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.