Showing papers by "Junwu Chen published in 2007"

Silole‐Containing Polymers: Chemistry and Optoelectronic Properties

Abstract: In this review, the synthesis and optoelectronic properties of various π-conjugated-, σ-conjugated-, pendanted-, and hyperbranched or dendritic silole-containing polymers (SCPs) are described So far, substituted silole, dibenzosilole, dithienosilole, and bis-silicon-bridged stilbene have been incorporated into SCPs The tunable bandgaps from 40-155 eV, variable fluorescent colors from UV to blue, green, and red (RGB) light, fluorescent chemo-sensors for 2,4,6-trinitrotoluene (TNT)-type explosives, aggregation-induced emission, efficient electroluminescence emissions for RGB lights, phosphorescent hosts with high triplet energy level, efficient solar cells, stable field-effect transistors with high hole mobility in air, and attenuation of strong laser power, are the important features of SCPs

Synthesis and optoelectronic properties of silole‐containing polyfluorenes with binary structures

Abstract: 2,5-Bis(2-bromofluorene-7-yl)silole was prepared by a modified one-pot synthesis with a reverse addition procedure, from which novel silole-containing polyfluorenes with binary random and alternating structures (silole contents between 4.5 and 25% and high Mw up to 509 kDa were successfully synthesized. The well-defined repeating unit of the alternating copolymer comprises a terfluorene and a silole ring. Optoelectronic properties including UV absorption, electrochemistry, photoluminescence (PL), and electroluminescence (EL) of the copolymers were examined. The different excitation energy transfers from fluorene to silole of the copolymers in solution and in the solid state were compared. The films of the copolymers showed silole-dominant green emissions with high absolute PL quantum yields up to 83%. EL devices of the copolymers with a configuration of ITO/PEDOT/copolymer/Ba/Al displayed exclusive silole emissions peaked at around 543 nm and the highest EL efficiency was achieved with the alternating copolymer. Using the alternating copolymer and poly(9,9-dioctylfluorene) as the blend-type emissive layer, a maximum external quantum efficiency of 1.99% (four times to that of the neat film) was realized, which was a high efficiency so far reported for silole-containing polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 756–767, 2007

Simple Silole-Containing Polyfluorene for White Electroluminescence with Simultaneous Blue, Green, and Red Emission

Abstract: Novel conjugated silole-containing polyfluorenes, with green- and red-emissive siloles on the backbone of the blue-emissive polyfluorene are synthesized for white light electroluminescence (EL) from a single polymer with simultaneous red, green, and blue (RGB) emission. The CIE coordinates (0.33, 0.36) of the white light EL spectra are very close to that for pure white light (0.33, 0.33). The EL spectra are also quite stable at different applied voltages or brightness. The relative intensities for the three RGB peaks, at 450, 505, and 574 nm, were 0.94, 1, and 0.97, respectively, which demonstrates a balanced simultaneous RGB emission. A maximum luminous efficiency of 2.03 cd A -1 for a brightness of 344 cd·m -2 , and a luminous efficiency of 1.86 cd A -1 for a more practical brightness of 2 703 cd m -2 , were achieved.

Synthesis and Optoelectronic Properties of Random Copolymers Derived from Fluorene and 2,5-Bis(2,1,3-benzothiadiazolyl)silole

Abstract: A novel series of soluble conjugated random copolymers (PFO-BTS) derived from 9,9-dioctylfluorene (FO) and bis(2,1,3-benzothiadiazolyl)silole (BTS) were synthesized by Suzuki coupling reactions. The feed ratios of FO to BTS were 99:1, 95:5, 90:10, and 85:15. Chemical structures and optoelectronic properties of the copolymers were characterized by elemental analysis, NMR, UV absorption, cyclic voltammetry, photoluminescence (PL), and electroluminescence (EL). The elemental analyses of the copolymers indicated that FO and BTS contents in the copolymers were very close to that of the feed compositions. Compared with the solution PL, complete PL excitation energy transfer from the PFO segments to the BTS units could be achieved by film PL at lower BTS content. The films of the copolymers exhibited PL quantum yields between 22 and 34%. EL devices with a configuration of ITO/PEDOT/PFO-BTS/Ba/Al demonstrated that the BTS units could serve as powerful exciton traps, giving orange-red EL emissions. The PFO-BTS15 was utilized to fabricate blend-type PLEDs with the PFO, the EL efficiency was improved to 1.37% with a weight ratio of PFO-BTS15 : PFO = 1 : 4.

Efficient Improvement of Fluorescence Quantum Yield of Fluoreneethynylene‐Based Polymers by Introducing a Perfluoroalkylbenzene Unit to the Polymers

Abstract: In comparison with poly(9,9-dialkylfluorene)s widely used in organic optoelectronic devices, poly(9,9-dialkylfluoreneethynylene)s (PFEs) have attracted less attention partly because of their poor fluorescence quantum yield (FQY) in the solid state. In order to improve the FQY, a 1,4-bis(perfluorohexyl)benzene (BFB) unit was introduced to PFEs, and the results showed that the absolute FQY in the solid state was dependent on the mol-% of the BFB unit in the copolymers. When mol-% was 40 and 50%, respectively, the absolute FOY had greatly increased from 4.9% of PFE to 7.8 and 17.4% of the copolymers, respectively. For comparison, a 1,4-dihexylbenzene (DHB) unit was also introduced to PFE, whereas the obtained copolymer showed the absolute FQY of 3.8%, suggesting that the DHB unit was not suitable for improvement of the FQY of PFEs. Electrochemically, the PFE containing BFB units showed lower reduction potential than that of PFE. All the fluorine-containing polymers have good thermal stability.