Achiral Au(I) Cyclic Trinuclear Complexes with High-Efficiency Circularly Polarized Near-Infrared TADF

Realizing high photoluminescence quantum yield (PLQY) in the near-infrared (NIR) region is challenging and valuable for luminescent material, especially for thermally activated delay fluorescence (TADF) material. In this work, we report two achiral cyclic trinuclear Au(I) complexes, Au-3(4-Clpyrazolate)(3) and Au-3(4-Brpyrazolate)(3) (denoted as Cl-Au and Br-Au), obtained through the reaction of 4-chloro-1H-pyrazole and 4-bromo-1H-pyrazole with Au(I) salts, respectively. Both Cl-Au and Br-Au exhibit TADF with high PLQY (>70 %) in the NIR I (700-900 nm) (?(max) = 720 nm) region, exceeding other NIR-TADF emitters in the solid state. Photophysical experiments and theoretical calculations confirmed the efficient NIR-TADF properties of Cl-Au and Br-Au were attributed to the small energy gap ?E(S1-T2) (S = singlet, T = triplet) and the large spin-orbital coupling induced by ligand-to-metal-metal charge transfer of molecular aggregations. In addition, both complexes crystallize in the achiral Pna2(1) space group (mm2 point group) and are circularly polarized light (CPL) active with maxima luminescent dissymmetry factor |g(lum)| of 3.4 x 10(-3) (Cl-Au) and 2.7 x 10(-3) (Br-Au) for their crystalline powder samples, respectively. By using Cl-Au as the emitting ink, 3D-printed luminescent logos are fabricated, which own anti-counterfeiting functions due to its CPL behavior dependent on the crystallinity.

Automated summary

In this study, two achiral cyclic trinuclear Au(I) complexes, Cl-Au and Br-Au, were synthesized and exhibited high thermally activated delay fluorescence (TADF) with a high photoluminescence quantum yield (PLQY) in the near-infrared region. The efficient TADF properties were attributed to the small energy gap and large spin-orbital coupling induced by ligand-to-metal-metal charge transfer. Both complexes showed circularly polarized light (CPL) activity and were used to fabricate anti-counterfeiting luminescent logos through 3D printing.