Synthesis Of Novel Fluorinated Cyclometalated Iridium(Ⅲ) Complexes And Study On Their Luminescent Oxygen Sensing

Molecular oxygen plays an important role in life. Thus, the determination of oxygen is important in various fields such as environmental monitoring, clinical analysis, oceanography, and so on. Optical methods with excellent performances have attracted a great deal of interests for the determination of oxygen in the past decades. Cyclometalated iridium(Ⅲ) are very appealing due to both their excited state lifetime on the microsecond time-scale and the triplet character of their emission, high photoluminescence quantum yield, good chemical, photo- and electrochemical stability, and unique capability to have emission tuned over the entire visible spectrum. The potential of Ir(Ⅲ) complexes in optical devices is determined by their molecular structures. Therefore, it is of great importance to investigate the structure-function relationship of the Ir(Ⅲ) complexes in detail and to investigate the possibilities of tuning, for example, by substitution of known compounds for the design of OSPs.Trifluoromethyl (-CF3) group is a strong electron-withdrawing and important substitute in numerous organic electroluminescence materials. It is an important consideration for increasing the quantum yield and photostability of the complexes. To date, all cyclometalated iridium dyes used for oxygen sensing are red or green emitters. However, the ability of these complexes to have emission color tuned over the entire visible spectrum is attractive for developing oxygen sensitive blue dyes. We expect the introduction of a phosphoryl substituent (P=O) to the dfppy could lower the HOMO energy level and tune the emission of iridium complex to the blue region, remaining high quantum efficiencies. To the best of our knowledge, no examples of trifluoromethyl-substituted or phosphoryl-substituted cyclometalated Ir(Ⅲ) complexes for efficient oxygen sensing have yet been reported. Therefore, further investigation is necessary to elucidate the merits of the trifluoromethyl and phosphoryl modified cyclometalated Ir(Ⅲ) complexes for oxygen sensing. The main contents are as follows:1. Trifluoromethyl-substituted cyclometalated Ir(Ⅲ) complexes have been prepared and fully characterized. All complexes exhibit intense phosphorescence emissions at room temperature with λmax in a range of 523-554 nm. Relative to the model complex Ir(ppy)2(acac), these iridium complexes exhibit high maximum quantum yields and good photostability against continuous irradiation. All Ir(Ⅲ) complexes immobilized in ethyl cellulose demonstrated quick responses to various oxygen concentrations and high sensitivity on changes of oxygen partial pressures. The O2 sensitivity (Stern-Volmer quenching constant) of the complexes was quantitatively evaluated in polymer films. The Ksvapp values of OSPs are from 0.00583 Torr-1 to 0.00866 Torr-1, and fast response time and recovery time are found for the sensing films. These cyclometalated Ir(Ⅲ) complexes with high photostability are potential candidates for online continuous monitoring of oxygen concentrations.2. New blue iridium complexes with a phosphoryl substituent have been synthesized and fully characterized. The relationship of structure-photoelectric properties of the blue Ir(Ⅲ) complexes has been investigated. All complexes exhibit intense phosphorescence emissions at room temperature with λmax in a range of 455 - 477 nm. All Ir(Ⅲ) complexes demonstrated quick responses to various oxygen concentrations and high sensitivity on changes of oxygen partial pressures. The O2 sensitivity (Stern-Volmer quenching constant) of the complexes was quantitatively evaluated in polymer films. The KSVapp values of OSPs are from 0.00459 Torr-1 to 0.00793 Torr-1, and fast response time and recovery were found for the sensing films. This study will be helpful for the rational design of new blue transition-metal complexes in luminescent oxygen sensors.