Efficient blue and deep blue fluorescent OLEDs based on anthracene with upper-level intersystem crossing

Abstract

Two new emitters based on anthracene core, 6-(10-phenylanthracen-9-yl)nicotinonitrile (CNPyAnPh) and 4-(10-(pyridin-2-yl)anthracen-9-yl)benzonitrile (CNPhAnPy) are designed and synthesized for realizing blue and deep blue organic light-emitting diodes (OLEDs). Both CNPyAnPh and CNPhAnPy show nearly orthogonal structures and the suppressed π-conjugation is favorable for blue and even deep blue emission. According to the theoretical calculations, small energy differences between T2 and S1 are observed in these two isomers, endowing the “hot exciton” channel. Furthermore, the S1 of CNPyAnPh possesses both locally excited (LE) and charge transfer (CT) components. By employing CNPyAnPh and CNPhAnPy as the emissive guests in the devices, their maximum external quantum efficiencies (EQEmaxs) are 4.15% and 3.71%, respectively. Thanks to the “hot exciton” and hybrid local and charge transfer (HLCT) properties, the exciton utilization efficiencies (EUEs) of the two molecules are higher than 25%, namely, 42% for CNPyAnPh and 34% for CNPhAnPy. The Commission International de l’Eclairage (CIE) coordinate of CNPhAnPy is (0.15, 0.08), approaching the National Television System Committee (NTSC) standard index for pure blue emission.