Peripheral and structural effects on the band gap of acceptor-donor type conducting polymers containing pendant bisfulleroid groups

In this computational study, the band gap energy of an acceptordonor type conducting polymer consisting of terthiophene repeating units with a fused bisfulleroid group was estimated by extrapolating excitation energies approximated by the HOMO-LUMO energy differences as well as the TDDFT method with respect to the inverse number of monomer units.Optimizations were performed both in vacuum and in o-dichlorobenzene (as solvent) using the B3LYP and MPW1B95 functionals.The calculated optical band gap was found to be in good agreement with experimentally reported band gaps in the literature. However, different band gaps with different experimental techniques were reported in the referred experimental study for the same system. To understand the reasons behind this behavior, effects of the structural (inter- and intramolecular stacking) and environmental (explicit and implicit solvation and acidic doping) factors on the absorption of the terthiophene monomer with fused bisfulleroid were investigated. Acid doping was found to be very important in terms of the present system

Effect of cooperative hydrogen bonding in Azo-Hydrazone Tautomerism of Azo Dyes

Azo-hydrazone tautomerism in azo dyes has been modeled by using density functional theory (DFT) at the B3LYP/6-31+G(d,p) level of theory. The most stable tautomer was determined both for model compounds and for azo dyes Acid Orange 7 and Solvent Yellow 14. The effects of the sulfonate group substitution and the replacement of the phenyl group with naphthyl on the tautomer stability and on the behavior in solvent have been discussed. Intramolecular hydrogen bond energies have been estimated for the azo and hydrazone tautomers to derive a relationship between the tautomer stability and the hydrogen bond strength. The transition structures for proton transfer displayed resonance assisted strong hydrogen bonding properties within the framework of the electrostatic-coValent hydrogen bond model (ECHBM). Evolution of the intramolecular hydrogen bond with changing structural and environmental factors during the tautomeric conversion process has been studied extensively by means of the atoms-in-molecules (AIM) analysis of the electron density. The bulk solvent effect was examined using the self-consistent reaction field model. Special solute-solvent interactions were further investigated by means of quantum mechanical calculations after defining the firstsolvation shell by molecular dynamics simulations. The effect of cooperative hydrogen bonding with solvent molecules on the tautomer stability has been discussed