Reverse Hofmann-Type Spin-Crossover Compound Showing a Multichannel Controllable Color Change in an Ambient Environment

Materials that demonstrate a multichannel controllable color change in response to external stimuli are fascinating for their potential applications in sensoring and displaying devices. Herein we report a Fe-II spin-crossover (SCO) compound that exhibits both solvatochromism and thermochromism under an ambient environment. This Hofmann-type compound possesses two different pores where the solvent guests can be removed in a two-step process. Because the loss of solvent guests modifies the spin state of magnetic centers, an unusual yellow-red-yellow two-step color change of crystals was detected. Moreover, because of the strong cooperativity of the spin centers, a dramatic red-to-yellow color change of crystals in response to a minute thermal perturbation around 303 K is triggered by an abrupt spin transition of the metal centers. The multichannel controllable dramatic color change demonstrated in the present compound highlights the sensoring and displaying roles of SCO materials.