We are interested in the design and synthesis of stimuli-responsive or “smart” materials, a broad class of materials that respond to triggers such as mechanical force, light, or heat. These types of materials are important because they change their chemical and/or physical properties based on their environment, without the need for external additives. Thermochromic materials have a wide range of practical applications, particularly with regard to fabrics/coatings, devices, and industrial packaging, where the temperature of a substance needs to be tracked. For example, one can envision camouflage combat uniforms that adapt to different temperatures or terrains during war (e.g., desert vs. jungle), reducing the amount of equipment soldiers need to carry. We recently developed the first examples of thermoluminescent borafluorenium ions, which are air-stable and selectively emit across the visible spectrum under temperature control.