Achieving stable photoluminescence by double thiacalix[4]arene-capping: the lanthanide-oxo cluster core matters

Luminescence stability is a critical consideration for applying phosphors in practical devices. In this work, we report two categories of double p-tert -butylthiacalix[4]arene (H 4 TC4A) capped clusters that exhibit characteristic lanthanide luminescence. Specifically, {[Ln 4 (μ 4 -OH)(TC4A) 2 (DMF) 6 (CH 3 OH) 3 (HCOO)Cl 2 ]}· x CH 3 OH (Ln = Eu ( 1 ), Tb ( 2 ); x = 0-1) with square-planar [Ln 4 (μ 4 -OH)] cluster cores and {[Ln 9 (μ 5 -OH) 2 (μ 3 -OH) 8 (OCH 3 ) (TC4A) 2 (H 2 O) 24 Cl 9 ]}· x DMF (Ln = Gd ( 3 ), Tb ( 4 ), Dy ( 5 ); x = 2-6) with hourglass-like [Ln 9 (μ 5 -OH) 2 (μ 3 -OH) 8 ] cluster cores are synthesized and characterized. By comparing 2 and 4 , we find that several critical luminescence properties (such as quantum efficiency and luminescence stabilities) depend directly on the cluster core structure. With the square-planar [Ln 4 (μ 4 -OH)] cluster cores, 2 demonstrates high quantum yield (∼65%) and excellent luminescence stability against moisture, high temperature, and UV-radiation. A white light-emitting diode (LED) with ultrahigh color quality is successfully fabricated by mixing 2 with commercial phosphors. These results imply that high quality phosphors might be achieved by exploiting the double thiacalix[4]arene-capping strategy, with an emphasis on the cluster core structure. {Ln 4 } cores outperform {Ln 9 } cores in achieving stable photoluminescence from double thiacalix[4]arene-capped lanthanide-oxo clusters.