Lighting Up Rotaxanes with Tunable and Switchable Circularly Polarized Luminescence

Conspectus: As a typical class of mechanically interlocked molecules (MIMs), rotaxanes reveal unique interlocked structures, as well as controllable dynamic behaviors that originate from the mechanical bonds. Owing to such attractive structural and dynamic features, rotaxanes have proven to be not only privileged candidates for the construction of diverse artificial molecular machines such as molecular shuttles, molecular muscles, and molecular pumps but also versatile platforms for wide applications in sensing, drug delivery, and catalysis. In particular, aiming at the construction of novel rotaxanes with intriguing (chir)optical properties, the rapid development of luminescent rotaxanes, particularly ones with attractive circularly polarized luminescence (CPL), has been witnessed. On the one hand, the unique interlocked structures of rotaxanes enable the facile introduction of various luminogens into different components with well-defined and tunable chiral arrangements. This makes the resultant integrated luminescent rotaxanes not only attractive candidates for the development of novel CPL-active materials with desirable and tunable CPL performances but also promising platforms for investigations of structure–property relationships. On the other hand, the controllable dynamic features of rotaxanes could lead to the successful construction of novel smart chiral luminescent materials with precisely switchable CPL emission states, including the handedness, emission wavelength, photoluminescence quantum yield (PLQY), and dissymmetry factor (g_lum). This further extends their applications in diverse fields, such as smart devices and sensors. Considering all the above broad potential applications, the design and construction of novel CPL-active rotaxanes, particularly ones with tunable and switchable CPL performances, are of great importance.During recent years, through the rational design and synthesis of chiral rotaxanes with precisely arranged luminogens, we realized the successful synthesis of a series of CPL-active rotaxanes. We first confirmed the unique role of mechanical bonds in boosting the CPL performance of chiral pillar[5]arene wheels upon the formation of rotaxanes, highlighting that rotaxanes can serve as promising platforms for the design and construction of novel CPL emitters. Furthermore, through the rational design and synthesis of mechano-stereoisomers, including both static and dynamic ones, the precise tuning and switching of the CPL performances of diverse chiral rotaxanes were successfully realized. In addition to individual chiral rotaxanes, we also showed an interesting generation-dependent CPL performance of rotaxane-branched dendrimers with multiple chiral rotaxane units as branches and realized further enhancement of their CPL performances through sequential light harvesting. In this Account, we summarize our above exploration of rotaxanes with tunable and switchable CPL performances, and we hope that it will inspire scientists from various disciplines to explore these appealing and versatile platforms for wide applications.