High-Spin Diradical Dication of Chiral π-Conjugated Double Helical Molecule

• DOI: 10.1021/jacs.9b08711
• Publication Date: 2019-10-09T14:29:00Z
• Authors: Chan Shu; Hui Zhang; Arnon Olankitwanit; Suchada Rajca; Andrzej Rajca
• Keywords: Diradical; Dication; Helicene; Radical ion

We report an air-stable diradical dication of chiral D2-symmetric conjoined bis[5]diazahelicene with unprecedented high-spin (triplet) ground state, singlet triplet energy gap, ΔEST = 0.3 kcal mol–1. The possesses closed-shell (Kekulé) resonance forms 16 π-electron perimeters. is monomeric in dibutyl phthalate (DBP) matrix at low temperatures, and it has a half-life more than 2 weeks ambient conditions the presence excess oxidant. A barrier ∼35 mol–1 been experimentally determined for inversion configuration neutral bis[5]diazahelicene, while barriers its radical cation were predicted by DFT computations to be within few that species. Chiral HPLC resolution provides enriched (P,P)- or (M,M)-enantiomers. enantiomerically configurationally stable 48 h room temperature, thus providing lower limit 27 enantiomers show strong chirooptical properties are comparable [6]helicene carbon–sulfur [7]helicene, as anisotropy factors, |g| |Δε|/ε 0.007 348 nm (neutral) 0.005 385 (diradical dication). suggest SOMO HOMO levels near-degenerate.