Organic phosphor doped thermoplastics with ultralong and memorable room temperature phosphorescence different from crystals

Abstract

Organic room temperature phosphorescence (RTP) crystals have been extensively reported but encounter poor mechanical properties and processing and application flexibility, which inspires much interest in developing amorphous RTP polymers. However, the current RTP polymers are mainly solution-processed films, and their thermoplasticity and shape and size flexibility and retainability as well as RTP properties need to be improved. Herein, we dissolve two classes of carbazole derivatives starting from commercial (CCZ) and self-made (LCZ) carbazole into solution of PMMA and find the solution-processed films show very poor RTP properties, however, when they are thermoplastic processed into plastic sheets, ultralong blue-yellow dual RTP and blue RTP are observed after photo-activation, which are distinctly different from their crystal RTP. These results reveal that thermoplasticizing can not only alter dispersion states but also local environment of carbazole derivatives, enabling LCZ derivative without crystal RTP to also emit ultralong molecular RTP in polymer matrix. Since RTP generation of polymer films requires photoactivation and the photoactivated RTP patterns show ultralong memory effect, promising information storage and anti-counterfeiting is enabled. This work demonstrates that organic hetero-cyclic molecules can exhibit very interesting and unpredictable RTP properties in polymers different from crystals, opening up a vast research space and a simple processing strategy for tuning and/or enhancing RTP properties of organic doped polymers.