1. Platinium(II) emitters and metal-TADF emitters for OLED applications
Phosphorescent metal complexes have found profound applications in Material Science and that OLED materials for display and lighting are among their most prominent real-world applications because they enjoy a privileged electric-to-light conversion efficiency of up to unity over conventional fluorescent dyes. Our group has a long tradition and research excellence in design and development of original and proprietary phosphorescent platinum(II) complexes for OLED applications of practical interests and has established an array of robust and highly luminescent tridentate and tetradentate platinum(II) systems that emanate visible-light emissions from blue to green and red colors essential for full-color display as well as white and near infrared light emissions. A large majority of our platinum material patents have been licensed to the leading players in the industry, including Samsung and Merck. The next generation of OLED emitters necessitates a full utilization of electrogenerated excitons with short radiative lifetimes to achieve both high light emission efficiency and operational stability, which are currently deficient especially for blue OLEDs. We envisage that metal emitters capable of harvesting singlet emission via thermally activated delay fluorescence (TADF) mechanism is a promising option. Our group in recent years has been in active exploration of novel and efficient metal-TADF emitters and has developed several unprecedented classes of strongly luminescent gold-, which has a much higher abundance than iridium and other noble metals, as well as earth-abundent tungsten-TADF emitters showing radiative lifetimes as short as sub-microsecond and PLQY >80%. The device efficiencies and stability of our gold(III)-TADF emitters are highly competitive with respect to the current best Ir(III) and Pt(II) emitters. |
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2. Photoredox catalysis with transition metal complexes
Photoredox catalysis has emerged as an efficient strategy for achieving solar-to-chemical energy conversion and selective functionalization of organic compounds with complexity under mild reaction conditions. In this regard, we have been developing various types of phosphorescent transition metal complexes including those of Pt(II), Au(III) and Pd(II) with long-lived excited states for catalyzing light-induced organic transformations such as oxidative C–H functionalization and reductive dehalogenation reactions. One of our directions is to employ coordinative-unsaturated metal complexes that activate C–X bonds (X = hydrogen, halogen) upon photo-excitation via an inner-sphere atom abstraction mechanism without the need for sacrificial electron donors/acceptors. Examples of these include binuclear Pt(II) diphosphite complexes (also known as “platinum pop”) and binuclear Au(I) diphosphine complexes. Another direction is to develop photocatalysts based on earth-abundant metals such as copper, tungsten and iron. We reported the use of zwitterionic Cu(I) complexes for light-induced cross-dehydrogenative coupling reactions affording aza-Henry- and Mannich-type products. Air-stable luminescent W(VI) dioxo complexes supported by Schiff base or 8-hydroxyquinolinate ligands also demonstrated photocatalytic activity in oxidative cyanation of tertiary amines and hydroxylation of aryl boronic acids. Very recently, we reported iron porphyrin catalyzed light-driven C–H bond amination and alkene aziridination with organic azides. |
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