Shining New Light on the Spiropyran Photoswitch: A Photocage Decides between cis- trans or Spiro-Merocyanine Isomerization.

Photochromic molecules from the spiropyran family are known to undergo light-induced interconversion between the colorless spiro- and the colored merocyanine forms. Here, we show for the first time that small structural modifications open up for an additional photoisomerization mode: reversible cis- trans isomerization of the merocyanine. Moreover, the introduction of a photocage allows for light-activated switching between the two modes.