Molecular photophysics and laser control: Small molecules to fluorescent proteins

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The research is focused on the development and utilization of theoretical and computational methods for understanding and predicting the structure and properties of molecules underlying biological imaging and new materials as well as for controlling molecular quantum dynamics. Experimental measurements require complementary theoretical and computational study to interpret, and, more importantly, to generalize the observed behaviour to other systems. While the emphasis is on a detailed understanding of excited electronic states, corresponding spectroscopic properties (1-photon absorption, two-photon absorption, fluorescence, phosphorescence,…), and underlying dynamics, the problems to be studied are diverse: (1) Fluorescent proteins are useful probes of biological mechanisms, functions, and structures in molecular and cell biology. There has been great interest in designing FPs with excellent two-photon absorption. We will screen computationally FPs based on non-canonical amino acids (ncAAs) for their two-photon absorption properties. Since the incorporation of ncAAs into proteins is a challenging task experimentally, computational guidance on promising systems is critically important. (2) We will explore recently synthesized fluorescent nucleobase analogs (the natural nucleobases are non-fluorescent) to rationalize the connections between structure and photophysical properties. To assess their use in biological imaging, we will study their binding to natural nucleobases and subsequent effects on absorption/fluorescence properties. (3) Computational tools will be developed for simulating resonance Raman spectra. (4) The BODIPY family of molecules is used widely due to their excellent photophysical properties, i.e., tunable absorption wavelengths, large extinction coefficients, and high quantum yields. Substituted-BODIPY and BODIPY dimers will be examined for a variety of uses, e.g., imaging, molecular photonics… (5) We will compute the photophysical properties of new phosphorescent materials based on bismuth-containing compounds; the rational design of new materials with improved spectral characteristics can save countless experiments. (6) Using tailored laser fields to control quantum dynamics is well-established theoretically and experimentally. The on-going development of shaped laser sources from the mid-infrared to the ultraviolet has lead to the control of a diversity of photophysical and photochemical phenomena, e.g., rovibrational and/or electronic state population transfer, photoisomerization. An important complement to these many experiments is a detailed understanding of the mechanism(s) leading to control. The proposed research will further develop and apply methods for examining laser control in polyatomic molecules. Applications will include photoisomerization and, in particular, photoswitchable proteins.