1,3-Diradicals Embedded in Curved Paraphenylene Units: Singlet versus Triplet State and In-Plane Aromaticity

Curved π-conjugated molecules and open-shell structures have attracted much attention from the perspective of fundamental chemistry, as well materials science. In this study, chemistry 1,3-diradicals (DRs) embedded in curved cycloparaphenylene (CPPs) structures, DR-(n+3)CPPs (n = 0–5), was investigated to understand effects curvature system size on spin–spin interactions singlet versus triplet state, their unique characteristics such in-plane aromaticity. A ground state predicted for larger 1,3-diradicals, seven- eight-paraphenylene-unit-containing diradicals DR-7CPP 4) DR-8CPP 5), by quantum chemical calculations. The smaller-sized 0–3) were found possess states. Thus, ground-state spin multiplicity is controlled paraphenylene cycle. effect confirmed experimental generation DR-6CPP photochemical denitrogenation its azo-containing precursor (AZ-6CPP). Intriguingly, a type aromaticity emerged states S-DR-4CPP 1), proven nucleus-independent shift calculations (NICS) an analysis anisotropy induced current density (ACID), which demonstrate that homoconjugation between 1,3-diradical moiety arises because distorted bonding system.