Structurally Strained Red-BODIPYs for High-Color-Purity Organic Light Emitting Diodes

Boron dipyrromethene (BODIPY) fluorescent molecules are known for their high photoluminescence quantum yield (PLQY) and narrow emission. However, achieving proper deep-red narrow emission that meets BT2020 standards, along with a high PLQY, remains a critical task till date. Herein, we demonstrate the development of four red fluorescent emitters, namely, DBF-BODIPY, DFP-BODIPY, TFP-BODIPY, and PFP-BODIPY, by substituting dibenzofuranyl and fluorophenyl units at the meso-position of BODIPY respectively. As the electron-withdrawing nature of the substituents varies, it significantly alters the emission toward 619 to 635 nm with a narrow full width at half-maximum (fwhm) of 39 to 33 nm, respectively. Specifically, pentafluorophenyl substitution narrows the fwhm at the deep-red region in toluene solution with CIE coordinates of (0.70, 0.30), nearly satisfying the BT2020 standards. Among these emitters, DBF-BODIPY showed the highest PLQY of 98%. Further, thermally activated delayed fluorescence (TADF)-sensitized organic light-emitting diodes (OLEDs) based on these emitters were studied. Among the fabricated OLEDs, the DBF-BODIPY-based OLED showed an EQE_max of 17.0% with an emission maximum at 619 nm. The corresponding device exhibited a high operational lifetime (LT₉₀) of 152 h at an initial luminescence of 5000 cd/m².