The third strategy: modulating emission colors of organic light-emitting diodes with UV light during the device fabrication process.

The modulation of emission color is one of the most critical topics in the research field of organic light-emitting diodes (OLEDs). Currently, only two ways are commonly used to tune the emission colors of OLEDs: one is to painstakingly synthesize different emitters with diverse molecular structures, the other is to precisely control the degree of aggregation or doping concentration of one emitter. To develop a simpler and less costly method, herein we demonstrate a new strategy in which the emission colors of OLEDs can be continuously changed with UV light during the device fabrication process. The proof of concept is established by a chromene-based Ir(iii) complex, which shows bright green emission and yellow emission before and after UV irradiation, respectively. Consequently, under different durations of UV irradiation, the resulting Ir(iii) complex is successfully used as the emitter to gradually tune the emission colors of related solution-processed OLEDs from green to yellow. Furthermore, the electroluminescent efficiencies of these devices are unaffected or even increased during this process. Therefore, this work demonstrates a distinctive point of view and approach for modulating the emission colors of OLEDs, which may prove great inspiration for the fabrication of multi-colored OLEDs with only one emitter.