A Series of Zinc Coordination Compounds Showing Ultralong Persistent Luminescence and Reversible Photochromic Properties Via Charge Transfer

Long persistent luminescence materials have wide application prospects in the fields of optical communication, sensors, and anticounterfeiting. Recently, some researchers have proved the feasibility of charge transfer effect in the construction of visible light excited room temperature phosphorescence (RTP) materials. However, materials with electronic effects require elaborate design to exhibit long-lived phosphorescence. Herein, a series of coordination compounds based on viologen ligand HL⋅Cl (4-carboxybenzyl)-4,4′-bipyridinium chloride) and Zn2+ with benzoic acid derivatives (o-, m-, p-phthalic acid) were reported. They exhibit not only reversible photochromic properties, but also long-lived persistent phosphorescence. Three complexes possess different structures through different auxiliary ligands with different optical physical properties. Complex 1 exhibits dynamic phosphorescence emission at low temperatures. Interestingly, we synthesized the first viologen complex (complex 2) with excitation wavelength dependent fluorescence, and the emission color gradually changed from blue to red with the increase of excitation wavelength. In addition, the applications of three complexes in data encryption and anticounterfeiting are further demonstrated. This work not only presents coordination compounds with dynamic afterglow materials, excitation wavelength- and time-dependent emission properties, but also provides a new strategy for the charge transfer effect in visible light-excited RTP materials.