Synthesis and Electrochemical Properties of 2,5-Disubstituted Derivatives of 1,4-Bis(4,5-diphenylidimidazol-2-yl)benzene

Impact of Heterocycle Annulation on NIR Absorbance in Quinoid Thioacene Derivatives

“…Despite the significant interest in benzo-derived quinoids, [10,11] the synthesis and characterisation of the p-methoxyphenyl derivative 4 has only been rudimentary described. [10b] However, 4 is readily synthesed by a Debus-Radziszewski reaction [12a,15] of terephthalaldehyde (10) with p-anisil (11) in 83 % yield, followed by oxidation of the bisimidazole intermediate 12 with ferrous cyanide in 74 % yield. The latter reaction Scheme 2.…”

“…The quinoid 6 was synthesised in two steps from 13 according to the method described by Nakamura (Scheme 2b) [12a] and was adapted for the straightforward synthesis of the corresponding thieno [3,2b]thiophene derivative 7 from 15 (Scheme 2c). The reaction of the bisaldehyde 13 with p-anisil (11) in the presence of ammonium acetate provided 14 in 43 % yield. The formation of the bisimidazole 14 was supported by the new 1 H NMR resonances at δ = 12.79 and 7.92 ppm ([D 6 ]DMSO) for the NH and thiophene CH protons, respectively.…”

“…In contrast to the malononitrile group, the electronic properties of the imidazole moiety can be readily modulated by peripheral substituents [10] in order to achieve the desired electronic state (compare 3 and 4, Scheme 1). [11] Nonetheless, radical properties remain persistent. The introduction of a central heterocycle lead to the stable closed-shell quinoids 5 (X = NMe) and 6 (X = S, Scheme 1) [12] as a result of the reduced aromaticity of the central heterocyclic core.…”