Photochromism of spiropyrans has first been investigated in 1952 by Hirshberg and Fischer.Based on their photoswitching properties,research has been carried out with spiropyrans for applications as molecular logic elements,light-actuated nanovalves and manipulation of in vitro selection processes by light-regulation.Hirshberg already suggested an idea of using the photoswitching process as basis for photochemical erasable memory devices in his early work.More than 30 years later,the use of spiropyrans has been demonstrated for bit-oriented three-dimensional optical data memory systems.Herein,two new alternative synthetic routes to modify biomolecules covalently with spiropyrans are reported: for the first route a spiropyran derivatives was synthesized as a photoswitchable cross-linkers for labeling biomolecular probes;the second route applies a postsynthetic click-type ligation strategy.Peptides,proteins and nucleic acids have been conjugated with spiropyrans in order to endow these biomolecules with the optical switch.