Multi-Excited-State Phosphorescent Molecules With Photoinduced Structural Changes

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In this project funded by the Chemical Structure, Dynamic & Mechanism B Program of the Chemistry Division, Professor Biwu Ma of the Department of Chemical and Biomedical Engineering at Florida A&M University - Florida State University College of Engineering is developing and studying a new class of phosphorescent metal complexes with interesting photophysical properties. The goal of this research is to gain fundamental understanding of the excited state dynamics and kinetics of these molecules with controlled potential energy surfaces (PES) and photoinduced structural changes (PSC), which have potential applications in various areas, ranging from molecular electronics, solar energy conversion devices, to light emitting diodes. The research contains multidisciplinary elements of molecular design, synthesis, structural characterization, spectroscopy, computation, and device, which is well suited for an integrated education of new generation scientists. The research group has a rich history of training scientists at all levels, including undergraduates and those from underrepresented groups. Outreach activities involving K-12 students are also a part of this project. Photoinduced structural changes (PSC) can lead to the formation of multiple excited states. However, precise control of PSC to create multiple excited states in equilibrium is challenging. The group developed a class of pyrazolate bridged platinum binuclear complexes that possesses multiple excited states in equilibrium as a result of PSC. To further the study of this class of interesting molecules, ultrafast time-resolved emission spectroscopy and transient absorption spectroscopy are utilized to gain fundamental understanding of the optical transactions and structural change processes, and the effects of molecular shape and electronic structure on the excited state dynamics and kinetics of these molecules. In addition, new multi-excited-state photoactive molecules with tunable PES and PSC are synthesized, with which a new type of molecular photosensing devices can be developed, considering their unique capability of converting photonic energy to potential energy to trigger structural rearrangements with distinct optical and electronic properties.