XII Iberian Meeting of Electrochemistry XVI Meeting of the ...

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XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society O E 01 Electrochemistry of Push-Pull compounds based on Quinoline-N-Oxide C. Capel Ferrón a,b , B. Vercelli b , G. Zotti b , J. M. Montenegro c , E. Pérez Inestrosa c , V. Hernández a , J. T. López Navarrete a a Department of Physical Chemistry, Málaga University, 29071 Málaga (Spain) b Institute for Energetics and Interphases-IENI CNR, C.so Stati Uniti, 4, 35127 Padova (Italy) c Department of Organic Chemistry, Málaga University, 29071 Málaga (Spain) capel@uma.es Dipolar push-pull chromophores are currently the subject of great interest for their use in photonic devices and represent the widest class of organic compounds investigated for their nonlinear optical (NLO) properties [1] and rectifying behaviour in molecular electronics. [2] Push-pull NLO systems are basically constituted by an electron-donor (D) and an electron-acceptor (A) group interacting though a -conjugated spacer (S) (D-S-A molecules). These systems constitute the way to achieve an efficient charge redistribution from the donor to the acceptor end groups. Here we consider a series of D-S-A molecules based on quinoline-N-oxide (A) moieties The UV-Vis absorption spectra in acetonitrile of 1-3 upon addition of acid (HClO 4 ) increase in intensity and maxima are largely batochromically shifted, due to protonation of the N-oxide moiety which increases its acceptor ability. Further addition of HClO 4 to solutions of 2 and 3 causes a subsequent hypsochromic shift due to the protonation of the methoxy or dimethylamino electron-donor groups. The reduction potential of aromatic N-oxides is known to be strongly pH-dependent, reduction being facilitated under acidic conditions and the protonated N-oxide becoming a much better electron acceptor. In this regard, we have investigated the electrochemistry of both the neutral and protonated forms of all these D-S-A chromophores, together with the complexation of 3 with a Lewis acid like zinc chloride. References [1] Prasad, P. N.; Wiliams, D. J. Introduction to Nonlinear Optical Effects in MolecVles and Polymers; Wiley: New York, 1991 [2] (a) Geoffrey J. Ashwell,* Wayne D. Tyrrell, Anne J. Whittam, J.Am.Chem. Soc. 2004, 126, 7102; (b) Geoffrey J. Ashwell, Anna Chwialkowska, Chem. Commun., 2006, 1404. September, 811, 2010. ISEL - Lisbon 50
XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society O E 02 Electrochemical, Thermodynamic and K inetic Studies of the Acylated Cyanoimido-Complexes trans- Mo(N C N){N C N C(O)R}(dppe) 2 Cl Elisabete C.B.A. Alegria, a,b M. Fátima C. Guedes da Silva, b,c Maxim L. Kuznetsov, b Luísa M.D.R.S. Martins, a,b Armando J.L. Pombeiro b a Área Departamental de Engenharia Química, ISEL, R. Conselheiro Emídio Navarro, 1959-007 Lisbon, Portugal b Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, TU Lisbon, Av. Rovisco Pais, 1049001 Lisbon, Portugal c Universidade Lusófona de Humanidades e Tecnologias, ULHT Lisbon, Av. do Campo Grande, 376, 1749-024 Lisbon, Portugal ebastos@deq.isel.ipl.pt The electrochemical behaviour of the complexes trans- Mo(NCN){NCNC(O)R}(dppe) 2 Cl (R = Me, Et and Ph) (denoted by A + ) has been investigated by cyclic voltammetry (CV) and controlled potential electrolysis (CPE) in aprotic medium, at a Pt electrode. These complexes exhibit, apart from a partially reversible oxidation attributed to the Mo(IV) to Mo(V) oxidation, a first partially reversible reduction (A + to A 0 ) process which involves a electron-transfer-induced rearrangement according to the indicated ECEC square-type Scheme (Figure). Digital simulation of the cyclic voltammetric data, at a range of scan rates, allows to estimate the corresponding equilibrium and rate constants. Theoretical calculations were also performed on attempting to identify the electrochemically generated species B. A + e A k2 K 1 = k 1 / k -1 k-2 k -1 k 1 K 2 = k 2 / k -2 B + - e B Acknowledgments: This work has been partially supported by the IPL/41/2003 project, the Fundação para a Ciência e Tecnologia (F CT), the POCTI (F EDER funded) and the PRODEP programmes. References 1 S.M.P.R.M. Cunha, M.F.C. Guedes da Silva, A.J.L. Pombeiro, J. Chem. Soc., Dalton Trans., 2002, 1791 2 A.J.L. Pombeiro, M.F.C. Guedes da Silva, M.A.N.D.A. Lemos, Coord. Chem Rev., 2001, 219. [3] M.L. Kuznetsov, A.J.L. Pombeiro, J. Chem. Soc., Dalton Trans., 2003, 738. September, 811, 2010. ISEL - Lisbon 51
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