Recent Advances of Pure Organic Room Temperature Phosphorescence Based on Functional Polymers

The phosphorescence is produced by the radiative transition of the excited triplet state which is generated by the intersystem crossing (ISC) from the excited singlet state. Compared with fluorescence, it has a longer luminescence lifetime and larger Stokes shift, so phosphorescent materials have great application value in fields such as displays, anticounterfeiting, and imaging. But due to the low ISC rate of organic molecules, the slow radiative transition rate of the triplet state, and the large nonradiative energy loss caused by molecular vibration, pure organic room temperature phosphorescence (RTP) is usually difficult to obtain. Among the most widely used strategies including crystal assembly, polymerization, and host-guest encapsulation, the polymerization strategy based on rigid polymers has achieved great success and widespread attention due to their easy processing and excellent luminescence performance.The main function of polymers is to fix the luminophore into the matrix and suppress the energy loss of the triplet state caused by nonradiative transitions and oxygen quenching. That is, polymers provide a rigid microenvironment necessary for the RTP, although some polymers are flexible and stretchable. Conventional polymers have limited interaction with luminophores and do not have the function of promoting triplet states. Therefore, the high RTP quantum yield depends more on the structural design of luminophores. By modification of the structure, functionalized polymers can be endowed with the ability to regulate the singlet and triplet energy levels of luminophores, enhance ISC, and increase the quantum yield of RTP. The selection of functionalized polymers also enriches the diverse properties of RTP materials.This Account summarizes the latest research progress in the field of polymer-based RTP and RTP enhancement by functionalized polymers. Luminophores are used to construct RTP systems by doping, covalent linking, or supramolecular interactions with polymers such as PAA, PMMA, PVA, and PAM. To further strengthen polymer rigidity, secondary processing has been successfully employed to synergistically suppress nonradioactivation and enhance RTP performance, such as hydrogen bonding bridges, host-guest encapsulation, and cross-linking. The function of polymers is no longer limited to suppressing nonradiative transitions but also includes enhancing the yield of triplet states and generating special luminescence phenomena. A few functionalized polymers are specially designed to utilize external heavy atom effects, dipole-dipole interactions, and electrostatic and diffusion interactions with the luminophores to promote the ISC rate. Due to the diversification and functionalization of polymers, RTP systems were developed with various special luminescence phenomena such as photoactivation, excitation wavelength dependence, photochromism, circularly polarized RTP, and stimulus-response. We hope the summarized functions and development trends of polymers in RTP systems can provide helpful guidance for designing more high-performance RTP materials.