Air‐Stable Radical Ion Pairs Formed from 20π‐Electron 5,15‐Diazaporphyrinoids and Tetracyanoquinodimethane Derivatives

Abstract With the aim of exploring 5,15‐diazaporphyrinoids with four meso substituents (R 4 DAP) as a new class of π‐electron donors, the generation of air‐stable π‐radical ion pairs formed from R 4 DAP and 7,7,8,8‐tetracyanoquinodimethane (TCNQ) derivatives has been demonstrated. Nickel(II) and copper(II) complexes of the 20π‐electron antiaromatic R 4 DAP (R 4 DAPM; M = Ni, Cu) were prepared via a metal‐templated cyclization method and used for the reaction with TCNQ. Single electron transfer from R 4 DAPM to TCNQ spontaneously occurred in CH 2 Cl 2 at room temperature to afford the corresponding radical ion pair, [R 4 DAPM •+ ][TCNQ •− ]. Similarly, R 4 DAPNi reacted with 2,3,5,6‐tetrafluoro‐TCNQ (F 4 TCNQ) to afford [R 4 DAPNi •+ ][F 4 TCNQ •− ]. The absorption spectra of [R 4 DAPM •+ ][TCNQ •− ] in the visible–near IR region were almost identical to the superposed spectra of the independently prepared cation‐ and anion‐radical references, indicating negligible π─π orbital interaction between the two radical ions in solution. However, the electron paramagnetic resonance spectrum of [R 4 DAPNi •+ ][F 4 TCNQ •− ] in CH 2 Cl 2 showed a broad signal attributable to the coupled spin state, suggesting the definite contribution of spin–spin interaction between the two ion‐paired radicals. The results of this study provide valuable information for understanding the fundamental properties of π‐radical ion pairs.