Electrochemical and spectroelectrochemical behavior of methyl pheophorbide a - zinc phthalocyanine dyadстатья
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Аннотация:The electrochemical properties of a covalently linked conjugate (Dyad) composed ofmethyl pheophorbide a (Pheo a) and zinc(II) 2-(2-hydroxymethylbenzyloxy)-9(10),16(17),23(24)-tritert-butylphthalocyaninate (ZnPc) were studied. Cyclic voltammetry (CV) and square wave voltammetry(SWV) measurements revealed three reductions at -1.59, 1.78 and -2.03 V vs. Fc+/Fc and four oxidationsat 0.06, 0.47, 0.57 and 0.87 V vs. Fc+/Fc in o-DCB containing 0.05 M TBAPF6. The first reductionincluded two overlapped processes, the reduction of Pheo a followed by the reduction of ZnPc,separated by ca. 0.08 V. Compared to individual components, the ZnPc subunit in Dyad undergoesthe first oxidation more easily with a cathodic shift of potential by 0.08 V, while Pheo a subunit, on thecontrary, is more difficult to oxidize showing an anodic potential shift of 0.14 V. This indicates a certaininteraction between the two subunits in Dyad, which is additionally confirmed by a slight bathochromicshift of the Q band positions in the UV-vis spectra of Dyad relative to its components. Moreover, thecathodic shift of the second oxidation potential of the ZnPc subunit concerning individual ZnPc reaches0.35 V, indicating an intensification of the electronic interaction between [ZnPc]•+ and Pheo a in Dyad.The spectroelectrochemical experiment showed that the reversible first oxidation of the ZnPc subunit isfollowed by its irreversible second oxidation, which proceeds slightly ahead of the first oxidation of thePheo a fragment. Thus, both electrochemical and spectroelectrochemical studies support the conclusionon the enhanced interaction between [ZnPc]•+ and Pheo a in Dyad, which even leads to a change in theorder of their further oxidations.