Organic room temperature persistent luminescence (ORTPL) is the phenomenon that materials can still exhibit persistent luminescence visible by bare eyes after removal of external excitation sources. Such characteristic is quite common in nature with inorganic materials but extremely rare in organic systems, which have only become the trending research focus in the last few years. These materials can be utilized in bio-sensing, information encryption and organic light emitting applications, etc. However, it remains a big challenge to design ORTPL materials with simultaneously high phosphorescence efficiency and long triplet lifetime. Meanwhile, materials with circular polarized luminescence (CPL) have been proven intriguing and quite valuable in applications such as 3D display, information encryption and storage as well as asymmetric photo-catalysis, etc. The combination of CPL and ORTPL is quite unique and promising but the several reported cases often came with low g index values, which corresponds to the capability and extent of CPL (normally the larger, the better).
Herein, Prof. You-Xuan Zheng’s group reported the first OPRTP materials based on paracyclophane. The afterglow of these materials can last for several seconds after removal of external excitation source under ambient conditions. The intrinsic large steric hindrance can help prohibit the intermolecular π…π stacking and interactions, facilitating the room temperature phosphorescence through inhibition of non-radiative decay processes. In addition, the triplet lifetime can be enhanced from less than 0.1 s to more than 0.5 s through two distinguished strategies, which opens new feasible pathways towards the design of OPRTP species.
Based on previous endeavors on CPL materials and devices (Chem. Eur. J. 2019, 25, 5672; J. Mater. Chem. C, 2019, 7, 7045-7052; Adv. Mater. 2019, 1900524) in Prof. You-Xuan Zheng’s group, the introduction of paracyclophane can help endow the materials with both ORTPL and CPL capabilities, with the highest g value of -1.2×10-2, which is among the best in this criterion. Both the racemate and enantiomers exhibit similar excellent OPTPL characteristics, making them potentially applicable in bio-systems, information encryption, etc.
This work was published in Angew. Chemie. Int. Ed.(2019, 58, 17220 –17225) with the title “Organic Room Temperature Phosphorescence with Strong Circular Polarized Luminescence based on Paracyclophanes”. PhD candidate Xiao Liang is the first author and master degree candidate Tingting Liu is the second author. Special thanks to Prof. Jing-Lin Zuo and Prof. Yi Wang for their kind help and support during the work. This work is also financially supported by National Natural Science Foundation of China (51773088).