Supramolecular Assembly, Solvent-Induced, and Mechanochromic Luminescence of Au(I) Quinoline-8-thiolates

AuCl(PMe₃) and AuCl(PEt₃) were used to react with quinoline-8-thiolate (8-QNS) to give three Au(I) complexes, i.e., [8-QNS(AuPMe₃)₂]ClO₄ (<b>1</b>), [(8-QNS)₂Ag(AuPMe₃)₂]ClO₄ (<b>2</b>), and [8-QNS(AuPEt₃)₂]ClO₄ (<b>3</b>), which have been structurally determined by X-ray diffraction to show various intra- and intermolecular metal···metal contacts (i.e., metal = Au(I) or Ag(I)). All complexes displayed solid-state luminescence at 535-568 nm, which is most likely attributed to an intraligand transition of 8-QNS and/or a S → Au(I) charge-transfer transition, possibly modified by Au(I)···Au(I) interactions. Notably, complex <b>1</b>·CH₂Cl₂ exhibited remarkable mechanochromic luminescence from 535 to 601 nm upon grinding. While immersed in various solvents for the ground powder samples of complex <b>1</b>·CH₂Cl₂, the luminescence at 601 nm mostly reverted to the original luminescence. Powder X-ray diffraction measurements indicated that complex <b>1</b>·CH₂Cl₂ underwent structural transformation from a crystalline to an amorphous phase upon grinding, and it can be restored to the original crystalline phase upon immersion in various solvents. Additionally, the reversible experiments of complex <b>1</b>·CH₂Cl₂ for the grinding and immersion actions were performed for up to five cycles. Moreover, the time-dependent luminescence spectra for the crystalline samples of complex <b>1</b>·CH₂Cl₂ were measured, and they showed a significant luminescence change from 535 to 590 nm within 2 days.