Lifetime-tunable organic persistent room-temperature phosphorescent salts for large-area security printing

Organic persistent room-temperature phosphorescent (RTP) materials are promising for applications requiring the secure recording and anti-counterfeiting features owing to their appealing optical properties. Several critical challenges, such as the difficulty to obtain high-quality patterns over large areas and low security levels, need to be addressed to meet the requirements for commercial purpose. Here, we prepared a series of quaternary phosphonium salts with different alkyl chains, which showed interesting organic persistent RTP. The ionic characteristics and the alkyl chains of these molecules impart abundant weak intermolecular interactions. This confers the molecules a high crystallinity, which helps to preserve the persistent RTP properties and cover large areas. Moreover, the RTP lifetime of these organic salts varies over a wide range (1.27 to 884.71 ms) and can be tuned by simply changing the alkyl chain length and counterions, which opens new possibilities in multi-level information encryption applications. It is believed that the engineering of organic salts with tunable persistent RTP lifetimes and large-area printing can promote early-stage demonstrations of security applications into mature commercialization.