Long-Lived Organic Room-Temperature Phosphorescence fromAmorphous Polymer Systems

Long-lived organic room-temperature phosphor-escence (RTP) materials have recently drawn extensive attentionbecause of their promising applications in information security,biological imaging, optoelectronic devices, and intelligent sensors.In contrast to conventionalfluorescence, the RTP phenomenonoriginates from the slow radiative transition of triplet excitons.Thus, enhancing the intersystem crossing (ISC) rate from thelowest excited singlet state (S1) to the excited triplet state andsuppressing the nonradiative relaxation channels of the lowestexcited triplet state (T1) are reasonable methods for realizinghighly efficient RTP in purely organic materials. Over the past fewdecades, many strategies have been designed on the basis of theabove two crucial factors. The introduction of heavy atoms,aromatic carbonyl groups, and other heteroatoms with abundant lone-pair electrons has been demonstrated to strengthen the spin-orbit coupling, thereby successfully facilitating the ISC process. Furthermore, the rigid environment is commonly constructedthrough crystal engineering to restrict intramolecular motions and intermolecular collisions to decrease excited-state energydissipation. However, most crystal-based organic RTP materials suffer from poor processability,flexibility, and reproducibility,becoming a thorny obstacle to their practical application. Amorphous organic polymers with long-lived RTP characteristics are more competitive in materials science. The intertwinedstructures and long chains of polymers not only ensure the rigid environment with multiple interactions but also protect tripletexcitons from the surroundings, which are conducive to realizing ultralong and bright RTP emission. Exploring the fabricationstrategies, intrinsic mechanisms, and practical applications of organic long-lived RTP polymers is highly desirable but remains aformidable challenge. In particular, intelligent organic RTP polymer systems that are capable of dynamically responding to externalstimuli (e.g., light, temperature, oxygen, and humidity) have been rarely reported. To develop multifunctional RTP materials andexpand their potential applications, a great amount of effort has been expended. This Account gives a summary of the significant advances in amorphous organic RTP polymer systems, especially smart stimulus-responsive ones, focusing on the construction of a rigid environment to suppress nonradiative deactivation by abundant inter/intramolecular interactions. The typical interactions in RTP polymer systems mainly include hydrogen bonding, ionic bonding, andcovalent bonding, which can change the molecular electronic structures and affect the energy dissipation channels of the excitedstates. An in-depth understanding of intrinsic mechanisms and an extensive exploration of potential applications for excitation-dependent color-tunable, ultraviolet (UV) irradiation-activated, temperature-dependent, water-responsive, and circularly polarizedRTP polymer systems are distinctly illustrated in this Account. Furthermore, we propose some detailed perspectives in terms ofmaterials design, mechanism exploration, and promising application potential with the hope to provide helpful guidance for thefuture development of amorphous organic RTP polymers.

Automated summary

Long-lived organic room-temperature phosphorescence materials have great potential applications in various fields. Compared to traditional fluorescence, phosphorescence originates from slow radiative transitions of triplet excitons. Enhancing intersystem crossing rate and suppressing nonradiative relaxation channels can achieve efficient phosphorescence in purely organic materials. Amorphous organic polymers offer improved processability and flexibility, making them more competitive for achieving long-lived phosphorescence emission.