Photochromic Hydrazone Switches with Extremely Long Thermal Half-Lives

A family of easily accessible light-activated hydrazone switches has been developed having thermal half-lives of up to 2700 years! Structure–property analysis shows that replacing the rotor pyridyl group of our typical hydrazone switch with a phenyl one leads to the long-lived negative photochromic compounds. The switching properties of the hydrazones in both toluene and DMSO were assessed offering insights into the kinetics and thermodynamics of the switching process.