Electroluminescent copolymers based on dihexylfluorene and 2‐{2,6‐bis[2‐(4‐diphenylaminophenyl)vinyl]pyran‐4‐ylidene}malononitrile units

Abstract

AbstractA series of statistical copolymers (poly[(9,9‐di‐n‐hexylfluorene)‐co‐2‐{2,6‐bis‐[2‐(4‐diphenylaminophenyl)vinyl]pyran‐4‐ylidene}malononitrile) were synthesized by the Suzuki coupling reaction. The copolymers showed absorption bands at 379 and 483–489 nm, which were attributed to the oligofluorene segments and the segments containing 2‐[2,6‐bis(2‐{4‐[(4‐bromophenyl)phenylamino]phenyl}vinyl)pyran‐4‐ylidene]malononitrile (3), respectively. The absorption band around 483–489 nm increased with the feed ratio of 3. The photoluminescence (PL) spectra of the copolymers showed emission bands at 420 and 573–620 nm. As the feed ratio of 3 increased, the PL emission in the longer wavelength region redshifted, and the intensity increased as well. The electroluminescence (EL) spectrum of the copolymers showed a very weak emission at 420 nm. The PL and EL emission colors redshifted dramatically with the increase in the feed ratio of 3. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels of the model compound (2‐{2,6‐bis[2‐(4‐diphenylaminophenyl)vinyl]pyran‐4‐ylidene}malononitrile) were determined to be −5.34 and −3.14 eV, respectively. It was concluded that energy transfer took place from the oligofluorene blocks to the segments containing 3 and that direct charge trapping occurred in the segments containing 3 during the EL operation. The Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of the copolymer (x = 0.63, y = 0.37) containing 10 mol % 3 were very close to those (x = 0.67, y = 0.33) for National Television System Committee (NTSC) red with a maximum photometric power efficiency of 0.27 cd/A. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3729–3737, 2006