Blatter Diradicals with a Spin Coupler at the N(1) Position

Abstract

Reactions of a benzo[e][1,2,4]triazine with dilithiobenzenes lead to di-Blatter diradicals connected at the N(1) positions via a spin coupling unit, 1,4-phenylene or 1,3-phenylene. Electrochemical analysis in MeCN revealed four one-electron redox processes separated by 0.1–0.3 V in both diradicals. Variable temperature EPR measurements in polystyrene (PS) solid solutions gave the singlet-triplet energy gaps ΔES-T=2 J of −3.02(11) and −0.16(1) kcal mol−1 for 1,4-phenylene and 1,3-phenylene derivatives, respectively. The latter negative value was attributed to conformational properties of the diradical in the PS solid solution. Results suggest a simple and efficient access to a family of stable Blatter diradicals with a controllable S−T gap through a judicious choice of the arylene coupling unit. DFT calculations indicate that the triplet state is stabilized by (het)arylenes with low LUMO.