A multifunctional polyurethane with solid-state and acid-base responsive fluorescent emission

Abstract

A multifunctional fluorescent polyurethane (MFP) with solid-state and acid-base responsive fluorescence emission was reported by bonding 1,5-dihydroxy naphthalene(1,5-DN) into polyurethane backbone. The structure of MFP was confirmed by characterization with 1H NMR, FTIR and UV spectra. The fluorescent emission property and acid-base response behavior of MFP samples were studied on fluorescence spectrophotometer. The structural characterization revealed that 1,5-dihydroxy naphthalene was introduced into the polyurethane chain in the form of chemical bond. The physical entanglement and interactions of polymer chains could limit the strong π-π stacking between 1,5-DN. Therefore, MFP exhibited an obvious fluorescence emission at around 460 nm both in solution and solid state, which indicated that the “aggregation-caused quenching” (ACQ) phenomenon had been successfully eliminated. More interestingly, we found that the MFP solution samples have different fluorescence emission wavelengths in the acid (490 nm, blue-green light) and base (460 nm, blue light) environments, with a maximum displacement of over 30 nm. Meanwhile, the fluorescence intensity in strong base (pH = 11) environment decreased by 89% compared with that in strong acid (pH = 3) environment. Base on the dual feature response behavior, MFP has the potential to be used for double signal detection in strong acid and base environments.