Deep-red electro-fluorescence based on an excimer emission with hot-exciton channels

Abstract

Red and deep-red fluorescent materials are broadly applied in many fields, such as organic light emitting diodes (OLEDs), biological imaging and night-vision devices. In this work, we designed and synthesized two orange to red emissive donor-acceptor (D-A) materials, DMAC-NZP and DMAC-NZC, in which DMAC-NZC possesses an extra cyano group. The DMAC-NZC aggregate demonstrates a large red-shift of 60 nm compared with DMAC-NZP, which can be assigned to the formation of discrete dimer and excimer emissions in its single crystal and neat films, respectively, upon cyano-substitution. Both DMAC-NZC and DMAC-NZP exhibit a maximum external quantum efficiency (EQEmax) of over 4% and a very small efficiency roll-off in doped OLEDs. More importantly, the non-doped OLEDs of DMAC-NZC show deep-red electrofluorescence at 688 nm with a considerably high exciton utilization efficiency (EUE) of 55%-82%. This work not only gives a new functional group for the construction of deep-red pure organic efficient excimer materials, but also further verifies that the “hot exciton” theory can also be effective in the excimer-based OLEDs.