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A novel solution-processable, efficient hole-transporting material 2,4,7-tri[2-(9-hexylcarbazole)ethenyl]-9,9-dihexylfluorene (FC), composed of a fluorenyl core and triple-carbazolyl terminals, is successfully synthesized and well characterized. The FC is a thermally stable, amorphous material because of its aromatic and asymmetric structure. The highest occupied molecular orbital (HOMO) level of FC is -5.21 eV, as determined by cyclic voltammetry, implying its applicability as a hole-transporting layer (HTL) to promote hole injection. Furthermore, the FC could be deposited by a spin-coating process to obtain a homogeneous HTL film, more convenient and cost-effective than conventional NPB which must be deposited by vacuum vapor deposition. When fabricated as multi-layer OLED [ITO/PEDOT:PSS/HTL(25 nm)/Alq3(50 nm)/LiF(0.5 nm)/Al(100 nm)], the maximum brightness (21,400 cd m(-2)) and current efficiency (3.20 cd A(-1)) based on the FC are superior to those using conventional NPB as the hole-transporting layer. In addition, a homogeneous FC film is readily prepared by simple wet processes (spin-coating). Our results indicate that the FC is a promising optoelectronic material which is readily processed by wet methods such as spin-coating.

We have designed a novel bipolar material (FTzCz) consisting of spiro-fluorenyl terminals and a bipolar core to enhance emission efficiency of phosphorescent light-emitting diodes based on a conventional poly(9-vinylcarbazole) host and Ir(ppy) 3 dopant. The core is composed of directly linked hole-transporting carbazolyl and electron-affinitive aromatic 1,2,4-triazolyl groups. The bipolar FTzCz was synthesized by the Suzuki coupling reaction and was well characterized. It exhibited not only good thermal stability due to its rigid and non-planar chemical structure, but also facilitated hole-and electron-affinities simultaneously. Blending the bipolar FTzCz with PVK significantly enhanced the performance of electrophosphorescent devices [ITO|PEDOT:PSS|(PVK + FTzCz):Ir(ppy) 3 (4 wt%)| BCP (10 nm)|Ca (50 nm)|Al (100 nm)]. The maximum luminance and maximum luminance efficiency were enhanced from 3550 cd m À2 and 5.6 cd A À1 (neat PVK-based device) to 4510 cd m À2 and 9.9 cd A À1 (blend device with PVK : FTzCz ¼ 8 : 2), respectively. Our results demonstrate the efficacy of the bipolar FTzCz in enhancing performance of electrophosphorescent devices.

Two novel copoly(p-phenylene)s (P1-P2) containing bipolar groups (12.8 and 6.8 mol %, respectively), directly linked hole transporting triphenylamine and electron transporting aromatic 1,2,4-triazole, were synthesized to enhance electroluminescence (EL) of poly(p-phenylene vinylene) (PPV) derivatives. The bipolar groups not only enhance thermal stability but also promote electron affinity and hole affinity of the resulting copoly(p-phenylene)s. Blending the bipolar copoly-(p-phenylene)s (P1-P2) with PPV derivatives (d6-PPV) as an emitting layer effectively improve the emission efficiency of its electroluminescent devices [indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) (PEDOT):poly(styrenesulfonate) (PSS)/poly-mer blend/Ca (50 nm)/Al (100 nm)]. The maximum luminance and maximum luminance efficiency were significantly enhanced from 310 cd m À2 and 0.03 cd A À1 (d6-PPV-based device) to 1450 cd m À2 and 0.20 cd A À1 (blend device with d6-PPV/P1 ¼ 96/4 containing $0.5 wt % of bipolar groups), respectively. Our results demonstrate the efficacy of the copoly(p-phenylene)s with bipolar groups in enhancing EL of PPV derivatives. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 5727-5736, 2010

