Blue electrophosphorescence in organic light‐emitting diodes (OLEDs) is enhanced by the use of 3,6‐bis(triphenylsilyl)carbazole (see figure). This carbazole derivative with sterically bulky and large‐gap triphenylsilyl groups is an electrochemically and morphologically stable efficient host material for blue electrophosphorescence. When utilized in OLEDs, high efficiencies of up to 16 %, 30.6 cd A–1, and 26.7 lm W–1 are achieved.

The synthesis and photophysical, electrochemical, and spectroelectrochemical characterization of a novel donor-acceptor (D-A) bichromophore system composed of two D-A segments linking through a spiro center are reported. The electron-donating (D) moieties are triphenylamine (TPA) groups, whereas the electron-withdrawing (A) moieties are cyano groups. The particular "spiro" configuration that perpendicularly bonds the D-A chromophores by a tetrahedral carbon, impedes orbital interactions between the branches. Thus, the two TPA substituents act independently, rendering an efficient electropolymerization process feasible. The polymer film obtained showed reversible electrochemical oxidation accompanied by strong color changes with high coloration efficiency and contrast ratio, which can be switched by potential modulation. The remarkable electrochromic behavior of the film is clearly interpreted on the basis of spectroelectrochemical studies. A plausible polymerization mechanism involved with the TPA dimerization reaction is proposed for the electropolymerization process.

An efficient and morphologically stable pyrimidine-containing spirobifluorene-cored oligoaryl, 2,7-bis͓2-͑4-tert-butylphenyl͒pyrimidine-5-yl͔-9,9Ј-spirobifluorene ͑TBPSF͒, as an emitter or a host for blue organic light-emitting devices ͑OLEDs͒, is reported. The steric hindrance inherent with the molecular structure renders the material a record-high neat-film photoluminescence ͑PL͒ quantum yield of 80% as a pure blue emitter ͑PL peak at 430 nm͒ of low molecular weight, and a very high glass-transition temperature (T g) of 195°C. Blue OLEDs employing this compound as the emitter or the emitting host exhibit unusual endurance for high currents over 5000 mA/cm 2. When TBPSF is used as a host for perylene in a blue OLED, maximal brightness of ϳ80 000 cd/m 2 had been achieved, representing the highest values reported for blue OLEDs under dc driving.

Carbazole-based materials adopting the nonconjugated substitution of triphenylsilyl (-SiPh(3)) and trityl (-CPh(3)) side groups are studied as high-triplet-energy, morphologically, and electrochemically stable host materials with tunable carrier-transport properties for organic blue electrophosphorescence. The developed host materials 9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole (CzSi), 9-(4-tert-butylphenyl)-3,6-ditrityl-9H-carbazole (CzC), and 9-(4-tert-butylphenyl)-3-(triphenylsilyl)-6-trityl-9H-carbazole (CzCSi) all show high triplet energies of 2.97-3.02 eV, along with high glass transition temperatures of 131-163 degrees C and superior electrochemical stability. Nevertheless, the carrier-transport properties show rather significant dependence on different substitutions. Although three different host materials give similar peak electroluminescence efficiencies at low driving currents, the CzSi host, which has more suitable carrier-transport properties, renders broadened distributions of the triplet excitons in phosphorescent devices, reducing the quenching associated with triplet-triplet annihilation and giving larger resistance against efficiency roll-off at higher brightnesses.