Behaviour of Regioisomeric Bithiophenes in the Oxidative Synthesis of Tetrathieno‐Fused π‐Expanded Fluorenes and Their Characterization

• Published in: Asian journal of organic chemistry 2020-12, Vol.9 (12), p.2144-2152
• Main Authors: Jagarapu, Ramakrishna, Maddala, Sudhakar, Mahto, Indrajit, Venkatakrishnan, Parthasarathy
• Format: Article
• Language: English
• Subjects: bithiophene; electrochemical; Electrochemical analysis; fluorene; optical; Optical properties; Organic chemistry; oxidative photocyclization
• ISSN: 2193-5807; 2193-5815
• DOI: 10.1002/ajoc.202000402

Differently‐linked bithienyl‐attached fluorenes have been synthesized. While the oxidative photodicyclization of 2,3′‐bithiophene‐containing fluorene was successful to yield tetrathieno‐fused regioisomeric π‐expanded fluorenes, the reaction with 2,2′‐bithiophene‐containing fluorene was very sluggish. Interestingly, the connectivity in bithiophenes appears to determine the (photo)reactivity. On the one hand, under mild Scholl conditions, 2,3′‐bithiophene‐containing fluorene yielded a highly regioselective product while 2,2′‐bithiophene‐containing fluorene led to polymerization. The optical and electrochemical properties of tetrathienoannulated π‐expanded fluorenes were investigated, and they were found to be quite different from those of the phenanthreno‐annulated π‐expanded analogues. These newly obtained sulfur‐edged π‐expanded fluorenes may hold promise in organic electronics. Connectivity Does Matter: Oxidative (photo)cyclization of differently‐linked‐bithiophene anchored fluorene is found to depend on the connectivity in bithiophene. The optical studies of the oxidatively dicyclized π‐expanded tetrathieno‐annulated fluorenes reveal that they are blue‐emissive. Their electrochemical properties support an air‐stable nature. These characteristics may promote their entry into organic electronics.