Cyclization of Tetraaryl-Substituted Benzoquinones and Hydroquinones through the Scholl Reaction

2,3,5,6-Tetrakis­(5′-dodecylthiophen-2-yl)-benzoquinones and 2,3,5,6-tetrakis­(5′-dodecylthiophen-2′-yl)-hydroquinones were prepared via the Stille or Suzuki cross-coupling reactions, followed by oxidation by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in the case that aryl groups are dodecylthiophenyl. 2,3,5,6-Tetrakis­(5′-dodecylthiophen-2′-yl)­benzoquinone and 2,3,5,6-tetrakis­(5′-dodecylthiophen-2′-yl)-1,4-bis­(dodecyloxy)­benzene underwent the Scholl reaction to give their corresponding predictable cyclization products anthra­[2,1-b:3,4-b′:6,5-b″:7,8-b‴]­tetrathiophene-7,14-dione (3) and anthra­[1,2-b:4,3-b′:5,6-b″:8,7-b‴]­tetrathiophene (5), respectively. Cyclization of 2,3,4,5-tetra­(p-tert-butyl-phenyl) benzoquinones through the Scholl reaction, however, gave rise to a mixture of two cyclization products including an unusual major product, benzo­[4′,5′]­furo­[3′,2′:3,4]­triphenyleno­[1,2-b]­benzofuran (9), with 84% yield and a minor product, 2,3-diphenyltriphenylene-1,4-diol (10), with 11% yield. In contrast, cyclization of 2,3,4,5-tetrakis­(p-dodecyloxyphenyl)­benzoquinone only afforded 2,3-diphenyltriphenylene-1,4-diol (8) with 34% yield. The optical and electrochemistry properties of these fused aromatics were studied. Light emitting diode devices using compound 9 as the fluorescent dopant were fabricated. A maximum external quantum efficiency of 3.23% was achieved for a 4,4′-bis­(carbazole)­biphenyl/9 based device, revealing the potential for such fused aromatics as dopant to be a blue LED component, subject to the functionalization on these novel π-structures as well as further device optimization.