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    Dipolar Ferrocene and Ruthenocene Second-Order Nonlinear Optical Chromophores: A Time-Dependent Density Functional Theory Investigation of Their Absorption Spectra
    (Amer Chemical Soc, 2013) Salman, Seyhan; Bredas, Jean-Luc; Marder, Seth R.; Coropceanu, Veaceslav; Barlow, Stephen
    The origin of the two prominent solvatochromic near-UV/visible/near-IR absorptions observed for donor-(pi-bridge)-acceptor chromophores with ferrocene donors has been investigated using TD-DFT methods. Both chromophores with relatively weak (4-nitrophenyl) and strong acceptors (1,3-diethyl-2-thiobarbituric acid and 3-dicyanomethylidene-2,3-dihydrobenzothiophene-1,1-dioxide) were considered, as were ferrocene and octamethylferrocene donors. Computational predictions of optical properties made using the B3PW91 functional were found to be in good agreement with experimental data. The calculations reveal a complex orbital picture that varies from compound to compound, contribution of multiple configurations to some of the important states, and significant contributions from more than one transition to the experimentally observed bands. Natural transition orbitals have been used to gain an understanding of the charge redistribution associated with the transitions. The relatively weak low-energy bands of the ferrocene derivatives were generally found to have both d-d and metal-to-pi-bridge/acceptor charge-transfer character. The stronger higher energy bands were found to be associated with charge transfer from cyclopentadienyl rings and the pi bridge toward the acceptor group. The experimental spectra of ruthenocene chromophores differ significantly from those of the analogous ferrocene chromophores; however, the calculations reproduce the key differences and indicate a similar origin for the contributing transitions.
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    How substitution tunes the electronic and transport properties of oligothiophenes, oligoselenophenes and oligotellurophenes
    (Elsevier Science Sa, 2015) Erbay, Tugce Gulsen; Aviyente, Viktorya; Salman, Seyhan
    The geometrical, electronic and charge-transport properties of a series of unsubstituted and dicyanovinyl (DCV)-substituted oligothiophenes (nT), oligoselenophenes (nS) and oligotellurophenes (nTe) where n = 3-5 are investigated by means of Density Functional Theory (DFT) and Time-Dependent DFT calculations. The intramolecular reorganization energy is found to decrease upon dicyanovinyl substitution, with a larger decrease for holes than electrons. The ground state HOMO and LUMO energies along with the Time-Dependent DFT calculations show smaller HOMO-LUMO gaps for the DCV-substituted oligomers. Calculations of the intermolecular charge transfer integrals in the crystals have been performed to understand the role of substitution on the charge-transport rate. DCV-substitution changes the packing motifs in the crystal and results in larger transfer integrals for holes along the pi-stacldng direction, calculated as -63 and -88 meV for DCV4T and DCV4S respectively. These results suggest that DCV-substituted oligomers studied here are more promising charge transporting materials than their unsubstituted analogues. (C) 2015 Elsevier B.V. All rights reserved.
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    A Microwave Ring Resonator Based Glucose Sensor
    (Elsevier Science Bv, 2016) Camli, Berk; Kusakci, Emre; Lafci, Berkan; Salman, Seyhan; Torun, Hamdi; Yalcinkaya, Arda
    A microwave ring resonator based glucose detecting biosensor incorporating glucose oxidase enzyme is presented. Sensor uses a split ring resonator as a transducer, where the sensing operation is done by the observation of shifts in its resonant frequency. Resonator was fabricated with basic fabrication techniques and the enzyme was immobilized via conductive polymer agent PEDOT: PSS. Experimentally observed redshift of resonant frequency of the sensor in response to different loading conditions are in agreement with simulation results and theoretical expectations. Sensor selectivity is confirmed with control experiments conducted with NaCl solutions. Experiments done with different glucose solution concentrations yielded a sensor sensitivity of 0.174MHz/mgml(-1). (C) 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.