Fang-Iy Wu

Synthesis and characterization of spiro-linked poly(terfluorene): a blue-emitting polymer with controlled conjugated length

The synthesis and characterization of a fluorene–spirobifluorene alternating copolymer, P(OF-SBF), are described. In the case of the spiro-segment, the two fluorene rings are orthogonally arranged and connected through a tetrahedral bonding carbon atom (the spiro center). As a consequence, the polymer chain periodically zigzags, with an angle of 90° at each spiro center. This structural feature not only preserves the rigidity of the polymer chain but also prevents the π-stacking of the polymer backbone, resulting in an improvement in both thermal and spectroscopic stabilities. Comparing the absorption and emission spectra of P(OF-SBF) and of a terfluorene model compound, it was revealed that P(OF-SBF) possesses a well-defined conjugation length. The polymer can serve as a host matrix to effectively transfer its excitation energy to a derivatized perylene dopant, yielding an efficient blue-light-emitting layer.

Highly efficient orange and deep-red organic light emitting diodes with long operational lifetimes using carbazole–quinoline based bipolar host materials

Orange and deep red-emitting phosphorescent organic light-emitting diodes (PhOLEDs) are important for OLED displays and lighting; however, high-performance with long operational lifetime hosts designed for orange/deep red PhOLEDs are very rare. Three new carbazole–quinoline hybrids are synthesized and used as the host materials for orange and deep-red PhOLEDs. These bipolar hosts show high glass transition temperatures of 90–146 °C and triplet energy gaps of 2.51–2.95 eV. The optimized orange PhOLEDs using 9-(4-(4-phenylquinolin-2-yl)phenyl)-9H-carbazole (CzPPQ) as the host show the highest external quantum efficiency (EQE) of 25.6% and a power efficiency of 68.1 lm W−1, which are the highest values for orange PhOLEDs. More importantly, the efficiency roll-off is extremely small for both the orange and deep-red devices. For example, an orange device showed an EQE of 25.1% at 100 cd m−2 and 23.6% at 1000 cd m−2; the result appears to be the lowest efficiency roll-off for orange PhOLEDs to date. Additionally, the operational lifetime of both the orange and deep-red devices gave a T50 of more than 26412 and 11450 h, respectively, at an initial luminance of 500 cd m−2. The values are 12 times (orange) and 6 times (red) longer than those of the corresponding devices using CBP as the host.

White organic light-emitting diodes based on 2,7-bis(2,2-diphenylvinyl)-9,9′-spirobifluorene: Improvement in operational lifetime

Very bright white organic light-emitting diodes were fabricated using 2,7-bis(2,2-diphenylvinyl)-9,9′-spirobifluorene (DPVSBF) doped with [4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran)] (DCJTB) as the emission layer. With a device configuration of ITO∕NPB(40nm)∕DPVSBF:0.2%DCJTB(11nm)∕Alq(30nm)∕LiF(1nm)∕Al(150nm), a brightness of 1575cd∕m2 with an external quantum efficiency of 3.31% and luminous efficiency of 8.00cd∕A, a power efficiency of 5.35lm∕W was achieved at a driving current of 20mA∕cm2 (4.7V). The brightness reached 66000cd∕m2 at 15V. The Commission Internationale de l’Eclairage coordinates stayed nearly constant, changed from (0.35, 0.36) to (0.32, 0.34) when the voltage increased from 6to12V. The relative operational lifetime of the device increased by a factor of ∼20 compared with a similar device based on 4,4′-bis-(2,2-diphenylvinyl)-1,1′-biphenyl as the source of the blue emission. The much extended half-lifetime was attributed to the higher morphological s...

Spirobifluorene-based pyrazoloquinolines: efficient blue electroluminescent materials

We report the synthesis of spirobifluorene-based pyrazoloquinolines, spiro-PAQ-Me and spiro-PAQ-Ph, in which two identical luminophores are connected through an sp3-hybridized carbon atom (a spiro center) and are orthogonally arranged. The incorporation of the rigid spirobifluorene linkage results in significant increases in the glass transition temperatures, which are in the range 246–280 °C. These new materials display the characteristic absorptions of the mono-pyrazoloquinoline (i.e. non-spiro) derivatives, each with a broad, low-energy absorption at ca. 420 nm, and emit photoluminescence efficiently in the blue region. Electrochemical studies reveal that these compounds exhibit reversible reductions and low-lying LUMO energy levels that originate from the electron-deficient nature of the pyrazoloquinoline ring. Multilayer organic electroluminescent devices constructed using spiro-PAQ-Ph as a dopant in the emitting layer produced bright blue emissions with maximum luminescence exceeding 20 000 cd m−2. For the 2.0%-doped device, a high external quantum efficiency of 3.6% (4.5 cd A−1, 2.02 lm W−1) was achieved at 20 mA cm−2 and 7.0 V with color coordinates of (0.14, 0.17).

Synthesis and photo- and electroluminescence properties of 3,6-disubstituted phenanthrenes: alternative host material for blue fluorophores.

Three deep-blue fluorescent 9,10-bis(4-tert-butylphenyl)phenanthrenes with diphenyl, -naphthyl, and -pyrenyl moieties at C3 and C6 positions were synthesized and used as the host for doped blue fluorescent devices; one of these devices reveals excellent external quantum efficiency of 7.7% and current efficiency of 9.8 cd A(-1) with low efficiency roll-off, deep-blue color coordinates (0.14, 0.14) and long operational lifetime.