Abstract
Abstract Unlike the light-emitting polymers published in the literatures, the aim of this research utilize the new monomer- 3,4-diphenylmaleimide derivative as the main monomer, to develop a series of novel light-emitting polymers. The contents of the thesis can be divided into two parts, one is to synthesize semi-conjugated light-emitting polymers, and the other is to synthesize fully-conjugated light-emitting polymers. Most of known red light-emitting polymers are not easily accessible and require lengthy synthesis procedure in the preparation of suitable monomers. In the first part of the study, we report readily method to synthesize a series of 3,4-diphenylmaleimide-based copolymers. The maleimide-based red-fluorescent polymers were easily synthesized from palladium catalyzed polycondensation of N-alkyl-3,4-bis (4-bromophenyl)maleimide with commercially available or readily prepared primary arylamines or secondary aryldiamines. The resulting polymers derived from primary arylamines in general show low molecular weight. The low molecular weight of the primary arylamine-derived polymer can be attributed to the unfavored close proximity of the adjacent maleimide rings. Compared the fluorescence spectra in a solution with in a solid film, these copolymers suffered from serious problem of self-aggregation. With judiciously selection of arylamine monomers, the self-aggregation and red-shifting of the solid film fluorescence can be largely diminished. A PLED was fabricated for preliminary test of the red electroluminescence (EL), it showed EL corresponding to CIEx,y of (0.66, 0.33), which is comparable with or better than CIEx,y of (0.64, 0.33), the standard red color of National Television System Committee (NTSC). To enhance the device efficiency and the degree of polymerization of polymers, a series of newly designed 3,4-diphenylmaleimide-based □-conjugated copolymers were synthesized in the second part of study. In addition, to investigate the light-emitting behaviors of copolymers, we also designed five model compounds to study. Compared the 3,4-diphenylmaleimide derivative used in the first part of study, we use ethylhexyl group instead of methyl group on the N-position of maleimide. It found that the substitutent of maleimide play an important role in preventing of molecules self-aggregation. Polymer light-emitting diodes (PLEDs) fabricated from PTTML exhibited saturated red electroluminescence (EL) corresponding to CIEx,y of (0.66, 0.33) with emission □maxEL of 676 nm. TPBI (2,2’,2’’-(1,3,5-phenylene)-tris-(1-phenyl-1H-benzimidazole), as the electron-transporting layer in PLEDs was found to improve the performance of 3,4-diphenylmaleimide-bithiophene copolymer (PBTML). PBTML PLED yielded reddish EL (emission □maxEL of 620 nm) with peak efficiencies of 0.89 cd/A and a maximum electroluminance of 1290 cd/m2. PFTML PLEDs yielded bright orange-red EL (emission □maxEL of 614 nm) with a high intensity of over 2000 cd/m2 and an enhanced peak luminous efficiency of 1.25 cd/A, or an external quantum efficiency of 0.74%. PFBTML PLED yielded reddish EL (corresponding to CIEx,y of (0.60, 0.40) with emission □maxEL of 624nm) with peak efficiencies of 1.03 cd/A and a maximum electroluminance of 1230 cd/m2.