Design of innovative experimental training on the effect of substitution position on properties of tetraphenyl-imidazole isomers
[Objective]Isomers have gained increasing attention from researchers across the world mainly due to their widespread applications in medicinal,materials sciences,and optoelectronics fields.Isomers with the same atomic bond structure but different geometrical atomic positions in space do not always possess similar properties,even if they have the same functional groups.Thus,they can be utilized as model compounds to investigate the relationship between the structure and its properties,facilitating the development of functional materials.However,the research on the structural-property relationships of isomers has not been integrated into undergraduate experimental teaching.As a result,students'understanding of isomers is largely confined to a perceptual cognition level.To facilitate a visual comprehension of the core chemical principle governing the structural properties,foster the integration of research and teaching,and broaden pathways for cultivating high-caliber talents,an innovative experiment was designed based on the previous research achievements in isomers.[Methods]In this experiment,the para-and meta-linked tetraphenylethylene-imidazole isomers,TPEBM and TPEmBM,were synthesized based on a two-step reaction involving the condensation cyclization of amine aldehyde and the Buchwald-Hartwig C-N coupling.The isomers exhibit aggregation-induced emission(AIE)properties,which are characterized by weak fluorescence in dilute solutions but significantly enhanced fluorescence in the aggregated state,a topic that has been increasingly studied by researchers across the world.The structures of the isomers were evaluated using nuclear magnetic resonance(NMR),high-resolution mass spectrometry(HRMS),and single-crystal X-ray diffraction analysis.The optoelectronic properties were assessed using instruments such as UV-Vis spectrophotometers,fluorescence spectrophotometers,differential scanning calorimeters,and electrochemical workstations.The differences in the properties of the isomers were analyzed,and Gaussian theoretical calculations were employed to explore the underlying reasons for these variations.Finally,OLED devices integrating the synthesized materials were fabricated to investigate their potential applications.[Results]The aforementioned research has demonstrated that even a subtle difference in the meta and para linkages may lead to significant alterations in the properties of the compounds.Compared to the meta-linked TPEmBM,the para-linked TPEBM exhibits a noticeable red shift in UV and fluorescence spectra.The solid-state absolute fluorescence quantum yield of the meta compound TPEmBM(80.98% )is significantly higher than that of the para compound TPEBM(31.80% ).The AIE performances of the two compounds also varied significantly.In a THF/water mixed solution,as the water content gradually increases,the fluorescence intensity of para-TPEBM enhances while the meta-TPEmBM initially enhances,followed by weakening before re-enhancing again.Furthermore,meta-TPEmBM exhibits distinct mechanochromic behavior,wherein the application of external force induces a fluorescence transition from blue to green;conversely,no such phenomenon was observed for para-TPEBM.The differences in properties may be attributed to the enhanced conjugation observed in the para-linked structure,while the meta-linkage induces a more distorted molecular configuration,resulting in distinct aggregation states across diverse environments.[Conclusions]This experiment is highly comprehensive and rich in content,and it encompasses a complete research process of"material design and synthesis―structural characterization―related property testing and analysis―theoretical calculation―optoelectronic performance testing and evaluation."Based on such comprehensive and systematic innovative training,students have acquired proficiency in experimental techniques such as extraction,column chromatography and recrystallization,learned to use various precision instruments and mastered relevant data analysis methods.Furthermore,they have gained an intuitive understanding of the intricate relationship between the molecular structure and its properties.The innovative experiment not only enhances students'scientific innovative thinking and scientific exploration abilities,which enhances their ability to analyze and resolve problems but also provides valuable practical experience to promote in-depth research in the field of chemistry.In addition to this,integrating this research in teaching can effectively improve the quality of experimental teaching,laying a solid foundation for cultivating high-quality top-tier talents and offering robust support for the innovative development of chemical education.
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