Phenanthroimidazole Derivative as an Easily Accessible Emitter for Non-Doped Light-Emitting Electrochemical Cells

We report a versatile approach to harvest electroluminescence from a nondoped light-emitting electrochemical cell (LEC) using an easily accessible phenanthroimidazole derivative. The authors investigated two different types, (i) ionic and (ii) neutral phenanthroimidazole derivatives by modifying our previously reported LEC emitter. Sky-blue electroluminescence was achieved by applying these modified emitter in LEC devices. In comparison to the parent molecule, a highly contrasting performance was exhibited by all the modified emitters except the neutral butyl derivative (nbpypn). By employing an ionic molecule (ihpypn) in a fully solution-processed typical LEC device structure, a peak brightness of 711 cd/m² was observed at a current efficiency of 0.18 cd/A. Our champion device (ihpypn-LEC) presented a 5-fold increase in maximum brightness at a ten times higher current density than its parent molecule. These peak brightness values are among the best comparing to those reported for LECs with the corresponding emission colors. Even though the neutral molecules did not show any high electroluminescence, their current efficiency at maximum brightness has improved 20 times when compared to its parent molecule utilized device. The study reveals that substituents on imidazole nitrogen has a critical impact on its performance in the LEC devices. This result is even more encouraging, considering that our molecular design can be applied to the majority of the imidazole derivatives and may open-up a plausible way of enriching the library of emitters for LECs with efficient and easily obtainable small organic molecules.