Construction And Application Of Cationic Dinuclear Ir(?) Complexes With Aggregation-induced Emission And Piezochromic Luminescence Properties

Recently,piezochromic luminescence(PCL)materials exhibiting visible and reversible changes of luminescence in the solid state upon external pressure stimuli,have attracted extensive attention from researchers.These materials with high contrast are regarded as attractive alternatives for sensors,memory storage,and security inks etc.Transition metal Ir(?)complexes have been the subject of intensive topics owing to their good photo-thermal stability and easy tunability of emission colors.However,Ir(?)complexes are also faced with a seriously problem: aggregation-caused quenching(ACQ),which limits these materials in the field of PCL application.In 2001,Tang's group proposed an anti-ACQ phenomenon named aggregation-induced emission(AIE).This concept greatly overcomes unsatisfactory solid luminescence performances in Ir(?)complexes,broadening the way to search efficient solid-state luminescent materials.Additionally,compared with mononuclear Ir(?)complexes,cationic dinuclear Ir(?)complexes have more chances to introduce functional groups and can realize better photophysical properties.Until now,due to the lack of reasonable molecular design strategy,the exploration of structure-property correlations on cationic dinuclear Ir(?)complexes combined AIE and PCL behaviours has not been underdeveloped.On the other hand,cationic dinuclear Ir(?)complexes with both AIE and PCL properties are really scarce.Therefore,the study of rational design principle can be used to(i)synthesis cationic dinuclear Ir(?)complexes simultaneously exhibiting AIE active and brilliant PCL performance;(ii)assess the influence of chemical structure on their properties.Thus,an effective and comprehensive molecular design strategy is established.Based on this,more multifunctional PCL materials have been constructed.The development of new materials will enrich the scope of Ir(?)complexes and spark a rapid expansion in the field of solid intelligent luminous materials.In this paper,we designed and synthesized a series of functional cationic dinuclear Ir(?)complexes by utilizing appropriate ancillary ligands and easily tunable cyclometalated ligands.Acylhydrazone ancillary ligands simultaneously contain imine units(-C=N-)and amide bond(-CONH-),in which-C=N-could realize the AIE behaviour,while the-CONH-provides hydrogen-bonding sites for PCL.2-phenylpyridine and its derivatives are common cyclometalated ligands,which contribute to the diversity of Ir(?)complexes.The relative studies are outlined as follows:(1)Two novel cationic dinuclear Ir(?)complexes containing same acylhydrazone ancillary ligand(BPTH)were designed and synthesized.Both luminophores display remarkable AIE behaviors and high-contrast PCL characteristics.Detailed analyses of ~1H NMR spectra,powder X-ray diffraction(PXRD)and Fourier transform(FT-IR)spectra data indicate that PCL behaviors of the complexes result from the effective transition from crystalline to amorphous,and the transition of intermolecular hydrogen bonds from well-ordered arrangement to disordered arrangement.Notably,the strategy of introducing hydrogen bond sites into Ir(?)complexes provides a feasible way for designing “smart” PCL materials.Based on the PCL characteristics of complexes 1 and 2,the proof-of-concept data encryption and re-writable devices are fabricated,respectively.(2)Founded on the design strategy of our previous work,a new acylhydrazone ligand L1 was obtained by modifying the ligand BPTH with methyl group.The novel cationic dinuclear Ir(?)complex with AIE active,PCL property and solvent-driven luminescence was realized by introduction of the new acylhydrazone ligand.The complex shows rapid and visible solventchromic luminescence triggered by methanol(MeOH)solvent,whereas no response is observed when it is exposed to other volatile organic compounds(VOCs).In comparison with many known vapochromic systems,this complex shows high selectivity for MeOH and ultra-stability for the solvent-driven luminescence.Herein,a simple and low-cost VOCs test papers for monitoring MeOH solvent was developed,as a convenient auxiliary to the complicated VOC sensing systems.