Nursel Acar

Towards modelling light processes of blue-light photoreceptors. Pyrene–isoalloxazine (flavin)–phenothiazine triad: electrochemical, photophysical, investigations and quantum chemical calculations

The triad 6 containing the phenothiazine–isoalloxazine couple as donor–acceptor redox unit and pyrene as antenna absorbing in the UV-A region has been designed to mimic the light processes of natural photoreceptors. By cyclic voltammetry it is shown that the redox chemistry of the three subunits of triad 6 behave almost independently, indicating no electronic coupling between the subunits in the ground state. Triad 6 exhibits three accessible redox states with one oxidation and two reduction waves due to the formation of the phenothiazine radical cation and isoalloxazine and pyrene radical anions. UV/Vis/NIR spectroelectrochemistry reveals the generation of the protonated isoalloxazine dianion on reduction which is formed in the non-polar solvent in a reduction–protonation–reduction step (two-electron transfer process) and which is attributed to intermolecular proton transfer from the amide group to the electrochemically reduced isoalloxazine radical anion. Evidences for the photoinduced energy and electron transfer within the triad are provided by steady state and time-resolved absorption and fluorescence measurements. Spectroscopic studies displayed that upon excitation the pyrene emission was dramatically quenched in the dyad 4. This is most likely due to the energy transfer from pyrene to the isoalloxazine units as the absorption band of isoalloxazine overlaps with the pyrene emission band leading most likely to a CT state of the isoalloxazine/phenothiazine type. Quenching of the phenothiazine fluorescence in triad 6 was also ascribed to the spectroscopic overlap between the emission spectrum of phenothiazine and absorption spectrum of isoalloxazine. Again, photoinduced electron transfer from phenothiazine to isoalloxazine is expected to be the cause for the quenching of the isoalloxazine emission in the dyad 5. Molecular orbital calculations for compound 5 showed a complete electron transfer from phenothiazin to isoalloxazine.

DFT and TDDFT investigation of the Schiff base formed by tacrine and saccharin

AbstractSchiff bases have many chemical and biological applications in medicine and pharmaceuticals due to the presence of an imine group (−C=N−). These bases are used in many different fields of technology, and in photochemistry because of their photochromic properties. Here, the structural and electronic properties of the Schiff base formed by tacrine and saccharin (TacSac) were explored using density functional theory with the B3LYP, M06-2X, M06L, and ωB97XD functionals in combination with the 6-311++G(d,p) basis set. The time-dependent formalism was used at the B3LYP/6-311++G(d,p) level to obtain electronic transitions. The calculations were repeated in an implicit solvent model mimicking water, using the polarizable continuum model in conjunction with a solvation model based on a density approach. The results indicate that TacSac cannot form spontaneously, but can be obtained in mild reactions. However, the resulting Schiff base displays different characteristics to its monomers. It also has the potential for use in photochemical intramolecular charge-transfer systems. Graphical AbstractIntramolecular charge transfer between HOMO and LUMO of TacSac

Structural, spectroscopic and passivation properties of a novel binuclear clamshell-type zinc(II) phthalocyanine as gate dielectric for OFET

A novel clamshell-type binuclear zinc(II) phthalocyanine (2) was synthesized by cross condensation of the bisphthalonitrile (1) with 4-tert-butylphthalonitrile and zinc acetate in 1:10:4 ratio. The structure of the novel compound was characterized by elemental analysis, UV-vis, FT-IR (ATR), HR MALDI-TOF mass, 1H NMR, 13C DEPT NMR and 1H–1H COSY NMR methods. Applying electronic absorption spectroscopy and density functional theory (DFT) revealed that in THF the geometry of 2 is twisted to adopt an intermediate clamshell conformation in which the spacing between the Zn centers is about 8.1A, providing a very good account of the observed spectrum exhibiting the characteristic B (Soret) band at 347 nm and the Q band at 673 nm. In solution, 2 was found to exist in non-aggregated form. The calculated fluorescence quantum yields (ΦF = 0.23 in THF and 0.10 in DMF) were relatively reduced in comparison to that of std ZnPc. In particular, understanding of leakage current conduction mechanisms in gate dielectrics is...

Computational studies of metal carbonyl complexes of 3[4-ethyl(phenly)imino][indoline-2-one] and 3[4-butyl(phenly)imino][indoline-2-one]

AbstractUse and application of Schiff bases are extended to many different fields of technology. (ISE)M(CO)5 complex [M = Cr (1), Mo (2), W (3), and where ISE is 3[4-ethyl(phenly)imino][indoline-2-one]; and (ISB)M(CO)5 [M = Cr (4), Mo (5), W (6)], where ISB is 3[4-butly(phenly)imino][indoline-2-one] were investigated by computational methods. Computations were carried out using density functional theory (DFT) with B3LYP and CAM-B3LYP functionals, in conjunction with LanL2DZ basis set for metals and cc-PVTZ basis set for other atoms. Time-dependent density functional theory (TDDFT) was used at the same level to obtain the electronic transitions. Molecular orbital energies, UV-Vis spectra, and total electron densities of investigated molecules were shown in the gas phase and in THF. Metal complexes showed higher absorption coefficients compared to ISE and ISB in the visible region. Additionally, they displayed absorption peaks at longer wavelengths and full MLCT character in solution, and W complexes required less energy compared to the complexes of other investigated metal ions. Among the investigated systems, (ISE)W(CO)5 and (ISB)W(CO)5 complexes with lowest HOMO-LUMO gaps are found to be the best candidates for photosensitive material production. Graphical AbstractUV-Vis absorption spectra of ISE and (ISE)W(CO)5