Redox Active Quinoidal 1,2,4-Benzotriazines

Modifying the para-quinonimine 1,3-diphenyl-1,2,4-benzotriazin-7­(1H)-one (2a) (E1/2–1/0 −1.20 V), by replacing the N1-phenyl
by pentafluorophenyl, the C3-phenyl by trifluoromethyl, or the C7
carbonyl by ylidenemalononitrile, led to improved electron affinities
as determined by cyclic voltammetry and computational studies. Combining
structural changes further improved electron accepting abilities:
the most electron deficient analogues (E1/2–1/0 ∼ −0.65 V) involved combining
the ylidenemalononitrile groups at C7 with the trifluoromethyl groups
at C3. 1,2,5-Thiadiazolo fusion at C5–C6 did not affect the
redox behavior but did enhance the UV–vis absorption profile.
During the synthesis of the thiadiazolo analogues, 1,4-thiazino-fused
analogues 6 were obtained in low yield, which thermally
ring contract to the triazafluoranthenones 7. Compounds
are fully characterized, and X-ray data are provided for selected
analogues.