A triple hydrogen-bond dominated fluorescent probe for monitoring the melting transition of polyurethane

Accurately characterizing the phase transition temperatures of polyurethanes (PU) is indispensable in controlling over the material processing and usage conditions yet challenging. Herein, a DDA-AAD-type triple hydrogen-bonded luminescent complex was developed based on 7-methyl-1,8-naphthyridin-2-amine (D-Ny) and 1,3-dipyridin-2-ylurea (A-Py) to serve as a novel fluorescent probe for monitoring the melting transition of PU. The complex exhibited thermoreponsive luminescence in THF, with inflection in fluorescence intensity at the melting temperature of the solvent. Taking advantage of the specific luminescence response to the phase transition of the matrix, the triple H-bonding groups were chemically bonded into a polyurethane (PU) backbone as the dynamic chain extenders. The melting transition of the soft and hard segments were demonstrated respectively in real time in the temperature-dependent PL spectra of the fluorescent probe, offering higher sensitivity than the signal in DSC curve in determining the melting temperature of the hard segment. This study provides a prospective approach to monitor the melting transition of PU using a dynamic temperature-sensitive fluorescent probe.