Design, Synthesis, Photophysical Properties And The Application Of Phosphorescent Iridium (â…¢) Complexs With Triarylboron Moieties

Phosphorescent Ir（III） complexes have attracted much research interests in recent year due to their excellent photophysical properties, such as high luminescence efficiencies and significant Stokes shifts. However, the most outstanding characteristic of Ir（III） complexes might be the variability of the electro-optical properties. Their metal–ligand-based luminescence provides the opportunity to tune the emission color over the whole visible （even near-infrared） range by changing the chemical structures of ligands. All these merits make iridium（III） complexes highly appealing as phosphors in multicolor organic light emitting diodes （OLEDs）, light-emitting electrochemical cells （LECs）, sensing, biolabeling, etc. As we know, triarylborane derivatives have received wide interests in the past decades, since they are highly attractive as anion sensors, ion/electron-conduction, light-emitting, optoelectronic, and nonlinear optical materials. As a new trend of research along the line mentioned above, several groups have recently demonstrated that transition-metal complexes with arylborane ligands show spectroscopic and photophysical properties different from those without arylborane ligands. This suggests that such transition-metal complexes could be possible candidates for new ion sensors and light-emitting materials. In this thesis, we designed and synthesized an excellent class of cationic Ir（III） complexes with triarylboron moieties, and realized their application in phosphorescent anion sensors and LECs.1. Synthesis and photophysical properties of a iridium（III） complex containing triarylboron moieties with conjugated D-A structure and its application in F- sensingA novel cationic Ir（III） complex [Ir（Bpq）₂（CzbpyCz）]PF₆ （Ir1） containing containing triarylboron moieties with conjugated D-A structure has been designed and synthesized. The excited-state properties of Ir1 were investigated through UV-vis absorption spectrum, photoluminescence spectrum and molecular orbital calculations. This complex displayed highly efficient orange-red phosphorescent emission with emission wavelength of 583 nm and quantum efficiency of 0.75 at room temperature. The binding of F- to Ir1 can quench the phosphorescent emission from Ir（Ш） complex and enhance the fluorescent emission from N^N ligand, corresponding to a visual change in the emission color from orange-red to blue and realizing colorimetric as well as ratiometric ?uoride sensing. Interestingly, an unusual intense absorption band in the visible region was observed. And the detection of F- can also be carried out with visible light as excitation wavelength.2. Synthesis and photophysical properties of a iridium（III） complex containing triarylboron moieties with unconjugated D-A structure and its application in F- sensingA cationic iridium（III） complex [Ir（Bpq）₂（pbi）（CzFCz）]PF₆ （pbi = 2-（pyridin-2-yl）-1H-benzo[d]imidazole） （Ir2） containing triarylboron moieties with unconjugated D-A structure based on carbazole-fluorene-carbazole （CzFCz） as fluorescent donor and cationic Ir（III） complex unit containing dimesitylboryl （BMes2） groups as phosphorescent acceptor has been designed and synthesized. Several reference compounds, such as [Ir（pq）₂（pbi）（CzFCz）]PF₆ （pq = 2-phenylquinoline pbi = 2-（pyridin-2-yl）-1H-benzo[d]imidazole） （Ir3） similar to complex Ir2 but without BMes2 groups, fluorescent donor CzFCz, and phosphorescent acceptor [Ir（Bpq）₂（pbi）]PF₆ （A2） and [Ir（pq）₂（pbi）]PF₆ （A3）, were also synthesized in order to better understand the influence of BMes2 groups on the excited state properties and fluorescence resonance energy transfer （FRET） in this system. The introduction of BMes2 groups on the ligands of Ir（III） complex unit can lead to the red-shifted and more intense absorption, facilitating efficient FRET from fluorescent donor to phosphorescent acceptor. Ir2 displayed highly efficient orange-red phosphorescent emission with emission peak of 584 nm in CH2Cl2 solution at room temperature. The emission wavelength of complex Ir2 in film is red-shifted to 600 nm with a shoulder at 650 nm, and its quantum efficiency in film was measured to be 0.15 under excitation at 450 nm. Utilizing the specific Lewis acid-base interactions between boron atom and F-, the binding of F- to complex Ir2 