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

Abstract

The 2,6-naphthoquinodimethane (2,6-NQDM) containing Sheterocyclic 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 (y 0 = 0%) with small dipolar character, 6-S possesses enhanced dipolar character with a singlet diradical ground state (y 0 = 23.3%) and a thermally accessible triplet excited state (ΔE ST = −4.13 kcal/mol). Despite this, it displays good stability (t 1/2 = 41days) under ambient air and light conditions due to its distinctive dipolar character and kinetic blocking of reactive sites.

Sufficient driving force for quinoidal isoindigo-based diradicaloids with tunable diradical characters

“…The increased aromatic stabilization energy gains for both diradical and zwitterionic forms. 52 The significantly enhanced zwitterionic character also enhances antiaromatic character and then strengthens the diradical character. 53 The effect of attaching different terminal end groups on the relationship between zwitterionic character and diradical character should be clarified in the asymmetric quinoidal isoindigo system, as well as the differences between symmetric and asymmetric systems.…”

Polycyclic aromatic hydrocarbons containing antiaromatic chalcogenopyrano[3,2-b]-chalcogenopyrans

“…1) containing two six-membered rings are antiaromatic and thus extremely unstable. Although several PAHs containing multi-chalcogenopyran rings have been prepared by conjugation extension, [21][22][23][24] compounds with two chalcogenopyran rings fused with each other have been rarely reported due to the unfavorable synthesis and the instability of the products.…”

Zwitterionic Open‐Shell Singlet Diradical with Solvent‐Dependent Singlet–Triplet Energy Gap

“…On the basis of these backgrounds, we focused on zwitterionic diradicals. [13][14][15][16][17][18][19][20][21] We envisaged that zwitterions composed of an electron-donating anion and an electronaccepting cation would resonate with singlet diradical canonical structures and have a small ΔE ST . Their singlet states would have larger dipole moments than their triplet states and would be more stabilized in polar solvents than their triplet states.…”

“…On the basis of these backgrounds, we focused on zwitterionic diradicals [13–21] . We envisaged that zwitterions composed of an electron‐donating anion and an electron‐accepting cation would resonate with singlet diradical canonical structures and have a small Δ E ST .…”