Design And Synthesis Of Novel Conjugated Organic Luminescent Materials And Their Multi-stimulus-responsive Behaviors

Conjugated organic molecules have delocalizedπelectrons,and the excited states stimulated by external field energy undergo radiation degeneration,which can show a variety of photoelectric response properties.Electrical,optical,thermal and mechanical stimuli are common excitation modes.Under different external field stimuli,conjugated organic molecules with different compositions and structures produce a variety of response behaviors,such as photoluminescence,mechanoluminescence,electro-luminescence,photovoltage,field effect,thermoelectric and piezoelectric phenomena etc.There are many important practical and potential applications in modern high-tech fields such as display lighting,biosensor,medical imaging,information recording/storage,optical encryption and anti-counterfeiting based on these unique stimulus-responsive behaviors.The macroscopic nature is the reflection of the microstructure.The study of various stimulus-responsive behaviors of different conjugated organic materials is not only helpful to understand the relationship between the structures and properties,but also has important guiding significance for the development of more functional and better performance stimulus-responsive materials.Recently,pure organic mechanoluminescence,mechanochromism and photo-phosphorescence materials have been widely inveatigated by the scientific researchers.However,the materials with excellent properties still have not been designed.In addition,the luminescence mechanism is still unclear now.Because different material systems with distinct chemical structures may exhibit different stimulus-responsive behaviors and mechanisms,in this dissertation,three kinds of conjugated organic molecular systems were designed and synthesized.In addition,mechanoluminescence,mechanochromism and photo-phosphorescence behaviors,which is stimulated by light and mechanical force,were investigated.Based on the crystal structure analysis and quantum chemical calculation and the investigation of a variety of stimulus-responsive materials,a series of novel conjugated organic luminescent materials with excellent performance were developed.The specific research contents and results are subrised as follows:1.Tripyridine derivatives are mostly used in the design and synthesis of functional organometallic complexes.Due to pure organic tripyridine derivatives with polynitrogen heterocyclic,it is potential to develop mechanoluminescence,mechanochromism and photo-phosphorescence behaviors.Howerver,to the best of our knowledge,there is no any articles to report this.In this dissertation,8 tripyridine derivatives substituted by different halogen and polar groups were designed and synthesized.It was found that Br-TPY and I-TPY with heveay-halogen bromophenyl and iodophenyl were endowed with fluorescence-phosphorescence dual emission phenomanon.The phosphorescence efficiency of Br-TPY is as high as 18.7%,except that I-TPY also shows a unique photo-stimulated reversible crystal and luminescence transformation behaviors.The piezochromism behavior of organic crystals with dual emission proporty under hydrostatic pressure was first time studied.It’s found that the fluorescence and phosphorescence intensity and spectral red-shift distance of Br-TPY showed obvious asynchronous changes.The theoretical calculation results show that under static high pressure the volume of the crystal will be contracted,which will result in the level of singlet energy level decrease much more than that of triplet state.In addition,phenyl tripyridine with substituted with pinacol borate and formamide showed bright mechano-luminescence.The strong polar and polyatomic amide phenyl tripyridine enhanced intersystem channeling and intermolecular interaction particularly,which make the photophosphorescence lifetime much higher than that of other tripyridine derivatives.Furthermore,it’s also showing a rare phenomenon of force-induced fluorescence-phosphorescence dual emission and white light emission.2.Carbazole is a kind of room temperature phosphorescence（RTP）material and shows visible mechanoluminescence to the naked eye.It has been reported that based on carbazole,some RTP materials with different substituents have been designed and synthesized.In this dissertation,the mechanoluminescence properties of phenylcarbazole（NPC）and its application in the multicolor mechanoluminescence materials have been studied for the first time.Three isomers（NPC-oCN,NPC-mCN and NPC-pCN）with o-,m-and p-substituents on NPC N-benzene ring were designed and synthesized,and the room temperature phosphorescence properties of these isomers were studied.Unexpectly,it’s found that NPC crystals show touch-sensitive mechanoluminescence properties,which is related to piezoelectric space group properties and 3D supramolecular hydrogen bond network by assembled.Due to the NPC with the low melting point and easy crystallinity,multicolor mechanoluminescence materials can be obtained by melt doping of various organic phosphors,which provides an effective new pathway to expand the range of mechanoluminescence spectra simply and conveniently.Furthermore,through the study of room temperature phosphorescence propertie of cyanophenylcarbazole isomers,it’s found that isomerization can regulate crystal stacking modes,intermolecular interaction and intersystem channeling probability,which provides an effective means for the research and optimization of RTP materials.NPC-pCN has bright and long life room temperature phosphorescence properties,and this phosphorescence property is almost unchanged upon heavy grinding.Based on this theory and experiment result,PMMA/NPC-pCN blends with excellent processability and room temperature phosphorescence properties were investigated,and the relationship between their structure and properties was analyzed.It is found that the doped polymer has unique concentration-dependent phosphorescence color,phosphorescence recording and memory functions.And its resolution is up to hundreds of meshes and memory founction by UV irradiation is lasting for more than 15 hours.It has provided a new pathway for the universal application of organic small molecule room temperature phosphorescence（RTP）materials.3.9,10-diphenyl anthracene has a large internal rotation barrier,and the introduction of new functional groups in the adjacent position of benzene ring can further increase the steric hindrance,which may effectively prevent the aromatic ring from rotating across the plane and form two stable conformational isomers.Based on this idea,9,10-bis（2-aldehyde-phenyl）anthracene（An-Ph-CHO）and 9,10-bis（2,5-dimethylphenyl）anthracene（An-Ph-4CH₃）were designed and synthesized.Two conformational isomers of An-Ph-CHO were successfully separated and characterized for the first time,and anthracene central cyclotron cross-conformational isomers with designated conformation of diphenyloxadiazole or diphenylethylene were prepared.Preliminary studies show that they have different aggregation structures and mechanoluminescence properties.From An-Ph-4CH₃,anthracene central cyclotron cross-conjugated molecule（An-O-CH₃）with diphenylvinylbenzene as branching was obtained.It’s found that it’s a mixture of cis-and trans-conformational isomers.However,the reversible transformation and separation of conformational isomers can be achieved by heating.Theoretical calculations show that the transition of cyclotron conformational isomers is accompanied simultaneously by the transition of anthracene-plane folded-configuration.It is found that only syn-An-O-CH₃has strong mechanoluminescence property,which may be related to the crystalline piezoelectric properties.