Solvent Effects on Excited State Intramolecular Proton Transfer of One Benzoxazole Derivative
The excited state intramolecular proton transfer(ESIPT)reactions of one benzoxazole derivative,2-{4-[2-(2-methoxy ethoxy)-ethyl]-[(2-methoxy ethoxy)-amino]-phenyl}-5-(5-trifluoromethyl-benzooxazole)-benzofuran-6-ol(MMTB)were studied by density functional theory(DFT)and time-dependent density functional theory(TD-DFT)at the level of PBE0/6-31+G(d,p)in different solvents,such as toluene(PhMe),ethanol(EtOH)and dimethyl sulfoxide(DMSO).The effects of solvent polarity on ESIPT mechanism of MMTB were investigated.It is found that the enol form is stable in the ground states(S0)while two stable configurations(enol and keto forms)are existed in the first excited states(S1)and exhibit dual fluorescence in all the solvents.The calculated intramolecular hydrogen bonds for enol forms can be significantly strengthened in S1 states,which can facilitate the ESIPT processes.In addition,as the polarity of the solvent increases,the degree of hydrogen bond enhancement increases,and the energy barrier in the ESIPT process decreases,which proves that the ESIPT processes are more likely to take place in highly polar solvents.
density functional theoryexcited state intramolecular proton transfersolvent effectspotential energy curves
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