New progress in the field of circular polarization luminescence in self-assembly systems
Switching and inversion of the handedness and circularly polarized luminescence (CPL) in chiral supramolecular system has attracted great interests, not only for their potential applications in the construction of chiroptical materials, but also for their unique roles in understanding the chirality-switching and circularly polarized bioluminescence mechanism observed in nature. A major challenge in this field is to use tunable supramolecular system based on a single enantiomer of assembly unit, to selectively obtain left-handed or right-handed CPL depending on the type and sequence of external trigger signals, which is appealing to fabricate smart chiral supramolecular materials.
Recently, Professor LIU Minghua from Institute of Chemistry, Chinese Academy of Sciences reported a novel strategy that coordination-driven pyrene-Histidine supramolecular system to achieve the switchable reversal of supramolecular chirality and circularly polarized fluorescent signals in different assembly pathways. By using Zn(II) coordinated with imidazole groups, the nanofiber structures changed into nanospheres and gave reversed chirality as well as CPL. The coordination interaction changed the chromophore packing model from T-shaped stacking to parallel п-п stacking. Noticeably, the reversible inversion of supramolecular chirality could be repeated for several cycles by adding complementary external stimuli in turns. Collective characterization with extensive spectra data coupled with X-ray crystallographic analysis and DFT calculations revealed that the change of pi stacking modes between T-shaped and п-п stacking was responsible for these switching phenomena. This work provided not only a deep insight into how coordination and pi-stacking modes could affect supramolecular chirality as well as their excited states chirality in chiral assemblies, but also a new way for developing switchable chiroptical supramolecular materials.
Their work entitled “Self-Assembly through Coordination and p-Stacking:Controlled Switching of Circularly Polarized Luminescence” has been published in Angew. Chem. Int. Ed. 2019, 58, 5946-5950.
Illustration of inversion and switching of CPL regulated by coordination and π-stacking. (Image by Prof. LIU Minghua)
Prof. LIU Minghua
Institute of Chemistry, Chinese Academy of Sciences