Novel ter(9,9-diarylfluorene)s were synthesized by a Suzuki-coupling reaction of 2-bromofluorene (1) and 2,7-fluorenediboronic ester derivatives (3) with high isolated yields (63-86%). The X-ray structure analysis of ter(9,9'-spirobifluorene) (4aa) revealed that the conjugated chromophore adopts a helical conformation. This conformation effectively releases the steric interaction between the fluorene moieties and prevents inter-chromophore interactions. The introduction of aryl groups at the C9 position of fluorene was highly beneficial to the thermal and morphological stability of these oligomers. These terfluorenes exhibit intense blue fluorescence with excellent quantum yields both in solution ( approximately 100%) and in solid state (66-90%), and possess interesting reversible redox properties. Highly efficient blue light-emitting OLED devices were fabricated using 4aa and 4cc as emitters as well as hole transporters. The devices exhibit low turn-on voltage ( approximately 3 V) and high EL external quantum efficiency (2.5-3%).

A high-reflectivity bottom anode is essential for high-performance top-emitting organic light-emitting devices (OLEDs). Ag has the highest reflectivity for visible light among all metals, yet its electronic properties are not ideal for anodes of OLEDs. In this letter, we report that by inducing a thin silver oxide at the surface of Ag, hole injection from Ag anodes into OLEDs is largely enhanced yet with rather high reflectivity retained. Top-emitting devices using such surface-modified Ag anode show device characteristics competitive with those of a bottom-emitting device using the indium tin oxide anode.

Top-emitting organic light-emitting devices ͑OLEDs͒ have a few technical merits for active-matrix OLED displays. Generally stronger microcavity effects inherent in top-emitting OLEDs, however, complicate optimization of device efficiency and other viewing characteristics. In this letter, using the rigorous classical electromagnetic model, we analyze emission characteristics of top-emitting OLEDs as a function of device structures. From the comprehensive analysis, trends in the dependence of emission characteristics on device structures are extracted, and accordingly, a general methodology for optimizing viewing characteristics of top-emitting OLEDs for display applications is suggested. The effectiveness of the analysis and the methodology is confirmed by experimental results.