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

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 (EQE_maxs) 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.