Exploiting Photofunctional Transition Metal Complexes

Youngmin You

Division of Chemical Engineering and Materials Science, Ewha Womans University

odds2@ewha.ac.kr 

An excited state refers to the transient state that conveys energies greater than that of a state in equilibrium with surrounding media. Among various forms of excited states, electronically excited states are of significant importance because they elicit diverse functions. A promising, yet underdeveloped, approach to access excited states is to employ molecules. This approach benefits from the accumulated knowledge of the design and preparation of molecules. The versatility in molecular structures provides tremendous opportunities to create and improve function. 

My group initiated research to explore excited-state molecules. Prime interest is to control and utilize processes involving spin flip during electronic transition (e.g., phosphorescence) or in the excited state (e.g., intersystem crossing). We employ chemistries to approach the challenges. Specifically, we have developed novel classes of molecular emitters, triplet sensitizers, photoredox catalysts, and bioprobes, with combined use of quantum chemistry, organic/organometallic/polymer synthesis techniques, and photophysical and electrochemical methods. Such integrated research has been fruitful. A novel molecular mechanism was devised, which enabled very high quantum yields for photoelectrochemical functionalization of drugs through cycling of both photon and electron. As another example, we established n-p* fluorophore molecules that are capable of harnessing triplet exciton into singlet manifolds for high efficiency fluorescence emission. We also investigated molecular origin for short operation time of blue-phosphorescent organic light-emitting devices. Our mechanistic study revealed that reactive radical ion species could be generated even under balanced carrier injection, and that exciton-mediated intermolecular electron transfer between a host and a dopant was responsible for the generation of such species. Finally, we continue to extend our understanding to application into biological systems. Probes for use in metalloneurochemistry have been developed. In addition, biological utility of photosensitizers that generate singlet oxygen (¹O₂) has been successfully demonstrated.