Student Invited Lecture Series: Chong Fang

Structural dynamics of condensed-phase systems such as proteins and sensors govern their functions which broadly impact the chemical, biological, energy and health fields. However, a complete understanding of their working mechanisms is hindered by the lack of suitable tools that can resolve atomic motions on intrinsic molecular timescales. This talk discusses the table-top wavelength-tunable femtosecond stimulated Raman spectroscopy (FSRS), aided by transient absorption spectroscopy and quantum calculations/molecular dynamics simulations, which have captured molecular movies for fluorescence and other nonradiative events like never before. Representative examples include the green and yellow fluorescent protein (GFP/YFP) from jellyfish that can be engineered to emit from blue, green to red and sense calcium (Ca2+) and chloride ions (Cl–) in a ratiometric manner, revealing the ultrafast interplay between excited-state events such as proton transfer, cis-trans isomerization, dark state formation, and conformational trapping (rigidity) or switching (flexibility). Such mechanistic understandings have propelled us to delineate the multidimensional excited-state potential energy surface (such as the Franck-Condon excess energy “kicking” proton transfer) and rationally design and engineer FP-based biosensors and phototransformable FPs as well as other light-driven systems with strategic substitutions and improved or novel functions.