Multi-stimuli responsive poly(N-isopropyl-co-tetraphenylethene) acrylamide copolymer mediating AIEgens by controllable tannic acid

Copolymerization of N-isopropylacrylamide (NIPAM) and tetraphenylethene (TPE) acrylamide monomers produced aggregation-induced emission (AIE) active copolymers P1, P2, and P3 with relatively lower molecular weights (6000). Like poly-N-isopropylacrylamide (p-NIPAM), an aqueous solution of copolymers (P1-P3) responds to temperature and undergoes a change in fluorescence intensity due to conformational transition (swelling/shrinking) below and above their lower critical solution temperature (LCST), respectively. The LCST of p-NIPAM (32 °C) shifted downward upon the incorporation of TPE in the copolymer chains depending on the concentration of TPE. Compared to P1, the fluorescence response increased to a five-fold enhancement with increasing concentrations of tannic acid (TA) owe to the form of the P1-TA complex. Furthermore, the P1-TA complex showed a surprising change in fluorescence response under the effect of temperature and pH value. The conformational transitions of P1-TA were also studied by dynamic light scattering (DLS). DLS measurements for the P1-TA complex justified its fluorescence response based on particle size at different concentrations and pH value. Such stimuli-responsive AIE-active copolymers find potential applications in drug delivery systems for monitoring loading and release processes by fluorescence.