Effect of axial ligands on the spectroelectrochemical properties of zinc phthalocyanine films. In situ Raman and electroreflection spectra

Abstract

Electroreflection and Raman spectra (in situ and ex situ) of zinc phthalocyanine (ZnPc) films (80 nm thick) have been studied. Raman spectra were resonantly and preresonantly enhanced. Both electroreflection and Raman experiments reveal the homogeneous inclusion of electrolyte anions upon oxidation of the film. The anions coordinate preferentially axial positions of the ZnPc molecule. This process is accompanied by an out-of-plane deformation of the phthalocyanine macrocycle, which results in the change of both electroreflection and Raman spectra. The ZnPc molecule remains deformed when the film is saturated with anions. The detailed analysis of new bands and altered intensities in the Raman spectrum indicates that the molecular symmetry point group changes from the D 4 h point group to C 2 v . The influence of ZnPc oxidation on the Raman excitation mechanism has been also studied. Effects of axial ligands on the molecular geometry have been studied by quantum chemical calculations for the ZnPc +, ZnPc +Cl − and ZnPc +(Cl −) 2 species using the unrestricted Hartree—Fock variant of the MNDO method. Calculation results show that the ZnPc molecule undergoes an out-of-plane deformation when one axial position is coordinated by the anion.