Meso‐tetrakis[2.2]paracyclophanylporphyrin: Electronic structure and electrochemical behavior

Abstract

AbstractReplacement of all phenyl groups in meso‐tetraphenylporphyrin, TPP, by [2.2]paracyclophane, PCP, enhances the increase of energy of the HOMO and HOMO‐1 of porphine, P, already noticed for the mono‐[2.2]paracyclophanyl‐substituted TPP, and fills the energy gap by the occupied MOs of the PCP units. The first oxidation half‐wave potential is respectively decreased to 0.52 V. The CNDO/S‐CIS calculations agree with the experimental bathochromic shifts of all bands in the electronic spectra of the considered atropoisomers of the title compound, TPCPP, as compared to TPP. In the excited B states the interactions between the PCP and porphine units are represented mainly by the charge transfer of 0.44 e from PCP to P, according to transition density matrix calculations. While electroreduction of the title compound results in a successive formation of the anion radical and dianion, oxidation represents a four‐step process involving one electron transfer per step, and resulting in the oxidation of two PCP units. Formation of the conductive polymeric film on the electrode seems to be connected with the transient formation of a quinoid system of bonds.