A series of acene-type conjugated molecules (1-5) containing 2-6 pyrazine units and up to 16 rectilinearly arranged fused aromatic rings were synthesized by condensation coupling of 1,2-diamines and 1,2-diketones. The energy gap of the molecules estimated from absorption edge decreases with an increase in molecular length, indicating the well-delocalized nature of the molecules. The cyclic voltammetry measurements suggest that the n-type properties of these ribbonlike pyrazine derivatives are dependent on the molecular length and the number of the pyrazine units. As the number of pyrazine units and the molecular length increase, the first reduction wave onset is shifted from -1.16 to -0.62 V (vs Ag/AgCl), corresponding to the LUMO energy levels of -3.24 and -3.78 eV, respectively. These molecules tend to aggregate in solution more readily with an increase in molecular length, as evident by (1)H NMR and UV-vis absorption spectra. Introduction of t-butyl groups in pyrene units can noticeably suppress the aggregation of these molecules in solution. High electron affinity, high environmental stability, and ease of structural modification make these compounds excellent candidates as a new class of n-type semiconductors.

We prepared dendritic perylene bisimide probes with triblock structures: perylene bisimides fluorescence cores, branched oligo(glutamic acid)s and polyethylene glycol chains. These probes showed good water solubility, low cytotoxicity and strong fluorescence in live cells.

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Self-host functional iridium dendrimers with N-phenylcarbazole-based polyether dendrons.

A novel series of white light emitting single polymers are prepared by incorporating low contents of quinacridone into the main chain of polyfluorene. This is the first report of quinacridone-containing conjugated polymer. Single layer devices (ITO/PEDOT:PSS/polymer/Ca/Al) are fabricated with these polymers. Energy transfer from fluorene segments to quinacridone unit is observed. Moreover, in the EL process, quinacridone unit can trap electrons and cannot trap holes from fluorene segments. Electroluminescence (EL) spectra of these polymers exhibit simultaneous blue emission (λ max ) 425 nm/445 nm) from the fluorene segments and yellow emission (λ max ) 540 nm/580 nm) from the quinacridone unit. The latter one comes from the partial energy transfer and charge trapping from the fluorene segments to the quinacridone unit. With the increase of the quinacridone unit's content in the copolymers, the relative intensity of the orange emission band in the EL spectra becomes stronger owing to the more complete energy transfer and charge trapping. For the polymer (PFQA3) with the quinacridone unit's content of 0.03 mol %, its EL spectrum shows balanced intensities of blue emission and orange emission, leading to white emission with CIE coordinates of (0.27, 0.35). Single layer device of this polymer exhibits the turn-on voltage of 3.5 V, luminous efficiency of 3.47 cd/A, power efficiency of 2.18 lm/W, external quantum efficiency of 1.33% and maximum brightness of 9062 cd/m 2 . Increase of the quinacridone unit's content results in increased turn-on voltages and decreased EL efficiencies of the resulting devices owing to the serious trap of electrons by quinacridone unit and exciton quenching of quinacridone unit at high concentration, respectively.

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A novel self-host blue-emitting iridium dendrimer, namely, B-CzPO, has been designed and synthesized via a postdendronization route, where a bipolar carbazole/triphenylphosphine oxide hybrid is selected as the peripheral dendron instead of the p-type oligocarbazole used in unipolar analogue B-CzG2. This structural modification can render B-CzPO with more balanced charge transportation relative to that of B-CzG2. As a result of the significantly reduced efficiency roll-off, the nondoped phosphorescent organic light-emitting diodes (PhOLEDs) of B-CzPO show a superior high-brightness performance, revealing a luminous efficiency of 21.2, 16.1, and 10.5 cd/A at 1000, 5000, and 10 000 cd/m, respectively. Compared with that of B-CzG2 (i.e., 7.8 cd/A @5000 cd/m), more than doubled high-brightness performance is achieved for B-CzPO. The results indicate that the design of self-host phosphorescent dendrimers with a bipolar feature will be a promising strategy to develop efficient nondoped PhOLEDs suitable for high-brightness applications including general illumination and micro displays.

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