Design, synthesis, photophysical, and electrochemical properties of DCM-based conjugated polymers for light-emitting devices

Abstract

A series of conjugated hyperbranched polymers, hyperbranched copolymers, and linear polymers containing 2-pyran-4-ylidenemalononitrile (acceptor) and triphenylamine/fluorene (donor) units were synthesized and characterized by FTIR, 1H NMR, thermogravimetric analyses, differential scanning calorimetry, gel permeation chromatography, UVvisible, photoluminescence, and cyclic voltammetry measurements. All the polymers show red-light emission in the range of 566656 nm both in solution and in solid state. The quantum efficiency of the polymers was in the range of 5682%. Among the six polymers synthesized, only polymers containing fluorene units show Tg and polymers based on triphenylamine not exhibit Tg. The band gap of these polymers were found to be reasonably low; hyperbranched copolymer containing fluorene unit shows lowest band gap of 2.18 eV due to the stabilization of LUMO energy level by the electron withdrawing ?CN groups. The thermal and solubility behavior of the polymers were found to be good. All the EL spectra of the devices (indium-tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/polymer/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline/tris(8-hydroxyquinoline)aluminum)/LiF/Al) show red-light emission, and the device fabricated with P3 and P4 shows maximum luminance and luminous efficiency of 4104 cd m-2 and 0.55 cd angstrom-1 and 3696 cd m-2 and 0.47 cd angstrom-1, respectively, indicates that they had the best carrier balance. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012