Molecular Design, Synthesis and Optoelectronic Properties of light function iridium complexes
|Keywords||iridium(III) complexes phosphorescence PLEDs chemical sensor|
Recently, iridium（Ⅲ） complexes have received considerable attention due to theirhigh emission efficiencies and easy tuning of emission colors by changing chemicalstructures of ligands. In this thesis, seven series of novel iridium（Ⅲ） complexes weresynthesized （Please see the table attached for the molecular structures）. Firstly, theinfluences of chemical structures of ligands on the photophysical and electrochemicalproperties of complexes were investigated in detail. Secondly, efficientelectrophosphorescent polymer-based light-emitting diodes （PLEDs） were fabricatedby doping the iridium（Ⅲ） complexes into the polymer host. Finally, the application ofiridium（Ⅲ） complexes in the field of chemical sensors has been developed.This thesis can be divided into six parts.1. Design, synthesis and optoelectronic properties of a series of iridium（Ⅲ）complexes based on quinoline derivatives and differentβ-diketonate ligands.A series of cyclometalated iridium（Ⅲ） complexes Ir（C^N）2（O^O） based onquinoline derivatives （C^N） and differentβ-diketonate ligands （O^O） weresynthesized, where O^O denotes acetylacetonate （acac） and1-phenyl-2-methyl-4-isobutyryl-5-pyrazolonate （PMIP）. By modifying the chemicalstructures of quinoline derivative ligands, the emissive wavelengths of complexes canbe tuned from 596 to 634 nm. Interestingly, the photoluminescence quantumefficiency can be improved by the replacement of acac with PMIP. Moreover, threeiridium complexes were used as dopants to fabricated electrophosphorescentpolymer-based light-emitting.diodes （PLEDs）. The PLEDs show red emission withhigh external quantum efficiencies, ranging from 7.0 to 9.6%.2. Design, synthesis and aggregation-induced phosphorescent emission （AIPE）of a series of iridium（Ⅲ） complexes containing different ancillary ligands.We have synthesized a series of iridium（Ⅲ） complexes Ir（ppy）2（O^O） containingβ-diketonate ligands （O^O） with different triplet energy levels, where ppy denotes2-phenyl-pyridine. In solution, complexes containingβ-diketonate ligands with hightriplet energy levels exhibit strong phosphorescent emission. When the triplet energylevels ofβ-diketonate ligands were lower than the energy level of 3MLppyCT, noemission was observed for complexes. Interestingly, in solid state moderately strongemission could be observed for those complexes without emission in solution. Weinvestigated the different emission properties of complexes between in solution and in solid state and found that the strongπ-πinteraction between the adjacent pyridyl ringsof ppy ligands is essential in the aggregation-induced phosphorescent emission. Westudied the interesting AIPE by experimental methods and theoretical calculation, andprovided new emission mechanism. We think that the strongπ-πinteraction betweenthe adjacent pyridyl rings of ppy ligands elongates the overallπ-conjugation degreeand reduces the energy levels ofπppy* compared with that in solution. As a result, thetriplet energy level of charge transfer state from iridium to the interacting ppy（donated as 3MLπCT） is reduced and the ppy ligands participate in the excited state insolid state. And emission could be observed.3. Design, synthesis and emission properties of novel cationic iridium（Ⅲ）complexes with different N^N ligands.A series of new cationic iridium（Ⅲ） complexes [Ir（piq）2（N^N）]+PF6- （1-6） （piq=1-phenyl-isoquinoline） containing N^N ligands with different conjugated lengthwere synthesized. UV-vis, photoluminescence, cyclic voltammetry and theoreticalcalculation were employed for studying the photophysical and electrochemicalproperties. And the excited state properties were investigated in detail. The excitedstate of complexes is complicated and contains triplet metal-to-ligand charge transfer（3MLCT）, triplet ligand-to-ligand charge transfer （3LLCT） and ligand centred（cyclometalated） （3LC） transitions simultaneously. In addition, the emissionwavelength can be tuned significantly from 586 to 732 nm by changing theconjugated length of N^N ligands.In addition, we replaced piq with another kind of C^N ligand2,4-difluorophenyl-pyridine （F2ppy） and synthesized a series of new cationiciridium（Ⅲ） complexes [Ir（F2ppy）2（N^N）]+PF6-. By changing the N^N ligands simply,the emission colors of complexes can be tuned from blue （457 nm） to red （590 nm）.4. A highly selective and muitisignaling optical-electrochemical sensor for Hg2+based on phoephorescent iridium（Ⅲ） complex.Because Hg2+ can easily combine with sulfur, a highly selective phosphorescentchemosensor for Hg2+ based on iridium （Ⅲ） complex Ir（btp）2（acac） was realized.Multisignaling changes were observed through UV-vis absorption, phosphorescentemission and electrochemical measurements. Upon addition of Hg2+, the obviousspectral blue-shifts in absorption and phosphorescent emission bands were measuredfor Ir（btp）2（acac）, which could be observed by the naked eyes.5. Design and synthesis of cationic iridium（Ⅲ） complexes based on phenanthroline derivatives and their applications in chemical sensor for anions.A series of new cationic iridium （Ⅲ） complexes containing different phenanthrolinederivatives were synthesized. Their photophysical and electrochemical propertieswere investigated. The influences of anions and proton on the photophysical andelectrochemical properties were also studied in detail. After the addition of CF3COOH,the emission wavelengths were red-shifted evidently and the emission colors werechanged from yellow to deep red. In addition, the addition of F-, CH3COO- can alsocause significant variations of UV-Vis absorption and emission spectra. The solutioncolors of complex 2, 3 and 4 were changed from yellow-green to brown, which can beobserved by the naked eye. The emission of complexes was quenched completely bythe addition of F- and CH3COO-. Especially, complex 2 prefers to bind F- over theother anions, suggesting that complex 2 can be acted as a good phosphorescentchemosensor for F-.6. Highly selective phosphorescent chemosensor for fluoride ions based onnovel iridium（Ⅲ） complexes containing aryiboranes.As the strong Lewis acid, boron atom exhibits the strong affinity toward fluride ionaccording to specific Lewis acid-base interaction. Herein, we synthesized quinolinederivative ligand containing arylboranes and two iridium（Ⅲ） complexes based on thisligand and studied their photophysical and electrochemical properties. In addition, thequinoline derivative ligand and iridium（Ⅲ） complexes can act as the highly selectivechemosensors for F-.