Preparation And Properties Of High Luminance Solid-state Luminescent Molecules Based On Benzothiadiazole Or Benzimidazole Units

Organic light-emitting materials have been regarded as one of the most critical materials in various applicaions,such as fluorescent coatings,fluorescent brighteners,dye lasers,bioanalytical light-emitting probes,color-changing light-emitting devices,organic light-emitting devices,etc.The development of efficient fluorescent materials is not only important for basic research,but also for practical applications.At the same time,formochromic smart materials that show emission changes after exposure to external mechanical stimuli have attracted wide attention due to their appli3 ion prospects in fluorescence switches and sensors.At present,the effective appli3 ion of photoluminescent materials is hampered by two main factors.1)Most of the photoluminescent materials do not exhibit high contrast photoluminescence changes with large color difference.2)The fluorescent bands of most of these materials before and after grinding are lo3 ed in the visible region,resulting in poor penetration.In general,efficient solid-state emission is essential for achieving significant mechanical fluorescence discoloration.However,traditional fluorescent molecules can undergo aggregation-induced quenching(ACQ)when doped into inorganic nanomaterials.Aggregation-induced emission(AIE)is an unusual and interesting fluorescence phenomenon that is attracting increasing interest for applications in biomedical imaging,chemical sensors,and light-emitting diodes(LED).Compared with conventional organic dyes,AIE active molecules fluoresce more intensely in their aggregated or solid states.It provides a way to overcome the shortcomings of conventional organic molecules.They have been carefully designed and their structure adjusted by introducing some functional groups and subunits.Over the past few decades,the preparation and surface modificaion of various organic luminescent materials doped with AIE active molecules have been reported.The strong electron acceptance properties of the benzothiadiazole(BTD)core are usually used in the design and synthesis of the donor-(π)-acceptor structure(D-(π)-A molecular structure or push-pull chromophore).The π spacer in the D-A structure has an effect on the π conjugated,and therefore on the optical properties of fluorescent BTD compounds.But in principle it is not necessary for stable intramolecular charge transfer(ICT)in excited states.Icts are usually observed from the donor part to the BTD core.Although sometimes it is not necessary,π spacers may help improve charge separation and reduce the band gap value of the fluorescence structure.Many thiadiazole derivatives can achieve long wavelength emission through reasonable structural modificaion,so they are widely used as components of efficient solid-state luminescent materials.Inspired by relevant studies,this thesis is aimed at designing highly solid luminescent organic material molecules from benzothiadiazole unit.The design,synthesis and research system of this paper is as follows:1.Fluorescence molecules Ⅰ-1,Ⅰ-2,Ⅰ-3,Ⅰ-4,benzothiadiazole,dibenzobenzimidazole and trianiline groups as the core skeleton,introduced different degrees of distortion of molecular units for regulation.The properties of these fluorescent molecules showed that they exhibited remarkable aggregation-induced emission characteristics,with high brightness of crimson aggregative fluorescence.These highly emittance fluorophores exhibit different photoluminescence in the solid state,including two fluorescent colors: orange and crimson.In addition,these fluorescent molecules also exhibit different mechanical response emission characteristics.The orange emitting triplet compounds containing dibenzobenzimidazole,benzothiadiazole and trianiline units showed deep red fluorescence after mechanical grinding.Therefore,the dye has high contrast mechanical discoloration properties.In contrast,the other three crimson fluorescent compounds showed no significant emission changes after grinding.2.Compounds Ⅱ-1,Ⅱ-2,and Ⅱ-3 were successfully prepared by a simple coupling reaction.By introducing units with different conjugation degrees,the two sides of benzothiadiazole were fine-tuned.The properties of compound Ⅱ-1 in solid state showed no significant emission change after grinding.Compound Ⅱ-2 and compound Ⅱ-3 exhibit rare blue-shift force chromotropic properties.3.Nine fluorescent molecules Ⅲ-1～Ⅲ-9 based on benzimidazole and benzothiadiazole units were designed and prepared.Fluorescence emission(PL)spectra and X-ray diffraction(XRD)were used to study the luminescence behavior of molecules Ⅲ-1～Ⅲ-9 in high solid state.The study says: In solid state,compounds Ⅲ-1 and Ⅲ-2 showed blue shift and force shift,while Ⅲ-3～Ⅲ-9 showed red shift,where Ⅲ-3,Ⅲ-4,Ⅲ-6,Ⅲ-7,Ⅲ-8 and Ⅲ-9 were ground and left at room temperature for two minutes.The emission peaks show different degree of recovery.