Synthesis, characterization, and electroluminescence of polyfluorene copolymers containing T-shaped isophorone derivatives

Abstract

We have successfully synthesized a series of new fluorene-based copolymers, poly[(9,9-bis(4-octyloxy-phenyl)fluorene-2,7-diyl)-co-[2(3{2[4(2{4[bis(bromophenyl-4yl) amino]phenyl}vinyl)-2,5-bisoctyloxyphenyl]vinyl}-5,5-dimethyl-cyclohex-2-enylidene)malononitrile] (PFTBMs), with varying molar ratios of the low-energy band gap comonomer, 2(3{2[4(2{4[bis(4-bromophenyl)amino]phenyl}vinyl)-2,5-bisoctyloxyphenyl]vinyl}-5,5-dimethyl-cyclohex-2-enylidene)malononitrile (BTBM). To prepare BTBM (which has a T-shaped structure) from triphenylamine, dialkoxy phenyl, and isophorone, we introduced three individual segments of an isophorone derivative containing two cyanide groups at the carbonyl position, a dialkoxy phenyl group for increased solubility, and a triphenyl amine for effective charge transfer. Furthermore, we introduced vinyl linkages between each segment to increase the length of π-conjugation. The synthesized polyfluorene copolymers with the BTBM, PFTBMs, were synthesized via palladium-catalyzed Suzuki coupling reactions. The photoluminescence emission spectra of the synthesized polymers in solution did not show significant energy transfer from PBOPF segments to the BTBM units. Light-emitting devices based on these polymers were fabricated with an indium tin oxide/poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/polymers/Balq/LiF/Al configuration. Examination of the electroluminescence emission of the synthesized polymers showed that the maximum wavelength shifted continuously toward long wavelengths with as the number of BTBM units in the polymer main chain was increased. In particular, a device using PFTBM 05 exhibited a maximum brightness of 510 cd/m2 and a maximum current efficiency of 0.57 cd/A. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 82–90, 2010