Synthesis and characterization of fluorene tethered benzo[c]thiophene/benzo[c]- selenophene analogs Natarajan Senthil Kumar, Arasambattu K. Mohanakrishnan * Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai 600 025, Tamil Nadu, India article info Article history: Received 9 April 2010 Received in revised form 13 May 2010 Accepted 15 May 2010 Available online 11 June 2010 Keywords: Disubstituted fluorene Benzo[c]thiophene Lawesson’s reagent Woollins reagent Cyclic Voltamogram Band gap abstract Synthesis of 9,9-dialkyl/diarylfluorene based benzo[c]thiophene/benzo[c]selenophenes is presented. The synthesis of benzo[c]thiophene analogs is also realized with fluorene containing one or two thiophene units. The optical and electrochemical studies of fluorenyl benzo[c]heterocycles are correlated with their structures. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Conjugated thienyl oligomers attract much attention by their unique optical and semiconducting properties. 1 They can be used as Organic Light Emitting Diodes (OLEDs) 2 and Organic Field Effect Transistors (OFETs). 3 Oligomers can be easily tuned to the desired properties by changing the structure, by inserting various func- tional groups like 2-n-hexylfluorene, 9,9-diphenyl fluorene, 4 and oligothiophene/functionalized truxene. 5 Polythiophene and its derivatives are often used as optoelectonic materials because of their high electrical conductivity and thermal stability in both neutral and doped states. 6 The fluorene incorporated poly- thiophene materials exhibit relatively high photo and electrolu- minescence quantum efficiency than polythiophene materials. 7 Perepichka and co-workers synthesized poly star shaped tris- EDOT coupled terthienobenzene, which showed switching be- tween red- and blue-colored stable states. 8 Now a days plenty of fluorene incorporated materials have been synthesized and used in electronic application especially ortho-linked spirobifluorene have unique photophysical properties and high triplet energy because of the p-conjugation interruption between spirobifluorene units. 9 Bao and co-workers reported the synthesis of fluorene coupled oligo- thiophenes as high performance semiconductors for organic thin film transistors. 10 Huang and co-workers outlined the synthesis of 2,7-dipyrenyl-9-phenyl-9-pyrenyl fluorene moiety as blue emitters in nondoped OLEDs without the need for hole-injection layers for simplifying device fabrication. 11 Ding and co-workers reported the synthesis of copolymers of fluorene and oxadiazole as Polymer Light Emitting Diodes (PLEDs). 12 Lee and co-workers outlined the synthesis of oligo(9,9- dihexyl-2,7-fluoreneethynylene)s as blue light emitting diodes. 13 Beifield and Yao reported the synthesis of two-photon absorbing unsymmetrical branched chromophores containing fluorene moi- ety. 14 Recently, Yang and co-workers synthesized novel oligo-9,9 0 - spirobifluorenes through ortho-linkage as full hydrocarbon phos- phorescent OLEDs. 15 Wong and co-workers reported the synthesis of novel (9,9-di-p-tolylfluorene) analogs containing thiophene and pyridine rings. 16 Rodriguez and co-workers reported the synthesis and optical characterization of thiophene and fluorene derivatives containing ethynyl spacers. 17 Promarak and co-workers reported the synthesis of conjugated fluorenyl oligothiophenes and showed the decrease in oxidation potential and increase in absorption maxima with in- creasing the number of thiophene rings on fluorene moiety. 18 They have also synthesized N-carbazole end-capped oligothiophene- fluorenes as potential hole-transporting and light-emitting layers in OLED devices. 19 Indenofluorenes are known to have good fluo- rescence properties and have also been investigated for their OLED applications. 20 Recently, linear and star shaped rigid conjugated fluorene and truxene molecules containing terpyridine units are * Corresponding author. Tel.: þ91 44 22202813; fax: þ91 44 22300488; e-mail address: mohan_67@hotmail.com (A.K. Mohanakrishnan). Contents lists available at ScienceDirect Tetrahedron journal homepage: www.elsevier.com/locate/tet 0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2010.05.060 Tetrahedron 66 (2010) 5660e5670