it-Stacked Ion Pairs: Tightly Associated Charged Porphyrins in Ordered Arrangement Enabling Radical-Pair Formation

pi-Electronic ion pairs are of interest for fabricating electronic materials that use intermolecular interactions based on electrostatic and dispersion forces, defined as i pi-i pi interactions, to provide dimension-controlled assemblies. Porphyrin ions, whose charge is delocalized in the core units, are suitable for ordered arrangement and assemblies by ion pairing. Herein, charged porphyrins were found to form solid-state assemblies and solution-state stacked ion pairs according to the peripheral electron-donating groups (EDGs) and electron-withdrawing groups (EWGs). The concentration-dependent 1H NMR signal shifts of a porphyrin ion pair, comprising a meso-EWG cation and a meso- EWG anion, provided a hetero-dimerization constant of 2.8 x 105 M-1 in CD2Cl2 at 20 degrees C. In the ion pair of a meso-EWG cation and a meso-EDG anion, the electron transfer in the steady and excited states according to solvent polarity and photoexcitation, respectively, produced the radical pairs. The electron spin resonance analysis in frozen toluene revealed the formation of a heterodiradical in a closely stacked structure by the antiferromagnetic dipolar interaction and temperature-dependent spin transfer behavior.

Automated summary

Charged porphyrins can form solid-state assemblies and solution-state stacked ion pairs based on peripheral electron-donating and electron-withdrawing groups. Concentration-dependent 1H NMR signal shifts and electron spin resonance analysis revealed antiferromagnetic dipolar interactions and temperature-dependent spin transfer behavior in this process.