Electrochemical and Spectral Properties of Highly Distorted Rhenium Phthalocyanine Complexes

Abstract

Phthalocyanines exhibit distinct physicochemical properties by modifying the π-conjugated system which makes them as the suitable candidates for various applications. Recently, we synthesized and characterized rhenium phthalocyanine (Re1Pc, Re2Pc) and rhenium tetraazaporphyrin (Re1TAP, Re2TAP) complexes (Figure 1 (a)).1 In terms of electrochemical properties (Figure 1 (c)), compared to the corresponding Zn complexes (ZnPc, ZnTAP), both the first oxidation and the first reduction potentials of Re complexes (Re1Pc, Re2Pc, Re1TAP, Re2TAP) shift to the positive side owing to the introduction of electron-deficient [Re(CO)3]+ unit(s). On the other hand, by reducing the π-conjugated system from Pc to TAP, more positive oxidation potentials are observed in the ReTAP complexes. This trend is consistent with the changes in the calculated HOMO and LUMO energy levels (Figure 1 (b)). Notably, the positively shifted oxidation potentials of these complexes significantly improve the tolerance towards oxidation, which is essential for various applications.In the electronic absorption spectra of these Re complexes, the unsymmetric coordination of the [Re(CO)3]+ unit(s) concomitantly produces a remarkable red shift of the Q band. Also, in ReTAP complexes, the broadening of the Q bands is uniquely observed.DFT calculations indicate that the macrocycle skeletons in Pc and TAP are highly distorted, in contrast to the high stability towards oxidation. In the presentation, the distorted structures will be discussed in detail.[1] K. Murata, Y. Koike, K. Ishii, Chem. Commun., 2020, 56, 13760-13763.Figure 1. (a) Molecular structures of RePc and ReTAP complexes. (b) Energy plots of the molecular orbitals and (c) the electrochemical results of MPc and MTAP complexes. Figure 1