Outstanding Circularly Polarized TADF in Chiral Cu(I) Emitters: From Design to Application in CP-TADF OLEDs

Abstract

Low-cost molecular emitters that merge circularly polarized luminescence (CPL) and thermally activated delayed fluorescence (TADF) properties are attractive for many high-tech applications. However, the design of such emitters remains a difficult task. To address this challenge, here, we propose a simple and efficient strategy, demonstrated by the design of pseudochiral-at-metal complexes [Cu(L*)DPEPhos]PF₆ bearing a (+)/(-)-menthol-derived 1,10-phenanthroline ligand (L*). These complexes exhibit a yellow CP-TADF with a record-high quantum yield (close to 100 %) and high dissymmetry factor (|g_lum|~1×10^-2). Remarkably, the above compounds also show a negative thermal-quenching (NTQ) of luminescence in the 300-77 K range. Exploiting the designed Cu(I) emitters, we fabricated efficient CP-TADF OLEDs displaying mirror-imaged CPL bands with high |g_EL| factors of 1.5×10^-2 and the maximum EQE of 6.15 %. Equally important, using the (+)-[Cu(L*)DPEPhos]PF₆ complex, we have discovered that an external magnetic field noticeably suppresses CP-TADF of Cu(I) emitters. These findings are an important contribution to the CPL phenomenon and provide access to highly efficient, low-cost and robust CP-TADF emitters.

Keywords: CP-TADF OLEDs; Circularly polarized luminescence; Negative thermal quenching; TADF emitters Magnetically sensitive luminescence.