pubs.acs.org/Macromolecules Published on Web 03/30/2010 r 2010 American Chemical Society Macromolecules 2010, 43, 3613–3623 3613 DOI: 10.1021/ma100195m Synthesis and Characterization of a New Series of Blue Fluorescent 2,6-Linked 9,10-Diphenylanthrylenephenylene Copolymers and Their Application for Polymer Light-Emitting Diodes Hung-Yang Chen, †,‡,§ Chin-Ti Chen,* ,† and Chao-Tsen Chen* ,§ † Institute of Chemistry, Academia Sinica, Taipei, Taiwan 11529, ‡ Nano Science and Technology Program, TIGP, Academia Sinica, Taipei, Taiwan 11529, and § Department of Chemistry, National Taiwan University, Taipei, Taiwan 10617 Received January 26, 2010; Revised Manuscript Received March 18, 2010 ABSTRACT: A series of new 9,10-diphenylanthracene-based, 2,6-linked blue-light-emitting copolymers bearing hole- or electron-transporter as well as bulky substituent were successfully synthesized. Photo- physical, thermal, electrochemical, and electroluminescence (EL) properties of these copolymers were studied and characterized. Bright and efficient blue fluorescence in the solid state was achieved by incorporating bulky substituent into the copolymer backbone. Both hole- and electron-transport-substituted copolymers apparently enhanced the electroluminescent performance of their polymeric light-emitting diodes (PLEDs). A diphenylvinyl-bearing copolymer (pDPV) PLED exhibited sky-blue EL (λ max EL =473 nm, CIE x,y =0.16, 0.28) with peak luminous efficiency of 2.21 cd/A; a N-carbazole bearing copolymer (pCBZ) PLED displayed a blue EL (λ max EL =469 nm, CIE x,y =0.15, 0.22) with peak luminous efficiency of 2.15 cd/A. OXD-7 (1,3-bis(2-(4-tert- butylphenyl)-1,3,4-oxadiazol-5-yl)benzene) as an electron-transporting dopant was found to improve the performance of PLED significantly. A better balanced hole/electron charge carrier was ascribed to electron- transporting, 1,3,4-oxadiazole-bearing copolymer (pOXD) PLED. It showed a very mild efficiency rolls off: only 0.13 cd/A luminous efficiency drops from current densities of 10-100 mA/cm 2 , corresponding to EL brightness of 169-1558 cd/m 2 . Introduction Blue-light-emitting polymers have been extensively studied due to practical applications of full-color flat-panel displays or renovated solid-state lightings (SSLs). 1 They can serve as the light-emitting layer or the host material for luminous dopants in generating other long-wavelength colors in polymer light- emitting diodes (PLEDs). Blue color fluorophores commonly consist of chemical structures like phenyl, carbazole, fluorene, or heterocyclic rings, such as thiophene, pyridine, and furan. 1 Over the past two decades, a variety of the wide-band-gap polymers with blue-light emission have been developed, they are poly(p-phenylene), poly(dibenzosilole), 2 polyfluorenes, poly- pyridines, and polycarbazoles, etc. For blue fluorophores, ant- hracene is the first reported organic material observed for electroluminescence (EL) in 1963 by Pope and co-workers. 3 Since then, many anthracene derivatives have been developed and applied for organic light-emitting diodes (OLEDs) because of their pure blue fluorescence and high solution fluorescence quantum yields (Φ fs ). Among them, 9,10-substituted anthra- cene derivative has been one of practical chemical structures for blue-emitters 4 or host materials for downhill energy transfer to green- or red-emitters. 5 In the molecular design of these materi- als for OLEDs, electron/hole transporting 4a,d,e as well as bulky π-conjugated moieties 4b,c are often incorporated into the anthracene derivatives. Many of them exhibit excellent efficien- cies. However, for PLEDs, few anthracene-based polymeric materials have shown satisfactory EL efficiency so far. 6-9 The anthracene unit can be incorporated into the polymer chain through several methods, such as the side-chain groups of the polymer. 7 There are many more cases having an extension of the polymer chain through 9,10-linked anthrylene, 6 but very few along 2,6- positions of anthracene derivatives. 8 In spite of high solution fluorescence quantum yields (Φ f ), when fabricated into PLEDs, none of these anthracene-derived blue light-emitting polymers exhibited luminous efficiency more than 1 cd/A, and the electro- luminance of these polymers rarely exceeded 1000 cd/m 2 . More- over, either 9,10- or 2,6-linked anthrylene polymers often show red-shifting EL having downgrade blue color purity. Therefore, the development of efficient and bright anthracene-derived blue light-emitting polymers for PLEDs applications still remains a challenge. In this work, we report a series of new 9,10-diphenylanthracene (DPA)-derived blue fluorescent copolymers. Since the extension of the copolymer chain is through the 2,6-positions of DPA, these copolymers enable the chemical grafting with hole-transporting, electron-transporting, or bulky π-conjugation moiety on DPA unit. In order to preserve the intrinsic wide-band-gap energy of DPA for blue EL, we adopt a dioctyl-substituted phenylene unit as the comonomer for the copolymerization with 2,6-linked anthrylene derivatives. Such phenylene unit plays a role of the π-conjugation twister between each 2,6-linked anthrylene unit in the polymer backbone. The synthesis, characterization, and EL properties of these novel blue light-emitting copolymers are reported herein. Influences of the substituted group, including hole injection/transport, electron injection/transport, and bulky moieties, on the EL performance of these blue light-emitting copolymers are also discussed. To the best of our knowledge, the EL performance of 2,6-linked anthrylenephenylene copolymers reported here is one of the best among all anthracene-derived PLEDs reported so far. Our results also provide insightful *Corresponding authors. E-mail: cchen@chem.sinica.edu.tw, chenct@ ntu.edu.tw.