Cyclobis(7,8‐(para‐quinodimethane)‐4,4′‐triphenylamine) and Its Cationic Species Showing Annulene‐Like Global (Anti)Aromaticity

Abstract

p-Conjugated macrocycles containing all-benzenoid rings usually show local aromaticity,but reported herein is the macrocycle CBQT,c ontaining alternating para-quinodimethane and triphenylamine units displaying annulene-like antiaromaticity at low temperatures as aresult of structural rigidity and participation of the bridging nitrogen atoms in pconjugation. It was easily synthesized by intermolecular Friedel-Crafts alkylation followed by oxidative dehydrogenation. X-rayc rystallographic structures of CBQT,a sw ell as those of its dication, trication, and tetracation were obtained. The dication and tetracation exhibited global aromaticity and antiaromaticity,r espectively,a sconfirmed by NMR measurements and theoretical calculations.B oth the dication and tetracation possess open-shell singlet ground states,w ith as mall singlet-triplet gap.

Dark State of the Thiele Hydrocarbon: Efficient Solvatochromic Emission from a Nonpolar Centrosymmetric Singlet Diradicaloid

“…TTH shows four reversible redox couples related to the formation of the radical–anion ( E 1/2 = −1.047 V vs Fc/Fc + ), anion–anion ( E 1/2 = −1.572 V vs Fc/Fc + ), radical–cation ( E 1/2 = +1.030 V vs Fc/Fc + ), and cation–cation ( E 1/2 = +1.278 V vs Fc/Fc + ) species (Figure a). This result is impressive, considering the small dimensions of the p QDM derivative. − The quinoidal stabilization of the diradicaloid determines a slightly reduced electron-acceptor character compared to both TTM and PTH . , The electrochemical band gap (Figure b) of 2.08 eV resulted to be 0.1 eV smaller than the optical one. The amphoteric redox behavior of TTH with four reversible redox couples makes this diradicaloid a promising candidate for energy storage applications , or air-stable organic field-effect transistors (OFETs), , especially considering the ambipolar behavior that is usually displayed by singlet diradicaloids …”