Heteroctanuclear Au 4 Ag 4 Cluster Complexes of 4,5-Diethynylacridin-9-One with Luminescent Mechanochromism.

Two heteroctanuclear Au ₄ Ag ₄ cluster complexes of 4,5-diethynylacridin-9-one (H ₂ L) were prepared through the self-assembly reactions of [Au(tht) ₂ ](CF ₃ SO ₃ ), Ag(tht)(CF ₃ SO ₃ ), H ₂ L and PPh ₃ or PPh ₂ Py (2-(diphenylphosphino)pyridine). The Au ₄ Ag ₄ cluster consists of a [Au ₄ L ₄ ] ^4- and four [Ag(PPh ₃ )] ⁺ or [Ag(PPh ₂ Py)] ⁺ units with Au ₄ L ₄ framework exhibiting a twisted paper clip structure. In CH ₂ Cl ₂ solutions at ambient temperature, both compounds show ligand fluorescence at ca. 463 nm as well as phosphorescence at 650 nm for 1 and 630 nm for 2 resulting from admixture of ³ IL (intraligand) of L ligand, ³ LMCT (from L ligand to Au ₄ Ag ₄ ) and ³ MC (metal-cluster) triplet states. Crystals or crystalline powders manifest bright yellow-green phosphorescence with vibronic-structured emission bands at 530 (568sh) nm for complex 1 and 536 (576sh) nm for complex 2 . Upon mechanical grinding, yellow-green emission in the crystalline state is dramatically converted to red luminescence centered at ca. 610 nm with a drastic redshift of the emission after crystal packing is destroyed.