Enhancing electroluminescence of conventional MEH−PPV {poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene]} is desirable due to its popularity in polymeric emitting materials. The enhancement is much readily attained by simple blending with functional polymers instead of tedious structural modification. In response to this, three copolyfluorenes (P1−P3) containing bipolar groups (3.1−11.2 mol %), directly linked hole-transporting triphenylamine and electron-transporting 1,2,4-triazole, are synthesized by Suzuki coupling reaction. The bipolar groups not only suppress undesirable green emission of polyfluorene under thermal annealing but also increase hole and electron affinity of the resulting copolyfluorenes. Blending the bipolar copolyfluorenes with MEH−PPV effectively improves the emission efficiency of its electroluminescent devices [ITO/PEDOT:PSS/polymer blend/Ca(50 nm)/Al(100 nm)]. The maximum luminance and maximum luminance efficiency are significantly enhanced from 3120 cd/m2 and 0.49 cd/A (MEH−PPV device) to 19 560 cd/m2 and 1.08 cd/A (blend device with ca. 0.5 wt % of bipolar groups), respectively. Our results demonstrate the efficacy of the bipolar copolyfluorenes in enhancing electroluminescence of MEH−PPV.

Detection of metal ions in aqueous solutions is a major issue for environmental protection. Conjugated polyelectrolytes showing high sensitivity and selectivity towards the detection of metal ions are highly desirable. We report a water-soluble polyfluorene containing carboxylated groups (P1), poly[9,9'-bis(3''-propanoate)fluoren-2,7-yl] sodium salt, which shows high recognition capability toward Cu(+) and Cu(2+). P1 was prepared via the hydrolysis of poly[9,9'-bis(tert-butyl-3''-propanoate)fluoren-2,7-yl] (P0) which was synthesized by Suzuki coupling polymerization. The photoluminescence (PL) spectra of P1 in aqueous solution are significantly quenched in the presence of Cu(+) and Cu(2+). P1 shows high selectivity and sensitivity toward Cu(+) and Cu(2+), with the Stern-Volmer constants (Ksv) being 3.5 × 10(6) and 5.78 × 10(6) M(-1), respectively. Moreover, the stoichiometric ratio of the P1 repeat unit to Cu(+) or Cu(2+) is 2 : 1 obtained from Job's plot. P1 maintains high selectivity towards Cu(+) or Cu(2+) in the presence of various metal cations. Our results demonstrate that P1 shows very high sensitivity and selectivity in recognizing Cu(+) and Cu(2+), indicating that it is a promising functional material for chemical sensors.

We design a novel multifunctional fluorene-based material containing triple azacrown ether (FTC) not only for application in aqueous solution as a chemosensor towards Fe(3+) but also to enhance the electroluminescence of PLEDs using an environmentally stable aluminum cathode. The photo-physical and sensing properties were investigated by absorption and photoluminescence (PL) spectroscopy. The FTC exhibited specific selectivity and high sensitivity toward Fe(3+), with the Stern-Volmer coefficients (Ksv) being 1.59 × 10(5) M(-1) in a solvent mixture of tetrahydrofuran and water (THF-H2O = 9/1, v/v). The FTC maintained high selectivity toward Fe(3+) in the presence of ten interfering metal cations. The HOMO and LUMO levels were estimated to be -5.88 eV and -2.88 eV, respectively. The FTC significantly enhances the emission performance of PLEDs [ITO/PEDOT:PSS/MEH-PPV/EIL/Al] when used as an electron injection layer (EIL), especially in the presence of metal carbonates. Particularly, the device using K2CO3 doped FTC as the electron-injection layer (EIL) exhibited significantly enhanced performance compared to the one without EIL. The performance was significantly enhanced to 11 630 cd m(-2) and 1.47 cd A(-1), respectively, from 230 cd m(-2) and 0.03 cd A(-1) of the non-FTC device. Current results indicate that multifunctional fluorene-based material FTC is a potential candidate for selective detection of Fe(3+) and as an effective electron injection layer to enhance the performance of MEH-PPV.

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