title: Synthesis, structure, spectral properties and DFT quantum chemical calculations of 4-aminoazobenzene dyes. Effect of intramolecular hydrogen bonding on photoisomerization.
abstract: In this paper three different "push-pull" 4-aminoazobenzene dyes have been synthesized in order to characterize their photochromic behavior in different solvents. The molecular geometry was optimized by DFT/B3LYP functional combined with the standard 6-31+G(d,p) basis set for trans (E) and cis (Z) isomers and the energy levels of HOMO and LUMO frontier orbitals were computed using IEFPCM solvation in CHCl3and DMF. The calculated results were compared to the experimental optical band gap and HOMO values of cyclic voltammetry. The intramolecular six-membered hydrogen bond was formed in both isomers of the synthesized dyes. The thermodynamic parameters such as total electronic energy E (RB3LYP), enthalpy H298(sum of electronic and thermal enthalpies), free Gibbs energy G298(sum of electronic and thermal free Gibbs energies) and dipole moment μ were computed for trans (E) and cis (Z) isomers in order to estimate the ΔEtrans→cis, Δμtrans→cis,ΔHtrans→cis, ΔGtrans→cisand ΔStrans→cisvalues. The NBO analysis was performed in order to understand the intramolecular charge transfer and energy of resonance stabilization. The solvatochromic shift was evaluated by UV-VIS spectroscopy in CHCl3(nonpolar), EtOH (polar protic) and DMF (polar aprotic) solvents to determine the electron withdrawing and donating properties of the substituents on electron transitions energy. Through the increasing solvent polarity a strong bathochromic shift is observed. The photoisomerization experiments have been performed in two solvents CHCl3(nonpolar) and DMF (polar aprotic) by UV light irradiation with λ=365nm at equal concentrations and time of illuminations. The electronic spectra were computed by TD-DFT after geometry optimization using IEFPCM solvation in CHCl3and DMF. The degree of photoisomerization was calculated for the three azo chromophores in both solvents. By using first derivative of the UV-VIS spectra it was possible to resolve the overlapped electron transitions absorption bands. The existing intramolecular hydrogen bond in the azo chromophores was discussed in relation to the isomerization mechanisms and relative stability of the cis (Z) isomers.
authors.affiliation: Department of Organic and Physical Chemistry, 1756 Sofia, 8 St. Kliment Ohridski Blvd, University of Chemical Technology and Metallurgy, Bulgaria. Electronic address: antonchem@abv.bg.
authors.forename: Anton
authors.initials: A
authors.lastname: Georgiev
authors.affiliation: Department of Organic and Physical Chemistry, 1756 Sofia, 8 St. Kliment Ohridski Blvd, University of Chemical Technology and Metallurgy, Bulgaria.
authors.forename: Emil
authors.initials: E
authors.lastname: Bubev
authors.affiliation: Department of Nanostructured Materials and Technology, 1113, Sofia, 109 Acad. G. Bonchev Blvd, Institute of Optical Materials and Technologies, Bulgarian Academy of Science, Bulgaria.
authors.forename: Deyan
authors.initials: D
authors.lastname: Dimov
authors.affiliation: Laboratory of Structural Organic Analysis, Sofia 1113, 9 Acad. G. Bonchev Blvd, Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Science, Bulgaria.
authors.forename: Denitsa
authors.initials: D
authors.lastname: Yancheva
authors.affiliation: Department of Nanostructured Materials and Technology, 1113, Sofia, 109 Acad. G. Bonchev Blvd, Institute of Optical Materials and Technologies, Bulgarian Academy of Science, Bulgaria; Materials Research Centre, Faculty of Chemistry, Purkyňova 118, Brno, Brno University of Technology, Czech Republic.
authors.forename: Ivaylo
authors.initials: I
authors.lastname: Zhivkov
authors.affiliation: Materials Research Centre, Faculty of Chemistry, Purkyňova 118, Brno, Brno University of Technology, Czech Republic.
authors.forename: Jozef
authors.initials: J
authors.lastname: Krajčovič
authors.affiliation: Materials Research Centre, Faculty of Chemistry, Purkyňova 118, Brno, Brno University of Technology, Czech Republic.
authors.forename: Martin
authors.initials: M
authors.lastname: Vala
authors.affiliation: Materials Research Centre, Faculty of Chemistry, Purkyňova 118, Brno, Brno University of Technology, Czech Republic.
authors.forename: Martin
authors.initials: M
authors.lastname: Weiter
authors.affiliation: Department of Organic and Physical Chemistry, 1756 Sofia, 8 St. Kliment Ohridski Blvd, University of Chemical Technology and Metallurgy, Bulgaria.
authors.forename: Maria
authors.initials: M
authors.lastname: Machkova
keywords: 4-aminoazobenzene dyes; DFT quantum chemical calculations; HOMO and LUMO energy levels; Photoisomerization; Solvatochromism; UV-VIS spectroscopy