Synthesis And Photophysical Properties Of Pyridazole-based Aggregation-induced Emission Iridium(?)Complexes

Recently,organic luminescent materials are widely used in a variety of applications,such as in flat panel displays,date storage,solar cells,organic light emitting devices(OLEDs)and biological probes owing to their good chemical stability and structural tailorability.The emission properties of solid-state luminescent materials heavily depends on their molecular packing mode.Generally,traditional organic luminescent materials,especially those aromatic molecules,experience intense intermolecular ?-? stacking interactions,which lead to weak emission in the solid state.This phenomenon is termed as “aggregation-caused quenching(ACQ)” effect,which significantly hampers the practical applications of organic luminogens.Various strategies including elaborate physical and chemical approaches have been utilized to prevent or alleviate the ACQ issue,but these attempts are not satisfactory due to the complicated procedures.Fortunately,the discovery of aggregation-induced emission(AIE)by Tang et al.in 2001 has offered a new solution to overcome this drawback and drawn great research attentions.Instead of emission quenching,AIE luminogens are weakly emissive in the dissolved state but a striking enhancement of emission intense is observed in the aggregated or solid state,which paves a new platform for construction of highly efficient solid-state luminogens.On the other hand,for some organic luminogens,with the name of mechanochromic luminescent(MCL)materials,their molecular packing pattern can be altered in response to external stimuli(e.g.pressure,grinding and rubbing),accompanying with the change in the emission color.MCL materials provide a fundamental basis for pressure sensors,memory chips,optical devices,security papers and other functional materials.Phosphorescent Ir(?)complexes are receiving considerable attention due to their high quantum efficiency,long emission lifetimes,large Stokes shifts,good photo-and thermal stabilities as well as tunable luminescent colors.However,Ir(?)complexes also suffer from the notorious effect of aggregation-caused quenching in solid states,which ultimately limits the development of them.Up to now,the development of the AIE luminophores are mainly concentrated on the organic fluorescence molecular,phosphorescent AIE materials are less investigated because of the lack of clear molecular design principles.Thus,it is of great significance to design and synthesis of AIE-active Ir(?)complexes and study their photophysics performances.In this paper,we designed and synthesized a series of new AIE-active pyridazole-based Ir(?)complexes,and their photophyical properties have been investigated in detail.All the relative studies are outline as follows:1.A new design strategy to tune emission colors of AIE-active Ir(?)complexes,by simply adjusting the strength of donor/acceptor on ancillary ligands,is reported.The experimental and theoretical results clearly reveal enhancing the ability of donor/acceptor leads to red-shifted emission and vice versa.2.A series of 2-(1H-tetrazol-5-yl)-based AIE-active Ir(?)complexes are designed and synthesized.The experimental and theoretical results clearly reveal that the frontier molecular orbitals distribution for our designed AIE-active Ir(?)complexes are distinctly difference with reported ones and modifying with cyclometalated ligands brings about a distinct change on LUMO levels which adjusting the HOMO-LUMO energy gaps leads to different emission colors of Ir(?)complexes.In addition,a more blue emitting compound is designed by employing the strategies in our previous and this work.3.A simple and feasible strategy to easily control the mechanochromism of AIE-active Ir(?)phosphors is reported.Changing the dipole moment of the Ir(?)complexes by simply modifying the donors on ancillary ligands can effectively adjust their MCL behaviors.The experimental results reveal that the larger the dipole moments,the more efficient is the mechanochromism for such a studied system.Furthermore,benefiting from the prominent and reversible mechanochromism as well as intense emission in the aggregation state,an efficient data encryption device and a sensitive explosive probe towards 2,4,6-trinitrophenol(TNP)are achieved.4.A new class of Ir(?)complexes is designed and synthesized,which simultaneously exhibits AIE behaviors and MCL properties.They show rich photophysical,AIE and MCL properties,which are well characterized by spectroscopic techniques.The PXRD analysis suggests that the present mechanochromism of Ir(?)complexes is attributed to the transformation from a crystalline to an amorphous phase upon mechanical grinding.