Fluorescent and thermoresponsive tetraphenylethene-based cross-linked poly(N-isopropylacrylamide)s: Synthesis, thermal/AIE properties, and cell viability

Background: The synthesis, thermal properties, and aggregation-induced emission (AIE)-responsive properties of a series of tetraphenylethene (TPE)-based cross-linked poly(N-isopropylacrylamide)s (PNIPAms) consisting of a hydrophilic/thermosensitive NIPAm monomer and AIE-responsive/hydrophobic TPE derivative through reversible addition-fragmentation chain transfer polymerization was investigated in this study. Methods: The AIE effect was investigated in a H2O/THF mixture via photoluminescence intensity measurements, and the polymers showed emission (λem = 485 ± 5 nm). When the water fraction was 90%, the PL intensity was enhanced to the highest value. Significant findings: Polymers P1–P3 showed the low critical solution temperature (LCST) at approximately 33.5, 32.4, and 28.1 °C, respectively, and deformed at P4 and P5. From dynamic light scattering, the hydrodynamic diameters of P0 and P1–P2 at a temperature higher than the LCST decreased from 564.0 to 159.6 nm, 417.4 to 126.7 nm, and 469.4 to 134.5 nm (P0, P1, and P2, respectively), indicating the thermoresponsive property. A MTT assay was used for HepG2 liver cancer cells at a concentration of 2 µg/mL, and all the polymers showed cell viability over 80%. P2 and P3 showed emission in the living HepG2 cells for 96 h of incubation. These findings suggest that the synthesized polymers have potential as drug carriers.