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.