A new cyanofluorene-triphenylamine copolymer: Synthesis and photoinduced intramolecular electron transfer processes

A new π-conjugated copolymer, namely, poly{cyanofluore-alt-[5(N, N′-diphenylamino)phenylenevinylene]} ((CNF-TPA)_n), was synthesized by condensation polymerization of 2,2′(9,9-dioctyl-9H- fluorene-2,7-diyl)diacetonitrile and 5-(N,N′-diphenylamino)benzene-1,3- dicarbaldehyde by using the Knoevenagel reaction. By design, diphenylamine, alkylfluorene and poly(p-phenylenevinylene) linkages were combined to form a (CNF-TPA)_n copolymer which exhibits high thermal stability and glass-transition temperature. Photodynamic measurements in polar benzonitrile indicate fast and efficient photoinduced electron transfer (≈10₁₁ s_-1) from triphenylamine (TPA) to cyanofluorene (CNF) to produce the long-lived charge-separated state (90 μs). The finding that the charge-recombination process of (CNF^̇-- TPA_̇+) _n is much slower than the charge separation in polar benzonitrile suggests a potential application in molecular-level electronic and optoelectronic devices.