期刊
JOURNAL OF PHYSICAL CHEMISTRY B
卷 123, 期 22, 页码 4745-4756出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpcb.9b01475
关键词
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资金
- Royal Society through a Royal Society University Research Fellowship [UF1402310]
- Research Fellows Enhancement Award [RGF\EA\180076]
- EPSRC [EP/P010253/1]
- EPSRC through the Bristol Centre for Functional Nanomaterials [EP/G036780/1]
- EPSRC [1971468, EP/P010253/1] Funding Source: UKRI
The ultrafast dynamics of a bimolecular excited-state proton transfer (ESPT) reaction between the photoacid 7-hydroxy-4-(trifluoromethyl)-1-coumarin (CouOH) and 1-methylimidazole (MI) base in aprotic chloroform-d(1) solution were investigated using ultrafast transient infrared (TRIR) and transient absorption (TA) spectroscopies. The excited-state lifetime of the photoacid in solution is relatively short (52 ps), which at the millimolar photoacid and base concentrations used in our study precludes any diffusion-controlled bimolecular ESPT reactions. This allows the prompt ESPT reaction between hydrogen-bonded CouOH and MI molecules to be studied in isolation and the contact ESPT dynamics to be unambiguously determined. Our time-resolved studies reveal that ultrafast ESPT from the CouOH moiety to hydrogen-bonded MI molecules occurs within similar to 1 ps, tracked by unequivocal spectroscopic signatures of CouO(-)* photoproducts that are formed in tandem with HMI+. Some of the ESPT photoproducts subsequently pi-stack to form exciplexes on a similar to 35 ps time scale, minimizing the attractive Coulombic forces between the oppositely charged aromatic molecules. For the concentrations of CouOH and MI used in our study (up to 8 mM), we saw no evidence for excited-state tautomerization of coumarin anions.
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