Regulating Spatial Configuration in Donor‐π‐Acceptor for through‐Space Exciton Transfer: Concentration‐Independent Emitter for OLEDs

Abstract Thermally activated delayed fluorescence (TADF) emitters have garnered much attention due to 100% exciton utilization and toxic metal‐free design but often experience concentration‐quenching, requiring dispersion into the host matrix. Developing emitters that maintain consistent performance and emission wavelength irrespective of the concentration remains a significant challenge. Herein, two TADF emitters (2BPy‐ p TC and 2BPy‐ o TC) are designed and synthesized. The nature and energetics of the lowest excited singlet ( S 1 ) and triplet ( T 1 ) along with the extent of through‐bond exciton transfer (TBET) and through‐space exciton transfer (TSET) are unveiled using reliable quantum‐chemical calculations. While 2BPy‐ p TC exhibits pre‐dominantly TBET, a greater extent of TSET is found in 2BPy‐ o TC. Both emitters show a low singlet‐triplet energy gap ( ΔE ST ), 0.21 eV for 2BPy‐ p TC and 0.02 eV for 2BPy‐ o TC. For 2BPy‐ p TC, increasing the emitter concentration from 5 to 100 wt.% causes a bathochromic shift in the electroluminescence (EL) peak (467 to 495 nm) and a drop in maximum external quantum efficiency ( EQE max ) from 12.0% to 5.5%. In contrast, 2BPy‐ o TC maintains EL maxima of 500 nm and consistent EQE max (24.0% – 27.2%) while increasing emitter concentration, acting as a universal emitter for both doped and non‐doped OLEDs and eliminating the need for tedious co‐deposition.