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1. Weston D.P.,Harris S.J.,Shipway P.H., Weston N.J., Yap G.N. // Trans. Inst. Met.Finish. 2010. V.

88. P. 47.

2. Tsyntsaru N., Cesiulis H., Donten M., Sort J., Pellicer E., Podlaha-Murphy E.J. // Surf. Eng. Appl.

Electrochem. 2012. V. 48. P. 491.

3. Eliaz N., Gileadi E. // Modern Aspects of Electrochemistry. 2008. V. 42. P. 191.

( 11.817.05.05 .

RELATIONSHIP BETWEEN THE MOLECULAR STRUCTURES AND

SPECTROSCOPIC AND ELECTROCHEMICAL PROPERTIES OF PORPHYRINOIDS

Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan, e-mail: nagaok@m.tohoku.ac.jp In tetraazaporphyrin (TAP) compounds such as phthalocyanines (Pcs), naphthalo- cyanines (Ncs), and anthracocyanines (Acs), radial expansion of the -system causes marked red-shifts of the Q absorption bands and negative voltage shifts in the first oxidation potentials, while only minor changes are observed for the first reduction potential. The compounds become steadily more prone to oxidative attack due to destabilization of the HOMO as the molecular size increases with Acs representing the limit for forming stable compounds.

When the symmetry of the -system is lowered, the Q band region of the electronic absorption spectrum is modified substantially. If benzene-ring-fused ZnTAPs are named based on the number of fused benzene rings with Ad and Op denoting adjacent and opposite substitution patterns, respectively, the Q band shifts to longer wavelength in the order 0Zn 1Zn 2AdZn 2OpZn 3Zn 4Zn, where numbers indicate the number of fused benzene unit and Zn means central metal. No splitting is observed in the Q bands of 0Zn, 2AdZn and 4Zn, while those of 1Zn, 2OpZn and 3Zn split into separate x- and y-polarized peaks. The largest Q band splitting is observed in the spectrum of 2OpZn, while the average Q band wavelength lies very close to that of 2AdZn. These spectroscopic properties can be rationalized based on group theory and are reproduced by TD-DFT calculations.

The first oxidation potential shifts to more negative values in the order 0Zn 1Zn 2AdZn~2OpZn 3Zn 4Zn, while the first reduction potential shifts to the negative in the order 0Zn ~ 1Zn ~ 2OpZn 2AdZn ~ 3Zn 4Zn. The HOMO energy appears to be determined by the extent of p-system expansion rather than by the substitution pattern. The first oxidation couples of 2AdZn and 2OpZn differ by only 0.02 V. In contrast, no clear trend is observed in the LUMO energies as the number of fused benzene rings is increased. MO calculations predict that the HOMO is destabilized by p-system expansion and that changes in molecular symmetry destabilize the 1st and 2nd LUMOs in a pattern that closely matches the trends observed in the first reduction potentials. This kind of clear symmetry-potential relationship was elucidated for the first time in chemistry.

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