The photochemical properties of photochromic materials change with exposure to different wavelengths of light due to the nature of their molecular structure and the energy levels associated with their electrons. Photochromic materials are characterized by their ability to reversibly change color when exposed to ultraviolet UV or visible light. This color change is a result of the absorption of photons, which causes a change in the electronic state of the photochromic molecules.When a photochromic material is exposed to a specific wavelength of light, the energy of the photons in that light is absorbed by the photochromic molecules. This absorption of energy causes the electrons in the molecules to transition from their ground state to an excited state. The energy required for this transition is specific to the molecular structure of the photochromic material and the wavelength of the light.Different wavelengths of light have different energies associated with their photons. When a photochromic material is exposed to a wavelength of light that matches the energy required for an electronic transition, the material will undergo a photochemical reaction, leading to a change in its color or optical properties. This change is reversible, and the material will return to its original state when exposed to a different wavelength of light or when the light source is removed.For example, some photochromic materials may change from a colorless state to a colored state when exposed to UV light, and then return to their colorless state when exposed to visible light. This is due to the different energies associated with the photons in UV and visible light, which cause different electronic transitions in the photochromic molecules.In summary, the photochemical properties of photochromic materials change with exposure to different wavelengths of light due to the specific energy levels associated with their molecular structure and the absorption of photons. This leads to reversible changes in the color or optical properties of the material, allowing for various applications such as smart windows, sunglasses, and optical data storage.