Photoswitchable Quadruple Hydrogen Bond Based On Reversible “Photolocking” Strategy And Its Application In Photocontrollable Self-assembly

The reversible stimuli-responsiveness has enabled multiple hydrogen bonding motif to play a fundamental role in the construction of multiple H-bonded self-assembled systems and materials with attracting structural and functional photocontrollability.Among various stimuli,light has been widely used in the construction of photoresponsive H-bonded self-assembled systems and materials for the unique clean and spatiotemporal features.However,efficient approach to construct photoswitchale multiple H-bonding motifs remains lacking currently,which limits the development of photoresponsive multiple H-bonding assemblies and materials.Therefore,exploring new strategies to construct novel photoresponsive multiple H-bonded motifs with significant photoswitchable association constants,is of great significance for the construction of controllable supramolecular self-assemblies and functional supramolecular materials.In this thesis,we describe a unique reversible“photolocking”strategy for the photoswitchable control of quadruple H-bonding interactions on the basis of modifying the urea side of the ureidopyrimidinone（UPy）module with an ortho-ester substituted azobenzene unit as the“photo-lock”.Upon light irradiation,the obtained photoswitchable motif（Azo-UPy）is capable of unlocking/locking the partial H-bonding sites（two N-H groups of urea moiety）of the UPy unit,which enables Azo-UPy to exhibit photoswitchable H-bonded dimerization behavior.Experimental investigations reveal that the pristine E-Azo-UPy is existed as monomer,while the photoirradiated Z-Azo-UPy prefers to form quadruple H-bonded dimer with an apparent dimerization constant of K_dim=1.2×10⁵ M^-1.Meanwhile,the Azo-UPy is able to reversibly form the quadruple H-bonded hetero-dimer with the nonphotoactive（UPy-1）₂ dimer upon light irradiation.Furthermore,unique photoregulable macromolecular aggregation is achieved by photocontrolling the“on/off”states of dimerization behavior between the Azo-UPy units attached to the polymer chains.In addition,the Azo-UPy is also capable of acting as chain cappers to photoregulate the degree of polymerization of quadruple H-bonded supramolecular polymer fabricated from nonphotoactive UPy monomer.In light of the widespread application of multiple H-bonding motifs in supramolecular chemistry and materials science,together with the fact that there is no special requirement for the core structure while implementation,such"photolocking"strategy is expectable to be widely used in the rational design and construction of other photoswitchable multiple H-bonding modules.