Efficient non-doped sky-blue fluorescent organic light emitting devices based on cyanopyridine-containing anthracene derivatives

Two new cyanopyridine-containing anthracene derivatives with asymmetrical donor-π-acceptor (D-π-A) molecule structure have been successfully synthesized by Suzuki coupling reaction, namely 4-(10-(9-phenyl-9H-carbazol-3-yl)anthracen -9-yl)benzonitrile (3CzAnPyCN) and 4-(10-(4-(9H-carbazol-9-yl)phenyl)anthracen -9-yl)benzonitrile (pCzAnPyCN). The non-doped organic light emitting devices (OLEDs) using 3CzAnPyCN and pCzAnPyCN as emitters simultaneously achieved high efficiency stable sky-blue luminescence, corresponding to the maximum external quantum efficiency (EQE) of 8.07% and 8.13% with the Commission International de L'Eclairage (CIE) coordinates of (0.18, 0.35) and (0.16, 0.24), respectively. In addition, extremely low efficiency roll-offs were also evaluated in this work. The EQE values remained as high as 7.80% and 7.88% at the luminance of 1000 cd/m2, 7.31% and 6.95% at the luminance of 10000 cd/m2 for 3CzAnPyCN and pCzAnPyCN, respectively. It is found, by photophysical experiments and density functional theory analysis, that the excited state property of the luminogens revealed that the “hot excitons” induced reverse intersystem crossing (RISC) played a crucial role in improving efficiency. Such an excellent electroluminescence (EL) performance achieved in these non-doped OLEDs is among the highest values based on sky-blue fluorescent materials, potential for future optical applications.