Solution-processed triphenylethylene-fluorene fluorochromes toward deep-blue organic light-emitting diodes: benefits of preventing radical formation

Abstract

High band exciton is easily trapped and quenched by the defect structure in wide bandgap light-emitting conjugated materials (LCMs), which is harmful to the performance and stability of deep-blue organic light-emitting diodes (OLEDs). In fact, an unsaturated aromatic unit is an unstable segment that is easily attacked by external influence to form organic radical, which may cause a complicated photophysical property that reduce the efficiency and stability of OLEDs. Herein, two triphenylethylene-fluorene LCMs (F-TrPE-MC₈ and M-TrPE-MC₈) are obtained with an efficient deep-blue emission toward deep-blue OLEDs. First, two materials present deep-blue emission with high efficiency of nearly 80% in the solid state, which is associated with their intramolecular singlet exciton behavior, according to time-resolved transient spectroscopy. However, unsaturated double bonds are easily activated by the synergistic effect of light and oxygen, resulting in the formation of organic radicals in solid films. These organic radicals may trap and quench the singlet exciton and further cause relatively low emission efficiency. Finally, compared to the device based on the aged film under light excitation, OLEDs based on pristine spin-coated films exhibited a better device performance and more stable deep-blue emission (0.16, 0.09), confirming the importance of the suppression of organic radicals in LCMs.