Quinone-derived carbon-dot photoinitiation regulates network mechanics and thermoresponsive phase separation in P(NIPAM-co-AAm) hydrogels

The macroscopic response of a thermoresponsive hydrogel depends on how its network translates molecular dehydration into mesoscale phase separation, yet the role of photoinitiating chemistry in this multiscale process is rarely considered. Here, quinone-derived carbon dots (Q-CDs), paired with N,N,N',N'-tetramethylethylenediamine (TEMED), were used as a photoinitiating system for thermoresponsive poly(N-isopropylacrylamide-co-acrylamide) hydrogels, with the fluorescent Q-CDs retained in the resulting network. Compared with an Irgacure 2959-initiated reference, the Q-CD/TEMED-initiated hydrogel exhibited a finer porous morphology and a markedly enhanced elastic response. Differential scanning calorimetry revealed essentially unchanged endothermic transition temperatures near 49 °C, whereas the optically determined phase-transition temperature decreased from approximately 58 to 45 °C; the Q-CD/TEMED-derived hydrogel also exhibited a narrower calorimetric heating-cooling hysteresis. This divergence suggests that Q-CD-mediated network formation influences the mesoscale development of phase-separated domains more strongly than the underlying polymer-water dehydration transition. The transparent-to-opaque response remained reproducible over 100 thermal cycles, while the detected Q-CD fluorescence decreased across the same transition region. These findings extend carbon-dot photoinitiation beyond hydrogel synthesis to a network-design strategy for regulating how molecular dehydration develops into mesoscale phase separation and macroscopic optical response.