Photochromics change from clear when indoors to color when outdoors. Specifically, Photochromics change color in response to UV light, usually from the sun or a black light.
Photochromic behavior can be either reversible or irreversible.
Reversible Photochromics transform from clear to color by changing their chemical structure after absorbing UV light, usually from the sun or a UV light. The UV light causes the Photochromics to absorb color (like a dye), and then change back to clear when the UV source is removed. They can cycle thousands of times depending upon the application. They can also change from one color to a different color by combination with a permanent pigment. When the UV light source is removed, the dye changes back to clear. The number of cycles is dictated by the matrix embedding the photochromic dye. They can also change from one color to a different color by combination with a permanent color.
Standard SpotSee Photochromic Ink will change from clear to color when activated by UV light. We also have an irreversible solvent-based screen ink/label that permanently changes from clear to color after exposure to ultraviolet light.
Photochromic Masterbatch in pellet form can be dosed through injection into molded-plastic items, or into plastic extrusion. The strength of the color change will increase as the plastic thickness increases.
Reversible Photochromics are also found in novelty applications such as tee shirts, toys, cosmetics, nail varnish, ophthalmic and sunglass lenses, footwear, packaging, glassware, ceramics, plastics, security, and industrial applications.
Photochromic Dyes generate dynamic, reversible color change under the sunlight or UV light in the range of 300 to 360 nanometers. When placed into sunlight or UV rays, the molecular structure changes allowing the photochromic compound to turn into a darker color. The effect is reversed when the light source fades. The speed at which the dyes fade back to become colorless depends on the ambient temperature and chemical structure of the dye.
Photochromics are available in the following formats:
- Dyes for direct use in materials able to solubilize them
- Slurries microencapsulated for use in aqueous systems
- Powders microencapsulated for use in non-aqueous systems where protection is required
- Inks for printing onto papers, plastics, and textiles
- Labels used on finished products
- Masterbatch for addition to plastic molding and extrusion
SpotSee Photochromic Inks have an ultraviolet color change response usually from the sun or a black light. Photochromic Dyes can be applied to fabrics through conventional printing and dyeing methods. For example, when textile ink is printing onto clothing, the inks are effectively colorless indoors and turn into vibrant colors outdoors. When brought back inside, the inks become clear again. The inks become intensely colored after only 15 seconds in direct sunshine and return to clear after about 5 minutes indoors. Perfect for textiles and other applications where there is a period of exposure followed by non-exposure to UV light.
A wide range of Reversible Photochromic Products, from raw materials to finished inks, powders, dyes and finished products is available. A Photochromic material can be custom synthesized or formulated specifically for your application, including a color to color change. Please let us know if we can be of assistance in creating your custom product!
Spiropyrans and Spirooxazines
The spiro form of an oxazine is a colorless Leuco Dye. The conjugated system of the oxazine and another aromatic part of the molecule is separated by a sp³-hybridized “spiro” carbon. After irradiation with UV light, the bond between the spiro-carbon and the oxazine breaks, the ring opens, the spiro carbon achieves sp² hybridization and becomes planar. Next, the aromatic group rotates, aligns its π-orbitals with the rest of the molecule. Finally, a conjugated system forms with ability to absorb photons of visible light, and therefore appear colorful. When the UV source is removed, the molecules gradually relax to their ground state, the carbon-oxygen bond reforms, the spiro-carbon becomes sp³ hybridized again, and the molecule returns to its colorless state.
This class of photochromes are thermodynamically unstable in one form and revert to the stable form in the dark unless cooled to low temperatures. Their lifetime can also be affected by exposure to UV light. Like most organic dyes, they are susceptible to degradation by oxygen and free radicals. Incorporation of dyes into a polymer matrix, adding a stabilizer, or providing a barrier to oxygen and chemicals prolongs their lifetime.