Thermodynamic vs. kinetic control of excited-state proton transfer reactions |
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Institution: | 1. Department of Chemistry and Center of Excellence for Innovation in Chemistry (PERCH-CIC), Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand;2. Department of Chemistry, Faculty of Science, King Mongkut''s Institute of Technology Ladkrabang, Bangkok 10520, Thailand;3. Center of Excellence in Materials Science and Technology, Chiang Mai University, Chiang Mai 50200, Thailand |
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Abstract: | The “Excited-State Intramolecular Proton Transfer” (ESIPT) reactions in a number of organic fluorophores are among the fastest basic chemical reactions known so far and their rates can be observed even on femtosecond time scale. Accordingly, the reactant concentration, as monitored by its emission, should be negligibly small. In sharp contrast to this conventional wisdom, however, the coexistence of the reactant and the product of this reaction is so frequently observed in condensed media. We then discuss two possible origins of these effects: when the ESIPT reaction is perturbed and hence is slow on the time scale of emission (kinetic control) or when the reverse reaction repopulating the reactant state is fast and leads to the excited-state equilibrium (thermodynamic control). Upon reviewing a great number of ESIPT prototypical systems, we summarize and discuss different criteria for distinguishing these cases based on the steady-state and time-resolved spectroscopic studies and derive correlations between reversibility of these reactions and the solvent-dependent effects observed in fluorescence spectra. |
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Keywords: | Excited-State Intramolecular Proton Transfer Excited-State Intramolecular Charge Transfer Excited-state reaction Reversibility 3-Hydroxychromones |
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