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 (H₄TC4A) capped clusters that exhibit characteristic lanthanide luminescence. Specifically, {[Ln₄(μ₄-OH)(TC4A)₂(DMF)₆(CH₃OH)₃(HCOO)Cl₂]}·xCH₃OH (Ln = Eu (1), Tb (2); x = 0-1) with square-planar [Ln₄(μ₄-OH)] cluster cores and {[Ln₉(μ₅-OH)₂(μ₃-OH)₈(OCH₃) (TC4A)₂ (H₂O)₂₄Cl₉]}·xDMF (Ln = Gd (3), Tb (4), Dy (5); x = 2-6) with hourglass-like [Ln₉(μ₅-OH)₂(μ₃-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 [Ln₄(μ₄-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.