Electrochemistry and spectroelectrochemistry of 5,10,15,20-tetrakis(1,3-benzodioxole) porphyrin and its manganese and iron complexes

Abstract

Cyclic voltammetry and thin-layer spectroelectrochemical properties of the free base 5,10,15,20-tetrakis(1,3-benzodioxole)porphyrin ( H 2 P ), and its manganese and iron complexes ( MnP and FeP , respectively) were studied in dichloromethane with tetra-butyl ammonium hexafluorophosphate (TBAPF6) as supporting electrolyte. The free base undergoes two monoelectronic oxidations at +0.71 and +0.96 V vs. Ag / Ag +, corresponding to the formations of the π-cation radical and dication. Two reductions were observed at -1.53 and -1.87 V corresponding to the formation of π-anion and dianion species. The cyclic voltammograms of the Mn III and Fe III complexes also showed a reversible process centered in the metal ion with E1/2 values at -0.61 and -0.59 V, respectively. In a typical experiment, in situ spectroelectrochemical response showed a decrease of the Soret band at 422 nm, a red shift of the Q-bands, and the new low intensity bands between 800–950 nm range. Structural features and spectroscopic assignments were proposed and discussed based on semi-empirical (molecular mechanics MMFF and ZINDO/S (Zerner method of intermediate neglect of differential overlap for spectroscopy) calculations.