Host-guest Intelligent-responsive Luminescent Materials And The Tuning Of Their Excited States

Intelligent-responsive luminescent materials are usually based on external field effects,i.e.,the structures of the materials can be changed under appropriate physical(such as optical,electrical,force,thermal,magnetic)and chemical(such as pH,ion concentration,gas,biomolecule)conditions,thereby achieving the modulation of optical properties(such as strength,lifetime,quantum yield,etc.).This kind of materials has attracted wide attention due to their sensitive response signal and good reversibility,which have broad applications in the field of intelligent switching and sensing.Currently,the design of new intelligent-responsive materials requires consideration of the following factors:(1)the practical application of materials requires fast response times and high visual contrast;(2)relative to a disordered powder or solution state,the preparation of the illuminating material into an ordered solid film will facilitate its use in smart devices and luminescence sensors.(3)For molecule-based luminescent materials,to achieve high photothermal stability and repeatability is a prerequisite for future large-scale applications.Constructing the host-guest structure is an effective way to improve the performance of intelligent-responsive luminescent materials.The rigid host matrix can be selected to fix the guest molecules into ordered system,which can effectively reduce the energy loss caused by the vibration/rotation of the guest molecules,and also avoid the luminescence quenching caused by the aggregation between the guest molecules.Layered double hydroxides(LDHs)have a typical rigid layer structure.Due to the strippability of the positively charged rigid laminates and the exchangeability of interlayer anions,orderly immobilization and functional integration within the host-guest materials can be achieved.Therefore,LDHs have shown fruitful application prospects in the fields of detection,anti-counterfeiting and biological treatment.In this paper,based on the intelligent-response luminescent properties of the host-guest materials,the LDHs and polymers are selected as the host,and the organic small molecules,metal complexes and anionic luminescent polymers are used as guest molecules.The object is to achieve intelligent-responsive performance into fluorescent/phosphorscent powder and film materials.Also,the regulation and optimization of structure and performance can be realized.The specific research contents are as follows:1.Study on the construction and performance of the host-guest intelligent-response fluorescent filmsThe LDHs with rigid laminates were selected as the host materials.The ordered and controlled immobilization of single/multiple fluorescent guest molecules were achieved by regulating the types of guest species(organic small molecules,complexes,etc.).Intelligent-responsive luminescent films with characteristics such as two-color polarized emission,angle-dependent luminescence,and two-photon up-conversion were obtained.The constructed fluorescent films have selective luminescent responses to external stimuli(humidity,temperature,and explosive compounds).Moreover,a universal method for constructing spatially-confined intelligent response materials has been developed.2.Construction and properties of host-guest room temperature phosphorescent(RTP)hybrid nanosheetsCarboxylate molecules were intercalated into the layer of the LDHs,and host-guest RTP hybrid materials were constructed.Based on the confinement effect of LDHs,the effective regulation of the excited states of interlayer molecules is achieved,and the triplet RTP lifetime is enhanced by more than 200 times.Theoretical calculations show that the RTP characteristics are related to the ordered arrangement of guest molecules between the LDHs layers and the formation of H aggregates.The constructed host-guest hybrid nanosheets present up-conversion phosphorescence and reversible temperature-responsive phosphorescence characteristics.Based on the co-intercalation of the donor-acceptor molecules,we have further developed a highly efficient phosphorescent energy transfer system(up to 99%energy transfer efficiency)by modulating the ratio of the donor to acceptor.The two-photon upconversion phosphorescence of host-guest hybrid nanosheets makes it a photosensitizer upon near-infrared light excitation.Long-lived triplet excitons were obtained by using the two-dimensional confinement effect of LDHs to achieve effective two-photon photodynamic therapy(PDT).Experiments have shown that the singlet oxygen yield of this nanocomposite is as high as 74%.In vitro cell experiments confirmed that it has a good anti-tumor effect with a median lethal dose of 0.153 ?g/mL.Compared with the traditional energy transfer-based two-component system,this work achieves a single photosensitizer for singlet oxygen generation and good PDT,providing new ideas for effective use of long-lived triplet excitons.3.Study on the construction and properties of RTP thin filmsWe have prepared self-supporting thin films by a hydrogen-bonding layer-by-layer method.Such RTP thin films have significant long-lasting luminescence properties,which can be identifiable by the naked eye on a time-resolved scale.And the research scope of the light-emitting films in the host-guest systems is expanded.In summary,by taking advantanges of experimental and theoretical studies,this thesis explored the relationship between the structures and properties of the host-guest materials;the single-and/or triple-state excited states of the host-guest luminescent materials are also tuned;the new host-guest fluorescent and phosphorescent materials with intelligent-responsive performances are further developed.