Synthesis of 9-Substituted Fluorene Copolymers via Chemical and Electrochemical Polymer Reaction and Their Optoelectronic Properties

Through Suzuki-Miyaura coupling polymerization and subsequent polymer reactions, we prepared three novel series of poly(fluorene) alternating copolymers consisting of 9-fluorenone (PreP1), 9,9-bis(p-isopropylphenylsulfanyl)fluorene (PI), and 9,9-difluorofluorene (P2) with 9,9-dioctylfluorene. Electrochemical fluorodesulfurization was found to be the key step to convert P1 to P2. This technique provided the selectively and efficiently fluorinated product without undesired side reactions, and could tune the substitution ratio by controlling the quantity of charge passed. The obtained copolymers, PreP1, P1 and P2 were revealed to have the intramolecular charge transfer (ICT) interaction between the electron donor and acceptor moieties, which was supported by DFT calculations. The large stokes shift of P2 (ca.170 nm) observed by optical analyses indicated the large structural difference between its ground-state and excited-state derived from intermolecular excimer formation. Furthermore, the band gap and energy level of the polymers could be tuned by changing the bridged structure at the 9-position of the fluorene unit.