Fluorescence Lifetime Imaging Microscopy (FLIM) as a Tool to Understand Chemical Reactions and Catalysis

Fluorescence lifetime imaging microscopy (FLIM) is an emerging tool to characterize ongoing chemical reactions in synthetic chemistry and catalysis. Initially applied to biological systems, FLIM now reveals spatially resolved chemical reaction species and system-wide physiochemical changes that accompany ongoing reactions. FLIM combines the advantage of environmental sensitivity with high signal sensitivity (as sensitive as single molecules) and has the key ability to operate under synthetic conditions (e.g., high concentrations of reagents, in organic solvents, under ambient temperature and pressure, in opaque mixtures, and in multiphasic systems). Chemical reactions inherently induce changes in the reaction medium, neighboring compounds, surface compositions, and/or bonding structure of the compounds involved, resulting in environmental changes. The FLIM methods recently developed harness and interpret these changes in ways that lead to characterizing compounds and enhancing a mechanistic understanding. Here, current advantages and limitations of FLIM methods are considered, common factors influencing fluorescence lifetime in chemical systems are discussed in a tutorial format, and seven research case studies are strategically analyzed, chosen to highlight how FLIM provided complementary information to understand chemical reaction mechanisms, intermediates, product distributions, partitioning, roles of reagents, and catalyst behaviors. These data and insights obtained from FLIM assist in the rational design and optimization of synthetic and catalytic methods.