Eight Cd(ii) coordination polymers with persistent room-temperature phosphorescence: intriguing dual emission and time-resolved afterglow modulation

Abstract

In this work, a new series of coordination polymers (CPs) 1–8 were designed and successfully synthesized; they displayed typical afterglow at room temperature under ambient conditions. In 1–4, single green phosphorescence was observed, where the T₂ (π, π*) state was stabilized by the π-stacking interactions of the phosphorescent group tynca⁻, which contributed to enhancing their luminescence lifetimes. In contrast, when the π-stacking interaction of the phosphorescent group tynca⁻ was absent in the rigid matrix, 5–8 exhibited an intriguing time-resolved afterglow modulation, in which yellow [T₁ (n, π*), short lifetime] and green [T₂ (π, π*), long lifetime] phosphorescences were sequentially observed during the decay process when the common UV light was turned off. As one of the representatives of long-lived dual phosphorescent CPs, the promising optical properties of 8 allowed it to be used in logos for advanced anti-counterfeiting systems. To the best of our knowledge, this special and rare afterglow modulation has not been reported in the literature for persistent RTP (p-RTP) CP systems, and further exploration in this area may open a new door for newly emerging technologies such as optical recording and encryption or multimodal bio-imaging.