The Synthesis And Luminescence Behavior Modulation Of Iridium(?)and Platinum(?)Complexes Containing Imidazole Unit Ligands

The luminescent Ir(?)and Pt(?)complexes have attracted considerable attention due to their potential applications in chemosensors,phosphorescent emitters in organic light-emitting diodes(OLEDs),cellular imaging,information storage and security protection,etc.In order to regulate the luminescence behaviors of Ir(?)and Pt(?)complexes,two main methods are commonly used,including introducing different organic groups to in their molecular structures,and using external stimuli(e.g.,light,grinding,anion exchanging,heating or pH,etc.)to modify the structures of these complexes.Based on the two methods,we designed and synthesized some Ir(?)and Pt(?)complexes containing bisthienylethene ligands,or quinoline-benzimidazole-based N^N ancillary ligands,and studied the structures and luminescence behavior of these complexes.The related study works mainly include the following three parts.1.Complexes LIr(dfppy)2(BrL)]·3CH3OH(1)and[Pt(dfppy)(BrL)]-CH3OH(2)have been prepared based on dfppyH and bisthienylethene BrLH.The CH2Cl2 solution of 2 reveals photochromism,changing its color from nearly colorless to light green upon irradiation with 380 nm light.This photochromism can result in the decrease in phosphorescence emission intensity of 2.In contrast,compound 1 has not shown photochromic behavior,which could be mainly due to the energy transfer of the UV excitation energy to the {Ir(dfppy)2}+ unit,and/or assigned to insufficient space to allow photocyclization of the BrL-ligand to take place.At room temperature,both 1 and 2 are luminescent in CH2Cl2 solution,showing strong phosphorescence emissions at 495 and 513 nm with predominant 3MLCT character for the former,while relatively weak phosphorescence emission at 508 nm with predominant 3LC character for the latter.In addition,compound 1 is luminescent in solid state with an emission at 524 nm.On the contrary,compound 2 is almost non-luminescent in solid state,due to the molecule-aggregation-induced luminescence quenching.Clearly,1 and 2 are significantly different in crystal structures,photochromism,and luminescence behaviors.This indicates that the variation of metal center is one of effective approaches to modify the photochromism and/or luminescence of metal bisthienylethene complexes.2.We prepared bisthienylethenes tBuLH and tBuLMeH containing the substituent groups-C(CH3)3 and/or-CH3,and their complexes[Ir(dfppy)2(tBuL)]·2CH3OH(3)and Ir(dfppy)2(tBuLMe)](4).Both tBuLH and tBuLMeH reveal photochromic behaviors in CH2Cl2,with a color change from colorless to yellowish-brown upon UV irradiation with 326/321 nm light.The absence of photochromism in both 3 and 4 indicates that the coordination of tBuL-/tBuLMe-ligand to {Ir(dfppy)2}+ unit could suppress its photochromic behavior,mainly due to the energy transfer of the UV excitation energy to the {Ir-(dfppy)2}+ unit,and/or because of insufficient space to allow photocyclization of the tBuL-/tBuLMe-ligand to take place.The phosphorescence emissions of 3(514 nm)and 4(507 nm)have mixed 3MLCT and 3LC character.The luminescence spectra indicated that the emissions of 3 and 4 have relatively less 3MLCT character compared to the reported[Ir(dfppy)2(L1)]·2CH3OH.Our experimental results demonstrate that the substituent groups-C(CH3)3 and/or-CH3 in 3 and 4 could significantly modify the structures,photochromism and luminescence of the complexes.3.Four new cyclometalated Ir(?)complexes[Ir(dfppy)2(qbiH)](PF6)(5),[Ir(dfppy)2(qbim)](PF6)·H2O(6),[Ir(dfppy)2(qbio)](PF6)(7)and[Ir(dfppy)2(qbi)](8)have been obtained based on dfppyH and quinoline-benzimidazole-based N^N ligands qbiH,qbim and qbio.In the crystal structures of 5-7,each {Ir(dfppy)2}+ unit is coordinated by a neutral qbiH/qbim/qbio ligand,forming cationic Ir(?)complex.In contrast,an {Ir(dfppy)2}+ unit in 8 is coordinated by a qbi-anion,obtaining a neutral Ir(?)complex.In CH2Cl2,compound 5 shows the phosphorescence emissions at 558 and 585 nm,and compounds 6 and 7 reveal the similar emissions at 572/573 nm and 600 nm.This indicates that the introduction of electron-donating CH3/n-C8H17 group in 6 and 7 can lead to their red-shifted emissions(?? around 15 nm)compared to the emissions of 5.In addition,the similar emissions for 6 and 7 indicate that the carbon-atom number of CH3/n-C8H17 group almost has no influence on their emission wavelengths.Compared to 5,compound 8 shows a relatively weak emission at 546 nm.Interestingly,both 5 and 8 can switch their luminescence between strong luminescence state with emission at 558 nm and weak luminescence state with emission at 546 nm upon addition of NEt3/TFA,which is assigned to their structural interconversion.Our experimental results demonstrate that the structures and luminescence of 5-8 can be modulated by varying substituent group or protonation/deprotonation state of their imidazole units.