Flexible crystalline persistent fluorescence waveguides: a universal strategy for anti-counterfeiting and secure communication

The development of flexible organic crystals (FOCs) with persistent emissions represents a groundbreaking advancement in optoelectronic materials, offering transformative applications in flexible displays, secure communication, and anti-counterfeiting. Despite extensive efforts, achieving persistent emissions in FOCs remains a significant challenge, primarily due to the inherent limitations of organic molecular systems in stabilizing triplet excitons. Here, we report a universal and scalable strategy to enable long-lasting fluorescence in FOCs by incorporating a polymer coating doped with methyl-4-aminobenzoate within a poly(vinyl alcohol) matrix on crystalline substrates. Utilizing non-traditional phosphorescent radiative energy transfer mechanisms, this design transfers triplet energy of methyl-4-aminobenzoate efficiently to the FOCs, resulting in multicolor-tunable persistent fluorescence emissions. The coated FOCs demonstrate exceptional mechanical flexibility and maintain optical stability under repeated bending, while also exhibiting a robust persistent fluorescence waveguiding effect, even after UV excitation ceases. This work represents a significant breakthrough as it not only provides a solution for integrating long-lasting persistent fluorescence waveguiding properties into flexible organic systems but also enables precise modulation of optical features, laying the foundation for scalable applications in advanced encryption, anti-counterfeiting, and optoelectronic devices.