High-efficiency deep-red organic radical crystals and OLEDs with solid-state fluorescence and excellent photostability

Abstract

The stable and luminescent neutral organic radicals have been attractive molecular building blocks for material science with their doublet state nature and luminescent feature, but an existing-problem caused by aggregation caused quenching (ACQ) is being counted as a priority in materials application. Here, we reported the solid-state luminescent properties of radical (4-N-carbazolyl-2,6-dichlorophenyl)bis(2,4,6-trichlorophenyl)methyl (TTM-1Cz) by precisely doping it into its precursor (4-N-carbazolyl-2,6-dichlorophenyl)bis(2,4,6-trichlorophenyl)methane (HTTM-1Cz) matrix. As a result, the photoluminescence quantum yield (PLQY) of the 2.5 wt% radical-doped film was up to 38.4%. More importantly, 1 wt% radical-doped crystals showed intense PLQY of 79.0% with elongated fluorescence lifetime of 50.4 ns and 12.5-fold longer photostability than that in n-hexane solution of pure TTM-1Cz. Furthermore, external quantum efficiency (EQE) of the 2.5 wt% radical-doped OLED device reached to 10.5% with deep red emission, which is one of the highest values for TTM-1Cz radical-based OLEDs. • Aggregation caused quenching (ACQ) problem of the luminescent neutral organic radicals was solved through precisely pre-doping the radical TTM-1Cz into its precursor HTTM-1Cz. • Photoluminescence quantum yield (PLQY) of the 2.5 wt% radical-doped film was up to 38.4%. • PLQY of the 1 wt %-doped crystal reached to 79.0%, and showed 12.5-fold longer photostability than that in n -hexane solution of pure TTM-1Cz. • The external quantum efficiency (EQE) of the 2.5 wt% radical-doped OLED device reached to 10.5% with deep red emission.