Synthesis And Properties Of Carborane-based Phosphorescent Iridium(â…¢) Complexes

Phosphorescent Iridium complexes have been widely used in the field of organic electroluminescence, chemical sensing and bio-imaging due to the excellent photophysical properties. However, with the recent ten years of rapid development, the research space of such phosphorescent iridium complexes have become saturated from their structur’e, emitting mechanism and applications. Therefore, the development of phosphorescent iridium complexes with new structures and excellent performance is a huge challenge. To tune or improve the properties of the material, icosahedral carboranes have been recently introduced into various optical functional molecular material by the form of a skeleton or a functional group due to their stable three-dimensional structure and special electronic properties. Nevertheless, the adjustment of carboranes on photophysical properties of optical functional moleculars has not been studied thoroughly, and many unique photophysical properties are difficult to explain.The involvement of carborane functional groups in the field of optoelectronic materials has just begun, and is almost a blank in the field of optical functional metal complexes. Therefore, to develop new and multifunctional phosphorescent iridium complex materials and study the roles of carborane functional groups on photophysical properties of complex, this paper aims to introduce carborane functional group into various classic phosphorescent iridium complexes. The specific contents unfold in following three parts:1. Study on photophysical properties of carborane-functionalized neutral and cationic iridium complexesThis chapter firstly introduce o-, m-or p-carborane isomers into classic phosphorescent neutral iridium complex Ir(ppy)2acac and cationic iridium complex [Ir(ppy)2phen]PF6with4-position of benzene ring of cyclometalated ligand ppy and investigate the effects of three carboranes isomers on photophysical properties of these complexes. It is showed that o-carborane was observed to quench the phosphorescent emission in neutral complexes, but m-and p-carboranes can strongly enhance emission both in solution and solid state. In the case of cationic complexes the three carborane isomers can both increase quantum yields and significantly adjust emission wavelengths of these complexes. In addition, we explain the above photophysical properties through electrochemical and quantum chemical calculations.2. Study on photophysical properties of carborane-based tris-cyclometalated facial and meridional iridium complexes and application in the cellular bioimagingThis chapter firstly introduce o-, m-or p-carborane isomers into classic tris-cyclometalated facial iridium complex fac-Ir(ppy)3and meridional iridium complex mer-Ir(ppy)3with4-position of benzene ring of cyclometalated ligand ppy and investigate the effects of three carboranes isomers on photophysical properties of these complexes. It is discovered that m-and p-carboranes can improve luminescent efficiency of these complexes. However, the effect of o-carborane in the facial complex shows media-dependence both in solution and solid state that conversely correlates to dielectric constant, thus showing strong emission in small dielectric constant media, whereas quenched emission in large dielectric constant media. Furthermore, the hydrophilic nido-carborane-functionalized iridium(III) complex has been prepared, which has high phosphorescence efficiency and long emission lifetime in aqueous solution, thus has been successfully applied in bioimaging, especially in fluorescence lifetime imaging.3. Study on photophysical properties of carborane-based neutral and cationic Iridium tetrazolate complexes and application in the cellular bioimagingThis chapter firstly introduce o-, m-or p-carborane isomers into neutral iridium tetrazolate complex Ir(ppy)2TZ and cationic iridium tetrazolate complex [Ir(ppy)2TZ]PF6with4-position or5-position of benzene ring of cyclometalated ligand ppy and investigate the effects of three carboranes isomers on photophysical properties of these complexes. The results demonstrate that the emission of carborane-based neutral iridium complexes exhibit a red shift at4-position and a blue shift at5-position, of which, o-carborane derivatives show the maximum change. In the case of cationic complexes, all carborane-based complexes exhibited a blue shift whether4-position or5-position. In addition, the hydrophilic nido-carborane-based iridium(Ⅲ) complex has been prepared, which has a good sense of O2in aqueous solution, thus has been successfully applied in bioimaging and fluorescence lifetime imaging under different oxygen content.