Generation and Characterization of a Tetraradical Embedded in a Curved Cyclic Paraphenylene Unit

Abstract

AbstractUnique spin–spin (magnetic) interactions, ring‐size effects on ground‐state spin multiplicity, and in‐plane aromaticity has been found in localized 1,3‐diradicals embedded in curved benzene structures such as cycloparaphenylene (CPP). In this study, we characterized the magnetic interactions in a tetraradical consisting of two localized 1,3‐diradical units connected byp‐quaterphenyl within a curved CPP skeleton by electron paramagnetic resonance (EPR) spectroscopy and quantum chemical calculations. Persistent triplet species with zero‐field splitting parameters similar to those of a triplet 1,3‐diphenylcyclopentane‐1,3‐diyl diradical were observed by continuous wave (CW) or pulsed X‐band EPR measurements. The quintet state derived from the ferromagnetic interaction between the two triplet diradical moieties was not detected at 20 K under glassy matrix conditions. At the B3LYP/6‐31G(d) level of theory, the singlet state was lower in energy than the triplet and quintet states. These findings will aid in the development of open‐shell species for material science application.