Optical and electronic properties of fluorene-based copolymers and their sensory applications

A series of novel, fluorene-based conjugated copolymers, poly[(9,9-bis{propenyl}-9H-fluorene)-co-(9,9-dihexyl9H-fluorene)] (P1), poly[(9,9-bis{carboxymethylsulfonyl-propyl}- fluorenyl-2,7-diyl)-co-(9,9-dihexyl-9H-fluorene)] (P2) and poly[(9,9- dihexylfluorene)-co-alt-(9,9-bis-(6-azidohexyl)fluorene)] (P3), are synthesized by Suzuki coupling reactions and their electrochemical properties, in the form of films, are investigated using cyclic voltammetry. The results reveal that the polymer films exhibit electrochromic properties with a pseudo-reversible redox behavior; transparent in the neutral state and dark violet in the oxidized state. Among the three polymers, P2 possesses the shortest response time and the highest coloration efficiency value. These polymers emit blue light with a band gap value of around 2.9 eV and have high fluorescent quantum yields. Their metal ion sensory abilities are also investigated by titrating them with a number of different transition metal ions; all of these polymers exhibit a higher selectivity toward Fe3þ ions than the other ions tested with Stern–Volmer constants of 4.41 106 M1 , 3.28 107 M1 , 1.25 106 M1 , and 6.56 106 M1 for P1, P2, water soluble version of P2 (P2S) and P3, respectively.