Luminescence color change of [3,4-difluoro-2,6-bis(5-methyl-2-pyridyl)phenyl-κ3N,C1,N′]cyanidoplatinum(ii) by aggregation

Abstract

We have investigated the color and luminescence color changes of novel Pt(L)CN (L = 4,6-difluoro-1,3-di(2-(4-methyl)pyridyl)benzene) in solution and crystalline states that resulted from aggregation-induced emission (AIE). In the solution state, the AIE results from excimer and trimer formation in the excited states at high concentrations. We determined the emission lifetimes of the excimer and trimer to be τ_E = 1.72 μs and τ_T = 0.43 μs, respectively, and the emission quantum yields to be ϕ_E = 20% and ϕ_T = 12%, respectively, which are slightly smaller yet comparable to τ_M = 8.85 μs and ϕ_M = 67% of the monomeric species. In the crystalline state, the purple color of Pt(L)CN with no solvent of crystallization changes to red upon exposure to chloroform vapor, and the invisible emission turns to bright red emission. This phenomenon can be applied to inexpensive devices for the fast chloroform detection. The exposure of purple crystals to dichloromethane vapor causes a further redshift of the invisible emission and blue coloration, which suggests the capability of the discrimination of chloroform from dichloromethane.