Regulation of intra- and intermolecular Pt–Pt and π–π interactions of a U-shaped diplatinum complex to achieve pseudo-polymorphic emissions in solution and crystalline states

Abstract

For the purpose of developing multicolor emissive molecular materials, a U-shaped diplatinum molecular switch 1 with an N,N-dimethylurea bridge was prepared. Three forms of single crystals of 1 with yellow (1A), orange (1B), or red (1C) emission were obtained. X-ray analysis shows that the two constituent [Pt(NCN)] units can have an open (1A and 1C) or closed (1B) conformation with different modes of crystal packing. In particular, intermolecular Pt–Pt interaction is evident for 1C with a short Pt–Pt distance of 3.226 Å. The interconversion among these crystals was triggered by external conditions, with the aid of an additional form of crystal 1D. The deep-red emissive crystal 1C exhibits excellent photophysical properties with λ_max,emi of 650 nm, Φ of 36%, and τ of 846 ns. Spectroscopic analysis supports the hypothesis that compound 1 has a dominant open conformation in CHCl₃ and a closed conformation in MeOH solution. The conformational switching and the degree of intermolecular interaction with tunable emission colors can be regulated by solvent composition.