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

A new pi-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 ( approximately 10(11) s(-1)) from triphenylamine (TPA) to cyanofluorene (CNF) to produce the long-lived charge-separated state (90 mus). 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.