Red-shifted Ultraviolet Absorption Peak in ESOF Attributed to Furan Group Incorporation

Compared to ESO, the unsaturated double bonds in the furan group of ESOF can undergo 'ππ' transitions, resulting in a red-shift of the ultraviolet absorption peak. This can be confirmed through ultraviolet-visible spectroscopy tests, indicating the incorporation of the furan group into the main chain of ESO.