can change its excited state and suppress FRET, quenching the phosphorescent emission from Ir（III） complex and enhancing the fluorescent emission from CzFCz. Thus, a visual change in the emission color from orange-red to blue was observed. Optical responses of complex Ir2 to F- revealed that it can be used as a highly selective, colorimetric and ratiometric optical probe for F- utilizing the switchable phosphorescence and fluorescence.3. Synthesis and photophysical properties of a dinulear iridium（III） complex containing both triarylboron moieties and its application in F- sensingWe designed and synthesized a conjugated oligomer （dL） with two N^N coordination sites, and a dinuclear cationtic Ir（III） complex （dIr） with BMes2 moieties. The photophysical properties of dIr and dL were investigated through UV-vis absorption spectrum, photoluminescence spectrum and molecular orbital calculations. In CH2Cl2 solution, dL displayed strong blue emission at 457 nm, and the quantum efficiency is 0.76. And the complex dIr displayed highly efficiency orange-red phosphorescent emission with emission wavelength of 590 nm and quantum efficiency of 0.27 at room temperature. The binding of ?uoride （F-） to dIr can quench the phosphorescent emission from Ir（Ш） complex and realizing―ON-OFF‖F- sensing.4. Near-infrared phosphorescent probe for F- based on a iridium（III） complex with triarylboron moietiesWe designed and synthesized a near-infrared （NIR） phosphorescent probe for fluoride based on a cationic Ir（III） complex [Ir（Bpq）₂（quqo）]PF₆ （Ir4） with dimesitylboryl （BMes2） groups on the cyclometalated C^N ligands （Bpq） and 2-（quinolin-2-yl）quinoxaline （quqo） as N^N ligand. The excited state properties of Ir4 were investigated through UV-vis absorption spectrum, photoluminescence spectrum and molecular orbital calculations. Upon excitation, complex Ir4 shows NIR phosphorescent emission around 680 nm. Interestingly, the complex can be excited with long wavelength around 610 nm. Such long-wavelength excitation can reduce the background emission interference and improve the signal-to-noise ratio. Furthermore, the selective binding between boron atom and fluoride can give rise to the quenching of emission and realize the near-infrared phosphorescent sensing for fluoride.5. Two-photon properties of a dinulear iridium（III） complex containing triarylboron moieties and its application in two-photon fluoride sensingWe investigated two-photon-induced photophysical properties of dinulear cationic iridium（III） complex （dIr）, Ir0 and the free N^N ligand dL. When excited at 800 nm, dL displayed strong blue emission around 465 nm. Ir0 and dIr displayed orange-red emission around 600 and 606 nm, respectively. The complex dIr and the free ligand dL exhibited strong two-photon-induced emission and the maximum two-photon absorption cross-sections of them were measured to be 481 and 195 GM, respectively. Because of the interaction of triarylborane with fluoride anions, the binding of ?uoride to dIr can quench the two-photon-induced phosphorescent emission from Ir（Ш） complex and realized two-photon-induced―ON-OFF‖phosphorescent sensors for fluride. An ionic transition-metal complex for improved charge transporting properties was designed, containing both n-type dimesitylboryl （BMes2） and p-type carbazole groups. The complex, [Ir（Bpq）₂（CzbpyCz）]PF₆（Ir1） （Bpq = 2-[4-（dimesitylboryl）phenyl] quinoline, CzbpyCz = 5,5’-bis（9-hexyl-9H-carbazol-3-yl）-2,2’-bipyridine） and its equivalent in which the BMes2 groups were substituted with carbazole moieties were evaluated on the photoluminescence and excited state properties in detail. According to the photophysical and electrochemical properties, we concluded that the BMes2 groups can increase the conjugation length of the cyclometalated C^N ligands more effectively by enhanced pÏ€-Ï€* conjugation than carbazole groups, leading to the red shift of both absorption and emission spectra. In addition, the bulky BMes2 groups are effective in preventing the molecular aggregation in film. Both complexes were used to prepare single component LECs. The electroluminescent devices show the typical behavior of LECs. The LEC based on the complex containing both electron- and hole-transporting groups shows the best performance. This work demonstrated that the design and synthesis of p-n metallophosphor will be beneficial for the improvement of device performances.