Electrochemistry of Nitrated N‐Confused Free‐Base Tetraaryl‐Porphyrins in Nonaqueous Media

Four nitrated N‐confused free‐base tetraarylporphyrins were synthesized and characterized by electrochemistry and spectroelectrochemistry in nonaqueous media. The examined compounds are represented as NO₂(Ar)₄NcpH₂, where NO₂(Ar)₄Ncp is the dianion of a tetraaryl N‐confused porphyrin with an inner carbon bound NO₂ group and Ar is a p‐CH₃OPh, p‐CH₃Ph, Ph or p‐ClPh substituent on each meso‐position of the macrocycle. UV/Vis spectra and NMR spectroscopy data indicate that the same form of the porphyrin exists in CH₂Cl₂ and DMF which is unlike the case of non‐NO₂ N‐confused porphyrins. The Soret band of NO₂(Ar)₄NcpH₂ exhibits a 30–36 nm red‐shift in CH₂Cl₂ and DMF as compared to the spectrum of the non‐NO₂ N‐confused porphyrins. The first two reductions and first oxidation of NO₂(Ar)₄NcpH₂ are reversible in CH₂Cl₂ containing 0.1 M TBAP. The measured HOMO–LUMO gap averages 1.65 V in CH₂Cl₂ and 1.53 V in DMF, with both values being similar to those of the non‐NO₂ substituted compounds. The nitro group on the inverted pyrrole is itself not reduced within the negative potential limit of CH₂Cl₂ or DMF, but its presence significantly affects both the UV/Vis spectra and redox potentials.