π-Extended S-Heterocyclic Naphthoquinodimethane with Dual Diradical and Dipolar Character

The 2,6-naphthoquinodimethane (2,6-NQDM) containing S-heterocyclic molecule 6-S was synthesized, and its dual open-shell diradical and dipolar characters were revealed via both experimental and theoretical studies. Unlike the shorter p-quinodimethane (p-QDM)-containing analogue 5-S, which possesses a closed-shell ground state (y0 = 0%) with small dipolar character, 6-S possesses enhanced dipolar character with a singlet diradical ground state (y0 = 23.3%) and a thermally accessible triplet excited state (ΔEST = -4.13 kcal/mol). Despite this, it displays good stability (t1/2 = 41days) under ambient air and light conditions due to its distinctive dipolar character and kinetic blocking of reactive sites.