Photochromic molecules are designed in order to display photocontrolled DNA-binding. Often, only one of the two isomeric forms binds to DNA, and several of these derivatives only bind to DNA after protonation. This may be useful in the development of photoactivated anticancer drugs. Other derivatives bind to DNA in both forms, but with different binding modes. This phenomenon has been used to achieve enantioselective cyclization of DNA-bound DTE derivatives.