1,3-Diphenyl-7-trifluoromethyl-1,4-dihydro-1,2,4-benzotriazin-4-yl (4), prepared in high yield via the catalytic oxidation of the corresponding amidrazone 5 by using Pd/C (1.6 mol %) and 1,8-diazabicyclo[5.4.0]undec-7-ene (0.1 equiv) in air, is stable in dichloromethane solutions in the presence of MnO(2) and KMnO(4). Furthermore, radical 4 is thermally stable well past its melting point (160-161 °C) with a decomposition onset temperature of 288 °C. X-ray studies show that radical 4 packs in equidistant slipped π-stacks along the a axis. Cyclic voltammetry shows two fully reversible waves, corresponding to the -1/0, 0/+1 processes. EPR studies indicate that the spin density is mainly delocalized on the triazinyl fragment of the heterocycle. Magnetic susceptibility measurements in the 5-300 K region showed that the radical obeys Curie-Weiss behavior down to 10 K (C = 0.376 emu·K·mol(-1) and θ = +1.41 K) consistent with weak ferromagnetic interactions between S = 1/2 radicals. Subsequent fitting of the magnetic data to a 1D ferromagnetic chain model provided an excellent fit (g = 2.00, J/k = +1.49 K) down to 10 K but failed to reproduce the subsequent decrease in χT at lower temperatures, which has been ascribed to the onset of weaker antiferromagnetic interactions between ferromagnetic chains.

1,3-Diphenylbenzo[e][1,2,4]triazin-7(1H)-one (6) reacts with tetracyanoethylene (TCNE) or tetracyanoethylene oxide (TCNEO) to give the deep green 2-[1,3-diphenylbenzo[e][1,2,4]triazin-7(1H)-ylidene]propanedinitrile (11) in 17 and 15% yields, respectively. Nucleophiles such as amines, alkoxides, thiols and Grignard reagents all reacted with the 1,3-diphenylbenzotriazinone 6 regioselectively at C-6, while halogenating agents reacted exclusively at C-8. Furthermore, 8-iodo-1,3-diphenylbenzo[e][1,2,4]triazin-7(1H)-one (32) undergoes palladium-catalysed Suzuki-Miyaura and Stille coupling reactions to give 8-aryl- or heteroaryl-substituted benzotriazinones. By combining both the C-6 and C-8 chemistries 1,3,6,8-tetraphenylbenzo[e][1,2,4]triazin-7(1H)-one (42) and 1,3-diphenyl-6,8-di(thien-2-yl)-benzo[e][1,2,4]triazin-7(1H)-one (43) can be prepared. All new compounds are fully characterized.

Regioselective nucleophilic addition of bisnucleophiles 1,2-benzenediamine, 2-amino-benzenethiol, and N-phenyl-1,2-benzenediamine to 1,3-diphenylbenzo[e][1,2,4]triazin-7(1H)-one (1) at C6 followed by intramolecular cyclocondensation at the C7 carbonyl afforded highly coloured tetracenes 1,3-diphenyl-1,6-dihydro-[1,2,4]triazino[5,6-b]phenazin-4-ium 4-methylbenzenesulfonate (12), 1,3-diphenyl-1H-[1,2,4]triazino[6,5-b]phenothiazine (14) and 1,3,11-triphenyl-1,6-dihydro-[1,2,4]triazino[5,6-b]phenazin-11-ium 4-methylbenzenesulfonate (15), respectively. Neutralization of the latter with alkali gave the free base 1,3,11-triphenyl-1H-[1,2,4]triazino[5,6-b]phenazin-11-ium-6-ide (16). Furthermore, the benzotriazinone 1 reacts with dimethyl malonate to give 6-(methoxycarbonyl)-7-oxo-1,3-diphenyl-7H-benzofuro[5,6-e][1,2,4]triazin-1-ium-4-ide (17) in 74% yield, while with S(4)N(4) [5,6-c]-thiadiazolo-7-oxo-1,3-diphenyl-1,2,4-benzotriazine (22) was formed in 15% yield. The free bases 16 and 17 display negative solvatochromism, which supports charge separated ground states similar to those of zwitterionic biscyanines, and DFT calculations at the UB3LYP/6-31G(d) level afford ΔE(ST) values of -13.6 and -18.7 kcal mol(-1), respectively that strongly favour the singlet ground state. All ring systems described are new and fully characterized.

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