Molecular Swich

1 is a three state photochromic compound that responds to chemical and optical inputs to produce optical outputs. The colorless spiropyran state (SP) switches to the purple merocyanine form (ME) on irradiation with UV light. Alternatively, SP switches to the yellow-green protonated merocyanine (MEH) on acidification. The colored form ME and MEH return to the colorless state SP when they are irradiated with visible light. Similarly, ME returns to the SP state when stored in the dark. The addition of acid to ME produces MEH, and the treatment of MEH with base restores ME. The studies of the molecular switch which applied these properties have been actively carried out.