New Light on the Ring-Chain Equilibrium of a Hydrogen-Bonded Supramolecular Polymer Based on a Photochromic Dithienylethene Unit and its Energy-Transfer Properties as a Storage Material

A novel, bifunctional, quadruple hydrogen‐bonding ureido‐pyrimidinone (UPy) unit bridged by photochromic dithienylethene (1) has been synthesized, which affords linear assemblies in solution and undergoes concentration‐dependent ring‐opening polymerization. The two UPy functional groups of 1 can dimerize intramolecularly to form a cyclic monomer with the two thienyl rings fixed in a parallel conformation, which prohibits its photocyclization. We exploited the photochemical reactivity and resonance difference of the linker of the bis‐UPy derivative as well as using the more typical 1H NMR, DOSY, and Ubbelohde viscometry methods to investigate for the first time the ring–chain polymerization mechanism. Moreover, we fabricated a mixed polymer film with a fluorescent dye noncovalently endcapping the linear photochromic assemblies through quadruple hydrogen bonds, which showed nondestructive fluorescent read‐out ability for data storage by fluorescence resonance energy transfer (FRET) from the fluorescent dye to the closed form of the diarylethene. Ring–chain equilibria! The ring–chain equilibrium of a hydrogen‐bonded supramolecular polymer bridged by a photochromic dithienylethene unit has been investigated for the first time by photochemical and NMR methods (see figure). A mixed film with a fluorescent dye noncovalently endcapping the linear photochromic assemblies by quadruple hydrogen bonds presents a fluorescent switch with nondestructive readout ability for data storage.