Due to the energy gap law, the direct fabrication of efficient organic afterglow materials with long emission wavelengths at ambient conditions remains challenging. Here, luminescent dopants with moderate k RISC values of 10 0 -10 1 s −1 are designed to harvest triplet energies, simultaneously improving afterglow efficiency and maintaining emission lifetimes >0.1 s. Organic matrices with large dipole moments are selected to populate the triplet excited states of the luminescent dopants and suppress their nonradiative decay and quenching. The dopant-matrix systems exhibit TADF-type organic afterglow with quantum efficiency of 20% to 60% and emission wavelengths exceeding 600 nm. Because of their singlet excited state nature, the TADF-type afterglow emitters can efficiently transfer excited energy to rhodamine B or cyanine 5.5 fluorescence dyes for the construction of red and near-infrared afterglow materials which display promising bioimaging applications.
A two-component design strategy developed by us and other research groups, where a second component is used to control the triplet excited state properties of the luminescent component (the first component), has been shown to allow a flexible choice of building blocks to prepare high-performance afterglow materials with intriguing properties. Here, we report the realization of intense organic afterglow and diverse functions by extending this two-component strategy to dopant-matrix systems, which feature small k F , small k P , and very small k nr + k q . With coronene molecules and deuterated coronene being fixed as luminescent dopants, variation of organic matrices reveals that either small-molecule organic matrices or polymeric matrices can be used to accommodate coronene molecules and largely reduce k nr + k q values, leading to the emergence of very bright organic afterglow at ambient conditions. The obtained coronene-matrix materials have been found to be readily processed into desired shapes, large-area thin films, and aqueous afterglow dispersions by melt casting and other techniques, function as efficient afterglow donors for the fabrication of red afterglow materials, and exhibit promising time-gated bioimaging functionality to avoid interference from strong fluorescence backgrounds.
We report an unexpected long room-temperature phosphorescence lifetime of up to 1.0 s by doping iodinated difluoroboron(iii) β-diketonate (IBF2) into phenyl benzoate matrices. In contrast, IBF2 powders alone show insignificant afterglow even at 77 K.
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