresponding unsubstituted oligothiophenes