Anion-regulated transient and persistent phosphorescence and size-dependent ultralong afterglow of organic ionic crystals

It is a formidable challenge to achieve highly efficient organic afterglow and readily tunable transient and persistent phosphorescence of organic materials because of the lack of valid design principles. Herein, we report the regulation of the transient and persistent room-temperature phosphorescence of organic ionic crystals by the alteration of anions, and the unique size-dependent ultralong afterglow of tetraphenylphosphonium perchlorate (TPP ClO4) crystals under ambient conditions. Three organic ionic crystals show sharply distinct triplet emissions based on three heavy-atom free anions by proper construction of donor-acceptor patterns in the crystals. TPP ClO4 crystals exhibit ultrabright transient phosphorescence and ultralong afterglow, and the gradual enhancement of the afterglow with the crystal size directly proves the generation of ultralong afterglow from aggregates with strong intermolecular interactions in the crystals. These results greatly contribute to the general design principles of highly efficient transient and persistent phosphorescence and their regulations by rational design. Highly sensitive detection and imaging of perchlorate ions are achieved in a phosphorescence turn-on manner based on the bright room-temperature phosphorescence of TPP ClO4 crystals, and valuable anti-counterfeiting applications of the ultralong afterglow of TPP ClO4 crystals are also demonstrated in practical examples.