Ultraviolet-violet electroluminescence from highly fluorescent purines

We report efficient ultraviolet (UV)-violet organic light-emitting devices (OLEDs) based on highly fluorescent donor-acceptor purine molecules, which can generate tunable emission from 350 nm to 450 nm in solution by using different electron donor and acceptor arrangements on the heterocycles as reported previously. Here, external quantum efficiencies (EQEs) up to eta(EQE) = 1.6% are achieved for the multilayer OLEDs based on purine 2, with UV emission peaked at 393 nm, as compared to previously reported purine 1 based OLEDs with eta(EQE) = 3.1% and peak emission at 433 nm. The efficiencies of the OLEDs based on the two purine molecules are among the highest reported to date with emission peak wavelengths below 450 nm. By using a range of charge transport and host materials, we show that appropriate energy level alignment in multilayer OLED devices is imperative to achieve UV emission and prevent undesired emission from other layers or interfaces.