Cyclization Boosted Long-Lived Polymeric Phosphorescence under Ambient Conditions

Room-temperature phosphorescence (RTP) is a fascinating optical phenomenon, and a variety of methods have been developed to achieve and improve the desirable phosphorescent performance on demand. Cyclization of the molecular structure is an efficient strategy to promote phosphorescence at 77 K by boosting intersystem crossing (ISC). However, cyclization-triggered phosphorescence at room temperature has not yet been reported, especially for polymer systems. Herein, we proposed and demonstrated a concise yet efficient strategy to obtain ultralong phosphorescence under room temperature by the cyclization of the polymer chain, in which the carboxyl and cyano groups are rearranged and isomerized to generate an imide ring at high temperatures. In this work, the phosphorescent performance of materials is greatly advanced. Interestingly, cyclized phosphorescence lifetime and phosphorescence quantum yield have been increased by 17 times (51.4–914.0 ms) and 9 times (1.5–14.0%), respectively, compared to linear polymers. The reason for promoting phosphorescence was that the cyclization of the polymer chain dramatically increased the ISC channel, which was accompanied by the rigid structure of the system, leading to satisfactory phosphorescence efficiency at room temperature. This strategy may provide a new idea for the preparation of ultralong RTP materials by enhancing ISC and rigidification.