New universal bipolar host materials with fluorene as non-conjugated bridge for multi-color electrophosphorescent devices

Two novel bipolar hosts (CzFCN2 and CzDFCN) comprising a hole-transport carbazole donor and electron-transport cyano-substituted fluorene acceptor have been synthesized, and their thermal, photophysical, and electrochemical properties were characterized. The non-conjugated linkage between the carbazole donor and the cyano-substituted fluorene acceptor provides excellent thermal/morphological properties and high triplet energies (ET=2.86 eV) for both CzFCN2 and CzDFCN. These bipolar hosts also exhibited reversible redox behavior, which makes them good candidates for the host material in efficient phosphorescent organic light-emitting diode (PhOLED) devices. Multi-color PhOLED devices incorporating CzFCN2 and CzDFCN as the universal host achieved maximum external quantum efficiencies (ηext) as high as 10.7, 17.0, 17.2, and 17.6% for blue, green, yellow, and red devices, respectively. In addition, three-component white PhOLEDs (WOLEDs) based on CzFCN2 and CzDFCN as host materials exhibited high color stabilities with ηext as high as 10.5 and 12.4% and power efficiencies (ηp) of 20.5 and 26.7 lm W−1, respectively.

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