Phase transition dynamics of fluorescent-labeled poly(N-isopropylacrylamide) in aqueous solution as revealed by time-resolved spectroscopy combined with a laser T-jump technique

In order to clarify the dynamics of phase transition from coiled states to globular states in a thermo-responsive polymer, poly(N-isopropylacrylamide) (PNIPAM), we developed a method of dynamic (time-resolved) fluorescence spectroscopy combined with a laser T-jump technique. Using this, we revealed the phase transition dynamics of fluorescent-labeled PNIPAM in aqueous solutions. The phase transition dynamics was reflected in a dynamic Stokes shift of a TICT fluorescence of the probe. The time constant of the phase transition (τ) was determined to be 35 μs, irrespective of the sample concentration studied (0.1–1.0 wt.%), and this was longer than that predicted from the diffusion–collision model.