Phase transitions in poly (N-isopropylacrylamide)(PNIPAM) covalently labeled with a 2- naphthol were examined by steady-state and time-resolved spectroscopy. 2-Naphthol undergoes excited-state proton transfer (ESPT) at a rate that is dependent upon water concentration in aqueous solvent systems. Upon conversion to the phase-separated state in naphthol-labeled PNIPAM, the efficiency of excited-state proton transfer diminished, ...