What is it about?
The ESPT reaction of pyrene-urea compounds in DMSO and in DMF was compared. Unlike in DMSO, the addition of cyclodextrin in DMF greatly reduced tautomer fluorescence (T*). This confirms the existence of a specific hydrogen bond between DMSO and the urea compound.
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Why is it important?
The fluorescence intensity of T* relative to normal form (N*) was maximal in DMSO, and the ESPT reaction rate constant was also maximal in DMSO based on fluorescence lifetime measurements. On the other hand, the inverse ESPT reaction rate constant would be expected to be slowest when T* takes the most stable conformation in DMSO. However, the fact that it was largest in DMSO could not be explained by simply considering the energy level alone.
Perspectives
Unlike in DMSO, the reverse ESPT reaction was not observed in DMF because it is very slow. This may be due to the specific hydrogen bonding interaction of DMF on T*. Thus, hydrogen bonding with the solvent has a significant effect on the ESPT reaction. It is very important to investigate the cause of this phenomenon in order to clarify the ESPT reaction mechanism of aromatic urea compounds.
Professor Yoshinobu Nishimura
nishimura@chem.tsukuba.ac.jp
Read the Original
This page is a summary of: The effect of DMSO on the intermolecular proton transfer reaction of urea–β-CD, Journal of Molecular Liquids, March 2024, Elsevier,
DOI: 10.1016/j.molliq.2024.124268.
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