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‐pTC and 2BPy‐oTC) are designed and synthesized. The nature and energetics of the lowest excited singlet (S₁) and triplet (T₁) 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‐pTC exhibits pre‐dominantly TBET, a greater extent of TSET is found in 2BPy‐oTC. Both emitters show a low singlet‐triplet energy gap (ΔE_ST), 0.21 eV for 2BPy‐pTC and 0.02 eV for 2BPy‐oTC. For 2BPy‐pTC, 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‐oTC 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.