Electrical Stimulus-responsive Phosphorescent Iridium Complexes: Design, Synthesis And Optoelectronic Properties

Electrical field is an important external stimulus since it can be easily combined with the current semiconductor technology. Electrical stimulus-responsive phosphorescent materials have attracted researcher’ attentions due to their potential applications in display devices, sensors, information storage and logic gates. Phosphorescent iridium(III) complexes have been widely applied in organic light emitting diodes, organic electronic memory devices, chemical sensors, bio-imaging and so on, due to their excellent photophysical properties, such as high phosphorescence quantum efficiency, long emission lifetime, easily tunable emission wavelength and rich excited-state properties. The luminescence properties of transition-metal complexes are not only dependent on the metal center and ligand structures, but also very sensitive to the external environment. Currently, most of tuning strategies of photophysical properties for phosphorescent iridium(III) complexes are mainly the synthesis of new ligands or chemical modification of ligand skeleton. However, these strategies generally require complex chemical reactions or harsh reaction conditions. Thus these tuning strategies limit the further development of phosphorescent iridium(III) complexes. Since the photophysical properties of phosphorescent iridium(III) complexes are responsive to external environment, the use of external stimuli to tune their properties is a simple and effective mean. This paper aims to develop stimulus-responsive phosphorescent materials and exploit their applications in optoelectronic devices. This thesis can be divided into four parts.1. Design, tunable photophysical properties and electrochromic phosphorescence of ionic iridium(III) complexes with different counterionsIn our previous work, a series of ionic iridium(III) complexes sharing the same phosphorescent iridium(III) cation with a N-H moiety in the N^N ligand and containing different counterions, have been designed and synthesized. The emission wavelengths of the iridium(III) complexes can be tuned by choosing different counterions, however, the tuning range of emission wavelength(~ 50 nm) between two complexes is limited. In order to achieve a wide range of emission wavelength tuning, a series of ionic iridium(III) complexes with different counterions have been designed and synthesized by selecting a N^N ligand with two hydrogen bond acceptors. The interactions between the complex cation and counterion are not only electrostatic interactions, but also have interesting hydrogen bonding. The photophysical properties of the iridium(III) complexes have been effectively tuned by forming different hydrogen bond strength between the complex cation and counterion. The tuning range of emission wavelength from 493 nm to 591 nm(~ 100 nm) has been achieved. It is worth noting that, an electric field-induced phosphorescence tuning of the complex has been realized by changing hydrogen bond strength under electric field. An information recording and storage device has been constructed via using the electrochoromic phosphorescence.2. Design, synthesis and electrochromic phosphorescence of ionic iridium(III) complex with hydroxyl functional groupIn order to better understand the mechanism of electrochromic phosphorescence, an iridium(III) complex with hydroxyl functional group has been designed and synthesized. The luminescence properties of the iridium(III) complex are not only responsive to concentration and pH value, but also show electrical stimulus-induced phosphorescence change. The change behavior has been explained and demonstrated by using theoretical calculations and NMR analysis. Based on the interesting electrochromic phosphorescence, a quasi-solid information recording and storage device has been constructed. Additionally, the information storage device with security protection has been realized by taking advantage of long phosphorescence lifetime and time-resolved imaging techniques.3. Design, synthesis and additional ion-assisted electrochromic phosphorescence of neutral iridium(III) complexAccording to the difference of chemical structure, the phosphorescent iridium(III) complexes can be divided into ionic and neutral ones. Herein, a series of neutral complexes with hydrogen bond acceptor(-NH) have been synthesized in order to study electrochromic phosphorescence. The phosphorescence properties of the neutral complexes are not dependent on the electric field, but they exhibit electrochromic phosphorescence after adding tetrabutylammonium salt. The research results demonstrate the key role of ion migration for the electrochromic phosphorescence of neutral complexes. The electrochromic phosphorescence can be achieved from ionic complexes to neutral complexes, and the material system based on electrochromic phosphorescence has been further developed. The electrochromic phosphorescence with different emission colors has been realized by modifying ligand structure of the complexes. The research results demonstrate that the neutral complexes with hydrogen bond acceptor can also show electrochromic phosphorescence by adding ionic salts.4. Design, synthesis and molecular switch of the iridium(III) complexes with arylboron functional groupTriarylboron materials have become an important optoelectronic material due to their interesting optical and electrical properties. By taking advantage of the excellent properties of triarylboron materials, two iridium(III) complexes with triarylboron functional group have been designed and synthesized. Their phosphorescence properties are response to fluoride ions due to the Lewis acid-base interaction, resulting in luminescence quenching. Furthermore, the B-F bonding which is sensitive to electric field, can be ruptured under an electric field, restoring the phosphorescence. Based on the phosphorescence change, a phosphorescent molecular switch has been achieved. Thus with F- and an electric field as two inputs, a logic gate has been constructed.