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 NO 2 (Ar) 4 NcpH 2 , where NO 2 (Ar) 4 Ncp is the dianion of a tetraaryl N‐confused porphyrin with an inner carbon bound NO 2 group and Ar is a p ‐CH 3 OPh, p ‐CH 3 Ph, 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 CH 2 Cl 2 and DMF which is unlike the case of non‐NO 2 N‐confused porphyrins. The Soret band of NO 2 (Ar) 4 NcpH 2 exhibits a 30–36 nm red‐shift in CH 2 Cl 2 and DMF as compared to the spectrum of the non‐NO 2 N‐confused porphyrins. The first two reductions and first oxidation of NO 2 (Ar) 4 NcpH 2 are reversible in CH 2 Cl 2 containing 0.1  M TBAP. The measured HOMO–LUMO gap averages 1.65 V in CH 2 Cl 2 and 1.53 V in DMF, with both values being similar to those of the non‐NO 2 substituted compounds. The nitro group on the inverted pyrrole is itself not reduced within the negative potential limit of CH 2 Cl 2 or DMF, but its presence significantly affects both the UV/Vis spectra and redox potentials.