Synthesis of novel heteroquaterphenoquinones and their electrochemical, structural, and spectroscopic characterization

Novel heteroquaterphenoquinones, 5,5'-bis(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-5,5'-dihydro-2,2'-bithienyl (3) and its 2,2'-biselenienyl (4), 2,2'-bifuryl (5), and 2,2'-bi-N-methylpyrrolyl (6) analogues, were synthesized by a stepwise cross-coupling reaction or by a more convenient one-pot oxidative homocoupling reaction of heterocycle-substituted phenols. Despite a highly conjugation-extended system, the quinones 3-6 are very stable in the solid state and in solution in common organic solvents. These quinones undergo a reversible one-stage, two-electron reduction up to dianions and a two-stage, one-electron oxidation reaction up to dications. The E(1)(rcd) of these quinones increases with the increase in the aromaticity of the incorporated heterocycles. The E(1)(ox) of these quinones appears to be specified by the ionization potential of the incorporated heterocycles. Thus, the N-methylquinone 6 exhibiting the lowest E(1)(ox) value exhibits the smallest E(1)(sum) among the quinones 3-6. The quinone 5 was revealed to exist in an unusual O-cis conformation in the solid state by X-ray crystallography, whereas the quinone 3 exists in an S-trans conformation in the solid state. The cis and trans isomers are interconvertible in solution in 3-5, whereas only N-trans isomer was detected for 6 in H-1 NMR spectroscopy. The quinones 3-6 exhibit a very intense absorption maximum in the near-infrared region of 662-827 nm. Of these, the maximum absorption wave length of 6 shifts to a more bathochromic region by 149-165 nm than those of 3-5. The quinones 3-6 can be used as dyestuffs in various fields for laser-driven high-density optical storage media.