By: Regina Ramazzini

A simple way to create material chemistry that can switch from colored to colorless under defined illumination and can be returned to a colored state using a heat. The material chemistry can be adjusted to control its behavior in response to light or heat resulting in a highly customizable material.

Photoswitch molecules undergo a molecular change induced by light irradiation. Negative photochromes are photoswitches that reside in a conjugated colored form, and upon light irradiation change to a colorless form.  Common photoswitches absorb in the ultraviolet (UV) range and their versatility suffers from the limitations of UV light.  UV light penetrates surfaces poorly and the high energy UV light is damaging too many materials.  Highly tunable, simple to synthesize molecules that photoswitch following irradiation with visible light are very desirable for numerous applications. UCSB researchers have developed a class of materials with absorption spectras that are highly tunable in the visible and near infrared (NIR) wavelengths. Unlike many other photoswitches, these compounds are unresponsive to UV light which allows them to function as switches in systems where UV light is detrimental. In addition, upon switching the material changes from colored to completely clear making them unambiguous tags.  These versatile photoswitches can be adapted to enable switching in liquid or solid materials to facilitate numerous applications.