| Transition metal complexes have been widely employed in optoelectronic fields,such as display devices,information storage,logic gates,and sensors,due to their easily modified chemical structures,good stability,and excellent optical and electronic properties.Among them,phosphorescent iridium(Ⅲ)complexes are considered to be one of the best luminescent materials for organic light-emitting diodes(OLEDs)because of their high luminescent efficiency,tunable emission wavelengths,and relatively short excited-state lifetimes.Especially,red emission is an indispensable chromaticity component of warm white organic light-emitting diodes,which has important application values in the fields of solid-state lighting and information display.In addition,owing to their sensitivity of optoelectronic properties to electrical stimulus,rich charge-transfer excited states and adjustable electrochemical properties,transition metal complexes are also very suitable for the fabrication of resistive memory devices.However,the device performance of such resistive memories needs to be further improved,especially in terms of low power consumption.To solve the above problems,in this thesis,a series of iridium(Ⅲ)complexes,ruthenium(Ⅲ)complexes and porous bimetallic coordination polymers were designed and synthesized by utilizing the easily modified chemical structures.Based on their excellent optoelectronic properties of transition metal complexes,red organic light-emitting diodes and low-power resistive memories were successfully fabricated by optimizing the device structure.The major contents of this thesis include the following four parts:1.In order to achieve red emission,we proposed a molecular design and excited-state tuning strategy for red iridium(Ⅲ)complexes based on the positional isomerization of sulfur atoms in thiophene heterocycles.Thus,a series of efficient neutral red iridium(Ⅲ)complexes Ir1-Ir4 were designed and synthesized by applying thienylquinoline as the cyclometalated ligands,andβ-diketone or 2-picolinic acid as the auxiliary ligands,respectively.Ir1-Ir4 exhibit significantly tunable emission wavelengths from 595 to 670 nm and high solution photoluminescence quantum efficiencies of 0.36～0.82.Taking advantage of the longer emission wavelengths and higher photoluminescence quantum efficiencies of Ir1 and Ir3,two red electroluminescent devices D1 and D2 with excellent performance were prepared,respectively.Devices D1 and D2 exhibit current efficiency,power efficiency and maximum external quantum efficiency of 19.96 cd/A and 25.10 cd/A,20.08 lm/W and 23.63 lm/W,23.85%and 22.12%,respectively,which are better than the previously reported optimal values of red OLEDs based on iridium(Ⅲ)complexes.They have great potential applications in the fields of solid-state lighting and information display in the future.2.Based on the responsiveness of optoelectronic properties to electrical stimulus,rich charge-transfer excited states and adjustable electrochemical properties of iridium(Ⅲ)complexes,two neutral iridium(Ⅲ)complexes Ir5 and Ir6 with 4-methyl-2-(thiophen-2-yl)quinoline as the cyclometalated ligand,and 3-(trifluoromethyl)-5-(2-pyridyl)-1,2,4-triazole or picolinic acid as the auxiliary ligands,respectively,were designed and synthesized for organic resistive memories.The farbricated Al/Ir5/ITO and Al/Ir6/ITO devices exhibit typical non-volatile Flash memory characteristics with ON/OFF current ratios of 10~2～10~3,which is attributed to the intramolecular charge transfer.This work demonstrates the great potential application of iridium(Ⅲ)complexes in future small-molecule nonvolatile memories.3.A novel ruthenium(Ⅱ)complex with donor-acceptor-donor(D-A-D)ligand was designed and synthesized to prepare the organic memory devices.The fabricated ruthenium(Ⅱ)complex-based devices exhibited obvious bipolar resistance switching behavior with low switching voltage(～1.13V)and large ON/OFF ratio(10~5).The switching mechanism can be explained by the distinct charge-transfer states endowed by the interaction between metals and ligands,which is verified by density functional theory calculations.Excitingly,the device displayed a much lower switching voltage than most of the previously reported metal complex-based memory devices due to the intense intramolecular charge transfer induced by the strong built-in electric field in D-A systems.This work provides a new inspiration to manipulate switching voltage at molecular level.4.In order to prepare the solid film suitable for memory devices,we successfully prepared the porous bimetallic coordination polymer(NiCoBDC)nanosheet by using metal-hydroxide nanostructures as the precursors to control the growth of coordination polymer.Owing to the good dispersibility of NiCoBDC nanosheets in ethanol,the Al/NiCoBDC/ITO sandwiched resistive memory device was prepared via a simple solution-processable method.The device exhibits obvious bipolar resistance switching behavior with low switching voltage(-0.5 V),large ON/OFF ratio(>10~2),high stability and good reliability.This study provides a simple method to prepare porous bimetallic coordination polymer nanofilms suitable for device application,and proves the application potential of NiCoBDC nanofilms in electrical memory devices. |
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