Synthesis And Circularly Polarized Luminescence Performance Study Of Chiral Metal-Organic Framework-Luminophor Composites

With the continued development of society,people’s demand for advanced intelligent optical equipment is increasing.Among these,chiroptical activity,including circular dichroicity and circularly polarized light,especially circularly polarized light,provides an opportunity for this.In recent years,due to its unique polarization,potential applications in 3D display,optical information storage or encryption,optical sensing,etc.,have been widely studied.Traditionally,circularly polarized light is produced by a quarter-wave plate,but during this process,the loss of light energy is inevitable.The circularly polarized light can be produced directly from the chiral luminescent material in the form of circularly polarized luminescence（CPL）,which prevents the energy loss caused by the conventional method.Therefore,researching CPL materials has received increasing attentions from researchers around the world.A typical method of preparing CPL active materials is to covalently attach the chiral moieties to luminophores.Using the method,researchers have successfully synthesized various CPL materials,such as chiral organic molecules,chiral metal complexes,and so on.However,the CPL signs of the obtained chiral material are unpredictable,and the cumbersome redundant synthetic procedures are also inevitable.In order to cope with these challenges,the host-guest method of combining the chiral host with the achiral luminescent guests has become an emerging research hotspot in recent years.However,in most reported references,CPL properties were measured in a mobile phase.This greatly hinders the development and application of CPL active solid state materials.Based on the above research background,this thesis focuses on designable chiral space of the chiral metal organic frameworks（CFOMs）.In addition,from the structural design and selection of the CMOF host,it explores effective chiral space-confined achiral luminescent guests,and studies the general route of a chiral MOF host inducing luminescent guest to produce adjustable CPL,the key role of a chiral MOF in this process and the interaction between host and guest,and the CPL characteristics and potential applications of CMOF-luminophore composites.The main research is divided into the following three aspects:1.By using a pair of enantiomeric CMOFs with nanometer-sized helical channels as the host to confine a variety of achiral fluorescent dyes（guests）with different luminescences,CPL CMOF-dyes composites with customizable emission light were prepared by an in-situ synthesis method,and white CPL crystalline composites with high quantum yields were also fabricated by adjusting the ratio of different achiral dyes.Subsequently,detailed spectroscopic characterizations and theoretical computational analysis studies were carried out.The achiral fluorescent molecules are confined in the helical channels of the enantiomeric L/D-CMOF,effectively overcoming the aggregation-induced quenching effect.In addition,they attach to the inner surface of the helical channel via hydrogen bonding and inherit the helicality of channel,leading to their tendency to helically align in the helical channel,thereby generating chiroptical activity.The g_lum of this series of CMOF-dyes follows the trend of the host-guset interaction energy,where the maximum glum is±0.0115.In addition,WCPLED was assembled with the synthesized white CPL crystalline composites.This work shows for the first time that the helical channels of chiral MOFs can be used as a universal template to prepare CPL-active solid-state materials with high quantum yields and ideal glum.2.Through a two-step self-assembly method of chiral rare-earth CMOFs（（P）-（+）/（M）-（-）-EuMOF）and perovskite nanocrystals MAPbX₃（MA=CH₃NH₃⁺,X=Cl^-,Br^-,I^-）,we prepared three pairs of crystalline enantiomeric adducts for the first time.Among them,the achiral MAPbBr₃ NCs embedded into chiral MOFs inherit the chirality of the host CMOFs through the Eu-Br and Pb-O coordination bonds between the host and guest,which has been demonstrated by synchrotron X-ray absorption spectroscopy.The composites show enhanced photoluminescence quantum yields（PLQY）and good thermal stability of CPL in air,and photoswitchable CPL properties upon altering different UV irradiation.Based on the two chiral emission centers of（P）-（+）/（M）-（-）-EuMOF（?）MAPb Br₃ and their different properties,we have achieved reversible CPL switching under external stimuli,e.g.,chemical reagents（deionized water/MABr solution）or temperature（room temperature/high temperature）,also systematically investigated multiple information encoding,encryption and decryption applications,and successfully established a novel chiral integrated combinatorial logic gate.This work opens a new way to prepare solid-state CPL composites and develops new applications based on switchable CPL.3.Based on the host-guest induction methods proposed in the above work,we innovatively propose to use a CMOF（L/D-CZIF）as the host to encapsulate the guest metal clusters（AuNCs and AgNCs）and thus endow them CPL.First,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,high-resolution X-ray photoelectron spectroscopy（XPS）and optical characterization together demonstrate that AuNCs and AgNCs are embedded in CMOFs.Impressively,such a strategy not only improves photoluminescence quantum yield of the clusters,but also imparts circularly polarized luminescence to the AuNCs and AgNCs.The quantum yields of Au NCs and AgNCs increased from 0.2%and 2%in the solution state to 15%and 7%in the embedded into L/D-CZIF state,respectively.During the in-situ formation of CMOF-cluster composites,the chiral hosts（L/D-CZIF）provide chiral microenvironments that may induce the chiroptical properties of the clusters through chiral perturbation.This work sheds some light on the design of metal clusters with chiroptical activity.