Synthesis of New Fluorene-Indolocarbazole Alternating Copolymers for Light-Emitting Diodes and Field Effect Transistors

Abstract

New alternating copolymers of poly (2,7-(9,9 0 -dihexylfluorene)-alt-3,9-(5,11-di(2-ethylhexyl)-indolo[3,2-b]carbazole)) (PFp-In) and poly (2,7-(9,9 0 -dihexylfluorene)-alt-2,8-(5,11-di(2-ethylhexyl)-indolo[3,2-b]carbazole)) (PF-m-In) were synthesized by palladium-catalyzed Suzuki coupling polymerization and characterized for the applications of light-emitting diodes and field effect transistors (FET). The incorporation of indolocarbazole into polyfluorene could not only enhance hole transporting properties but also thermal properties. The para-linkage, PF-p-In, facilitates -electron delocalization and thus has a lower optical band gap and a higher emission maximum than those of the meta linkage, PF-m-In. The electroluminescence devices based on PF-p-In and PF-m-In as the emissive layer show a similar maximum luminance but with different emissive colors of green and blue, respectively. The FET hole mobilities of PF-p-In and PF-m-In are 6:73 Â 10 À5 and 1:50 Â 10 À4 cm 2 /VÁs, respectively, which are significantly higher than that of polyfluorene. The present study demonstrates the electronic and optoelectronic properties of polyfluorene enhanced by incorporating hole transporting indolocarbazole with different linkages.KEY WORDS: Functional Polymers / Polymer Synthesis / Light-Emitting Diodes / Field Effect Transistors / Fluorene / Indolocarbazole / Conjugated polymers have been extensively studied for various electronic and optoelectronic devices, such as electroluminescence displays, photovoltaic cells, and field effect transistors.1-5 Oligo-and polyfluorene as well as their derivatives are excellent candidates for optoelectronic applications because they exhibit high thermal/chemical stability, excellent fluorescence quantum yields, and solution processibility.6,7 However, the relatively high ionization potential and low electron affinity of poly(9,9-dialkylfluorene) lead to poor carrier injection from the electrodes. Thus, limited electroluminescence (EL) efficiency and insignificant or no field effect mobility were reported in the literature. 8,9The electronic and optoelectronic properties of polyfluorene could be improved through the approaches of copolymer, blend, side chain modification, end-capping, or nanofiber and result in enhanced device characteristics. [8][9][10][11][12][13][14][15][16][17] For example, the copolymers of fluorene with hole transporting moieties of phenothiazine and phenoxazine led to enhanced EL characteristics 8 and field effect mobility, 9 respectively. The incorporation of acceptor and donor-acceptor-donor moiety into polyfluorene also successfully improved the EL or FET characteristics.12-15 Indolocarbazole-based materials have emerged as new p-type organic semiconductors due to relatively high hole-transporting mobility and photo-oxidative stability. Relatively high hole mobilities of 0.2 and 0.02 cm 2 V À1 s À1 were reported for the indolo[3,2-b]carbazole [18][19][20] and polymer derivatives, 21-23 respectively. Hence, it would be of interest to explore the synthesis and...

Synthesis of Linearly Fused Benzodipyrrole Based Organic Materials

“…Chen et al copolymerized both 2,8-dibromo-indolo[3,2- b ]carbazole 103 and 3,9-dibromoindolo[3,2- b ]carbazole 103 with 9,9-dibutyl-fluorene 104 to obtain copolymers 105 (Scheme 29) with absorption peaks (in THF) at 357 nm (2,8-isomer) and 392 nm (3,9-isomer). Photoluminescence was at 437 nm and 457 nm respectively (in THF) [74].…”

Indolo[3,2‐b]carbazole‐based poly(arylene vinylene)s. The influence of substitution position on spectroscopic and electrochemical properties

“…It contains an indole unit fused to the 2,3‐positions of one of the benzenoid rings of the carbazole moiety and the two nitrogen atoms are ex situ to each other yielding a rigid and coplanar structure with more extended conjugation, stronger electron‐donating character and higher charge carrier mobility compared to carbazole . Functionalized ICZs are used as building blocks for the synthesis of new hole‐transport materials having good thermal and photochemical stability and applications in electrophotography, organic field effect transistors, organic light‐emitting diodes, photovoltaic solar cells and dye‐sensitized solar cells …”

“…Thus, the structure of ICZ moiety allows the introduction of functional groups in many possible positions and to obtain polymers having ICZ skeleton covalently linked at different sites. The [3,2‐b] ICZ isomer is disubstituted at carbons 2,8 or 3,9 which are analogous with carbazole's 3,6‐ and 2,7‐positions, respectively. When ICZ is synthesized from indole and aldehyde, positions 6 and 12 of the ICZ are substituted and the nature of substituents is imposed by the aldehyde used in the condensation .…”

New poly(4,4′-dicyano-4″-vinyl-triphenylamine) host material for single-layer Ir complex phosphorescent light-emitting devices

“…They have the advantage of large-area low-cost fabrications through solution processing, such as spin casting, screen printing or inkjet printing. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] However, the upper limit on the internal quantum efficiency of organic light-emitting diode or polymer light-emitting diode for electroluminescence is generally limited to 25% owing to the forbiddance of radioactive decay of triplet exciton. Phosphorescent materials based on heavy-metal complexes are particularly attractive, as both singlets and triplets can be harvested for light emission, approaching near 100% internal quantum efficiency.…”