In present invention, various embodiments provide a photothermotropic composite film. The composite film comprises a matrix and one or more nanostructures comprising a metal oxide semiconductor which is configured to convert radiant energy to thermal energy. The matrix has a property which is changeable based on the thermal energy received by the matrix from the metal oxide semiconductor. In a preferred embodiment, hybridization of the poly(N-isopropylacrylamide) (PNIPAM) hydrogel and antimony-tin oxide (ATO) is provided as the composite film. In this film, the ATO absorbs at near-infrared (NIR) region and acts as nanoheater to induce the optical switching of the hydrogel. The behaviour of this composite film can be used as a new generation of autonomous passive smart windows for climate-adaptable solar modulation.