All‐Optical Fine‐Tuning of Absorption Band of Diarylethene with Photochromic Acid‐Generating Spiropyran

By taking advantage of pKa difference for the isomers of a spiropyran (MC and SP), a continuous and reversible shift of the absorption band of the closed form of diarylethene (C) for 30 nm is successfully realized only by light irradiation and thermal treatment, i.e., without the addition of any chemical species or the application of any physical contact.