Tunable Single‐Molecule White‐Light Emission in Stimuli‐Responsive Hydrogel

White‐light emitting materials based on single‐molecules are of great interest owing to the simple fabrication process and good stability of such materials. However, among limited reports on single‐molecule white light‐emitting materials, the majority of systems are based on organic solvents. Here, a single‐molecule white‐light emitting hydrogel is prepared through the combination of a protonation sensitive fluorophore with a temperature sensitive hydrogel. The mechanism of this system is based on adjusting the ratio of protonated and deprotonated fluorophores through the thermally controllable hydrophobic property of the hydrogel internal microstructure. The fluorophore emits intense blue and yellow emission in its protonated and deprotonated states, respectively; hence, the luminescence of the hydrogel changes color as a function of temperature and [H+], achieving a white color under certain conditions. On the basis of these results, a multicolor light‐emitting device (LED) and a white‐light LED are realized by placing the prepared hydrogel on a conductive substrate over a UV LED chip.