Study On Aggregation-induced Luminescence And Solid-state Fluorescence Conversion Of Fluorene And Fluorenone Compounds

Recently,Organic fluorescent materials have attracted wide attention in the field of photochemical research and optoelectronic devices,especially fluorescent materials with stimulating response.Since many of the practical applications of organic fluorescent materials must be in solid or thin film state,a high fluorescence quantum yield is required for the compound in the aggregation state.Traditional organic compounds has a high fluorescence efficiency in dilute solution,while fluorescence is drastically weakened or even directly quenched in aggregated states,which is mainly resulted from the phenomenon of aggregation induced quenching.Many researchers initially prevent from the quenching by some chemical or physical methods,eventually it cannot meet with the ideal results.The discovery of aggregation induced luminescence(AIE)phenomenon provides a new idea for the design and synthesis of solid-state fluorescent materials.In recent years,the developed organic solid fluorescent materials of stimulated-response type show a very large potential use in the field of information storage,security,security ink and other fields.Previous studies have shown that fluorenone molecules exhibit excellent properties in AIE and fluorescence conversion of stimulated-response.In this paper,the structures of the fluorenone units are improved and expanded based on the previous research,and a series of novel AIE molecules and solid fluorescence conversion molecules of stimulated-response are designed and synthesized.And the AIE mechanism and its relationship between structure and performance are emphatically studied,and the following innovative results are achieved:1.Four aryl-substituted fluorenone compounds are designed and synthesized,respectively,DPF,PDOF,DDOF and NDOF,which have typical AIE properties and have higher fluorescence quantum yields.With the increasing of fluorescence intensity,a red shift of about 160 nm is accompanied.The mechanism of AIE is revealed by analyzing single crystal structure and theoretical calculation.In the X-ray crystallographic packing,it is found that a dimer is formed by every two molecules through hydrogen bonds,then an excimer is formed after being excited.It is believed that the red-shift phenomenon is derived from the excimer.In addition,the spectral characteristics show that the compounds,PDOF,DDOF and NDOF,are easier to form excimer than DPF.2.Four symmetric and asymmetric thiophene-substituted fluorenone derivatives,respectively,CTPF,ATPF,BTPF and ETPF are designed and synthesized,which all have high fluorescence quantum yields and typical AIE properties.The molecular aggregation process not only enhances the fluorescence emission peak,but also makes a redshift of 170 nm with respect to their single molecule emission peaks.The single crystal structure show that the two adjacent molecules form a static excimer by ?-? interaction,and it is believed that the red-shift phenomenon mainly comes from the formation of static excimers.In addition,the molecular orbital energy of single molecule ATPF and ATPF dimer are calculated,and the calculated results are in agreement with the absorption spectra and emission spectra.3.The fluorene compound MDPFare synthesized,which exhibits high luminous efficiency both in solution and in solid conditions.The single crystals are cultured by solvent evaporation method and solvent stratification method,and three single crystals,G-MDPF,B-MDPF and V-MDPF,with different fluorescence emission are finally obtained,in which the blue B-MDPF can be turned into purple by heating,while the yellow G-MDPF can be turned into blue by heating.It can been known from XRD that the mutual discoloration process is the transition between crystal phase and crystal phase.In order to explore the mechanism of fluorescence conversion,single crystal structures are resolved.It can been known that single crystals with different colors are different in the accumulation modes,and charge transfer pathways under different excitations exist,resulting in different fluorescent colors.