Colorimetric Recording of Thermal Conditions on Polymeric Inverse Opals

Recording thermal conditions, i.e., temperature and time, is of great importance for various applications. Although thermometers can measure temperature and record its temporal change with electronic devices, they are nondisposable and not patch‐type, restricting their uses. Here, photonic films are designed that record thermal condition through irreversible structural deformation and intuitively report it with color patterns. The photonic films are inverse opals made of negative photoresist on a solid support, where the cross‐linking density of the photoresist is regioselectively adjusted. The photonic films show a gradual blueshift of structural color upon heating due to anisotropic compression of the inverse opal, of which the rate depends on temperature and cross‐linking density. For single cross‐linking density, thermal input is quantified from the color change in the form of coupled temperature and time. With multiple cross‐linking densities in a single film, the multicolor pattern is developed, from which the temperature and time are decoupled and separately estimated for isothermal condition. Thermal recorders are designed in a patch format using inverse opals made of negative photoresist. For thermal input, the inverse opals are irreversibly compressed along the thickness direction, leading to a blueshift of the photonic stopband. With regioselective control of UV dose, the inverse opals turn to multicolor patterns whose blueshifts decouple the temperature and time for isothermal heating.