A fluorescence–phosphorescence dual-emissive Cu3(pyrazolate)3 complex with highly tunable emission colours for anticounterfeiting and temperature sensing

Abstract

A fluorescence–phosphorescence dual-emissive Cu₃pyrazolate₃ (Cu₃Pz₃) complex is reported here, whose ligand is a product of Diels–Alder cycloaddition between a simple anthrylpyrazole and N-phenylmaleimide. In contrast to the green-fluorescent Cu₃Pz₃ complex with the anthrylpyrazolate, the dual-emissive complex exhibits a switching between blue fluorescence and orange or red phosphorescence by modulating excitation energies or temperatures, although the intermolecular Cu–Cu distance (2.953 Å at 100 K) is remarkably shorter than those of most of the phosphorescent Cu(I) cyclic trinuclear complexes (CTCs). Based on theoretical investigations, the origins of distinct luminescence behaviors of these two complexes have been clarified as the different contributions from ligand-based orbitals in the frontier orbitals of the complexes, leading to the ligand-based fluorescence of both complexes and the metal-sensitized ligand-localized phosphorescence of the dual-emissive complex. Finally, an anticounterfeiting code and a luminescent molecular thermometer have been simply fabricated utilizing the dual-emissive Cu(I) complex. Therefore, Diels–Alder cycloaddition can be a convenient and feasible way to functionalize a given pyrazole ligand for enriching the luminescence behaviors of Cu₃Pz₃ complexes, which usually demonstrate yellow-to-red phosphorescence.