Geometrically isomeric Pt2Ag2 acetylide complexes of 2,6-bis(diphenylphosphino)pyridine: luminescent and vapochromic properties

Abstract

In the present study, 2,6-bis(diphenylphosphino)pyridine ((Ph₂P)₂py)-supported cis- and trans-Pt₂Ag₂ alkynyl complexes were prepared and characterized by X-ray crystallography. Although the cis-Pt₂Ag₂ complexes are slightly emissive at ambient conditions, the trans-Pt₂Ag₂ complexes exhibit moderate photoluminescence in dichloromethane and have strong emission in the solid state, originating from aromatic acetylide to (Ph₂P)₂py ligand-to-ligand charge transfer (³LLCT) and Pt₂Ag₂ cluster metal-centered (³MC) triplet states. Remarkably, the trans-Pt₂Ag₂ complex [Pt₂Ag₂{(Ph₂P)₂py}₂(CCC₆H₅)₄](SO₃CF₃)₂ exhibit remarkable luminescent vapochromism with emission red-shifts of 100 nm in response to MeCN vapor, arising from intramolecular structural conversion from staggered to parallel arrangements of two face-to-face Pt(CCC₆H₅)₂ moieties, which results in the alteration of the excited-state energy in the solid state as supported by TD-DFT studies.