Design,Synthesis And Photoelectric Properties Of Iridium(Ⅲ) Complexes Based On Difluorophenylpyrazole Cyclometalated Ligand

In recent years,iridium（Ⅲ） complexes have been successfully applied to organic optoelectronic devices,biological imaging,sensing and information storage due to their excellent photophysical properties,including ligand-adjustable luminescence color,short excited state lifetime,high luminescence quantum efficiency,good photothermal and electrochemical stability.However,at present,iridium（Ⅲ）complexes still face some problems that will restrict their further application,and the unique luminescence behaviors have rarely been reported.So far,researchers have reported a series of strategies to optimize the performance of iridium（Ⅲ）complexes.（1）The introduction of groups with steric hindrance on the ligand to increase the distance between the two molecules in the aggregated state to effectively solve the concentration quenching problem.（2）Building supramolecular cages or introducing intramolecularπ–πstacking interactions to improve the stability of the device.Therefore,continuing the rational design and synthesis of new iridium（Ⅲ）complexes,understanding the relationship between their structure and properties,achieving the modulation of luminescence properties through simple methods,and obtaining iridium（Ⅲ）complexes with unique luminescence properties will enrich the whole materials system and improve its further development and application.In this paper,we used 1-（2,4-difluorophenyl）-1H-pyrazole as the cyclometalated ligands,modified different ancillary ligands by different methods to obtain a series of new cationic iridium（Ⅲ）complexes,and conducted detailed studies on their photophysical properties to understand the relationship between their structure and properties,the main research contents are as follows:（1）Using flexible chains as bridging units,two flexible iridium（Ⅲ）complexes[Ir1-f][PF₆]and[Ir2-f][2PF₆]with different counterion numbers were designed and synthesized,which exhibited AIE and ACQ characteristics,respectively.Theoretical calculations support that the different luminescence behavior may arise from different excited state properties in solution.Furthermore,experimental results suggest that excessive intermolecular interactions are also responsible for the luminescence quenching of complex[Ir2-f][2PF₆]in the solid state due to the introduction of additional counterions.Finally,the complex[Ir1-f][PF₆]was successfully applied to security and bioimaging based on its unique AIE and MCL properties.（2）Continuing from the counterion perspective,a series of iridium（Ⅲ）complexes Ir-2NMe,Ir-2NPh,Ir-3NMe and Ir-3NPh with AIE properties were designed and synthesized by utilizing ancillary ligands with different rotational units and rich aromaticπsystems to construct anion–πinteractions to alleviate unfavorableπ–πstacking.Theoretical calculations and experimental measures were performed to elucidate the anion–πinteractions as the main reason for the AIE phenomenon in the materials.Finally,an anti-counterfeiting application based on the complex Ir-3NPh was successfully prepared.（3）A set of mono-and dinuclear iridium（Ⅲ）complexes M-Ir1 and D-Ir2 have been designed and synthesized by constructing ancillary ligands with different numbers of chelation sites using the benzene ring as a bridging unit,and the conformational relationships have been understood by combining experiments with theoretical calculations.Due to the introduction of additional metal centers,the dinuclear complex D-Ir2 possesses more intersystem crossing paths and higher stability.Finally,the two materials were successfully applied to LECs devices and better device performance was obtained in D-Ir2-based flexible LECs with current efficiency,external quantum efficiency and lifetime of 14.2 cd A^-1,5.1%and 312 min,respectively.（4）Continuing with the benzene ring as the bridging unit,two rigid iridium（Ⅲ）complexes[Ir1-r][PF₆]and[Ir2-r][2PF₆]with different counterion numbers were designed and synthesized.The introduction of the benzene ring increases the molecular rigidity and further optimizes the intermolecular interactions,and both complexes exhibit significant AIE and MCL behaviors.Interestingly,the complex[Ir2-r][2PF₆]also exhibits unique photo-induced and pressure-induced luminescence enhancement behaviors,and excellent luminescence behavior could been retained to ambient conditions upon decompression.The unique luminescence phenomena of the materials are explained by experimental means and theoretical simulations as the presence of multiple intermolecular interactions.Finally,the materials were successfully applied to information storage.