Ion-Radical Mediated Multi-Color Ultra-Long Afterglow Materials

Pure organic persistent room temperature phosphorescence (RTP) has shown great potential in numerous applications, ranging from information encryption and display technologies to bio-applications and beyond. In this work, a suite of multi-color long-lived RTP materials featuring distinct afterglow emissions was constructed using an ion-radical mediated approach. b[c]p/MeBPO emitted a vivid yellow afterglow centered at 560 nm with an impressively long lifetime of 860.01 ms. While compound b[a]a exhibited a near-infrared (NIR) afterglow (τ = 215.96 ms) after doping into the matrix. The transient absorption spectroscopy investigations disclosed that the observed afterglow phenomenon was fundamentally tied to the generation of radical ions rather than the exciplex. These radical ions resulted from the reduction quenching process of the triplet excited state of compound BPO by the ground state of the doping agent. A novel evaluation methodology was devised, rooted in Marcus theory, to gauge the potential of a specific dopant-matrix combination towards generating pronounced afterglow. According to this framework, the enhancement of the afterglow is directly proportional to the decrease in the activation energy (ΔG≠) associated with the electron transfer reaction occurring between the dopant and the matrix. Notably, when the ΔG≠ surpasses 30 kcal/mol, no observable afterglow occurs, as higher ΔG≠ values significantly impede the electron transfer reaction between the two components. Furthermore, the system exhibits exceptional sensitivity, with the dopant as low as 0.02‰ molar ratio between the dopant and the host material. This remarkable dependence of afterglow intensity on the dopant concentration renders the bi-component RTP system highly promising for applications requiring ultra-high sensitivity and broad-spectrum detection capabilities.