| Fluorescence spectroscopy,1H NMR spectroscopy and quantum chemical calculations were used to investigate the interactions of benzo[6]urils with polycyclic aromatic hydrocarbons acting as the guest molecules.The fluorescence emission of the host was decreased upon the addition of an increasing amount of the guest molecules providing the association constants in the range of 8×102-7.5×104 L·mol-1via non-linear curve fitting and confirmed the formation of host–guest complexes in a1:1 ratio with Job's plot analysis.In addition,the 1H NMR spectra also supported the formation of the interaction complexes with changes of chemical shifts of the protons on aromatic protons in the presence of host molecules.The results of calculation chemistry provided the structures of the encapsulation complexes,and the driving force was attributed to the formation of hydrogen bonds between the benzo[6]urils and the guest molecules.The unique properties of ECL of methyl-substituted benzo[6]uril 1 was found,and the ECL response of macrocycle 1 to the addition polycyclic aromatic hydrocarbons was observed.It was found that benzo[6]uril 1 exhibited electrochemiluminescence at+1.1v with an oxidation peak,and the luminescence mechanism depended on the concentration of hydroxide ions in the solution.Unexpectedly,the luminescence was quenched completely by the addition of a small amount(10-13 mol·L-1)of the guest molecules,except for triphenylene,with a surprising increase in the diffuse current,which could be the result of the addition of the electron-rich polycyclic aromatic hydrocarbon guest molecules restraining the formation of the excited state of benzo[6]uril?1*?.In the case of triphenylene,a concentration-dependent response for the ECL was observed and the ECL intensity of benzo[6]uril 1 increased upon decreasing the concentration of triphenylene,and the non-linear relationship can be fitted by the intensity changes.Therefore,it was foreseeable that benzo[6]uril 1 could be applied as a potential material with a non-linear response of ECL.Based on the host-guest interactions of paraquat and diquat with benzo[6]uril 1,an ECL sensor has been developed,and the results exhibited a quenching effect of the guests on the luminescence intensity of benzo[6]uril 1.The dropped intensity was used for the quantitative detection in the concentration range from 1.0 mM to 1.0 uM for paraquat,and 10.0 mM to 1.0 uM for diquat with good recoveries and relative standard deviations.Luminol,a classical luminophore,was employed to achieve the competition with the bipyridyl herbicides for interactions of benzo[6]uril 1,which was also been applied for quantitative response for the guests. |
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