Synthesis and chemosensory application of water-soluble polyfluorenes containing carboxylated groups.

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.

Water-soluble 1,2,4-triazole with diethylene glycol monoethyl ether groups: synthesis, characterization and application as an electron injection layer for PLEDs.

We designed a novel electron injection material 3OTAZ composed of an aromatic 1,2,4-triazolyl core with three diethylene glycol ether groups to enhance electroluminescence of PLEDs using the environmentally stable aluminum cathode. Multilayer PLEDs [ITO/PEDOT:PSS/HY-PPV/EIL(3OTAZ)/Al] using 3OTAZas an electron injection layer (EIL) exhibit significantly enhanced device performance. The maximum luminous power efficiency and maximum luminance of the device with 3OTAZ as the EIL were enhanced to 0.34 lm W(-1) and 2970 cd m(-2), respectively, compared with those without an EIL (0.006 lm W(-1), 230 cd m(-2)). The turn-on voltage was also significantly reduced from 8.2 V to 4.3 V simultaneously. The performance enhancement has been attributed to improved electron injection which has been confirmed by the increase in the open-circuit voltage (V(oc)) obtained from photovoltaic measurements. Moreover, more balanced charge injection and transport has been achieved by inserting 3OTAZ which adjusts the hole-blocking effect investigated by hole-only devices. The results indicate that 3OTAZ is an excellent electron injection candidate for performance enhancement of PLEDs using the high work-function Al cathode.

A fluorene-based material containing triple azacrown ether groups: synthesis, characterization and application in chemosensors and electroluminescent devices.

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.

Water/alcohol soluble electron injection material containing azacrown ether groups: synthesis, characterization and application to enhancement of electroluminescence.

Using an environmentally stable metal as the cathode in a polymer light-emitting diode (PLED) is an essential requirement for its practical application. We present the preparation of a water/alcohol soluble copoly(p-phenylene) (P1) containing pendant azacrown ether and ethylene glycol ether groups as a highly efficient electron injection layer (EIL) for PLEDs, allowing the use of environmentally stable aluminum as the cathode. Multilayer PLEDs [ITO/PEDOT:PSS/PF-Green-B/EIL/Al] using P1 as EIL exhibit significantly enhanced device performance, particularly in the presence of K2CO3 or Cs2CO3. The maximum luminous power efficiency and maximum luminance of the device with Cs2CO3-doped P1 as EIL were enhanced to 9.16 lm W(-1) and 17,050 cd m(-2), respectively, compared with those without EIL (0.16 lm W(-1), 890 cd m(-2)). The turn-on voltage was also significantly reduced from 5.7 V to 3.7 V simultaneously. The performance enhancement has been attributed to improved electron injection which has been confirmed by the rise in open-circuit voltage (Voc) obtained from photovoltaic measurements. The incorporation of such an electron injection layer significantly enhances device performance for PLEDs with an environmentally stable metal as the cathode.

Solution-processable hole-transporting material containing fluorenyl core and triple-carbazolyl terminals: synthesis and application to enhancement of electroluminescence.

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.