Synthesis Of Coumarin-based Phytochromes And Self-assembly Of Coumarin-functionalized Gold Nanoparticles

Light-induced reversible self-assembly(LIRSA)has recently attracted considerable attention because of the advantages of easy,economical,and efficient control of higher-order domain structures for a wide range of practical applications.Theoretically,most self-assembled nanostructures that respond to light in a reversible manner do so by either photoisomerization or photodimerization through the introduction of chromophores on the nanoparticle(NP)surface.Unlike photoisomerization,the photodimerization process and its reverse do not significantly alter the atomic positions of the aromatic system.Each monomer unit remains essentially intact,and the photodimers formed by polycyclic aromatic hydrocarbons can be photodissociated to generate the original monomers.It is therefore highly desirable to explore a tolerant physical and chemical micro-environment for the delicate LIRSA system to realize the significantly reversible self-assembly of modified NPs via photodimerization and photocleavage of coumarin groups.The weakly toxic dye coumarin and its derivatives are found in many plants and constitute an important example of reversible photodimerization.Despite the use of coumarin derivatives in a wide variety of fields,their potential application in the LIRSA of NPs to achieve good reversibility and high switching rates has been rarely investigated,possibly because of complex and sensitive issues.In this work,a thiolated coumarin derivative 7-(1 1-mercaptoundecanuxy)coumarin(1)was synthesized by a four-step synthesis.AuNPs with a mean size of 7.6 nm were prepared using a modification of a procedure described in the literature.The design of colloidal coumarin-functionalized AuNPs capable of reversible self-assembly based on the photolysis of coumarin in response to light irradiation was reported.Facilitated by coumarin groups,light irradiation at 365 nm triggers the stable assembly of monodisperse AuNPs;the resulting self-assembly system can be disassembled back to the disassembled state by a relatively short exposure to benign UV light.Maintaining an appropriate concentration of coumarin ligand on the surface of NPs and the suppression of the anti-configuration dimers(anti-CDs)by THF during irradiation are key for successful LIRSA.A nucleophilic THF as a moderately polar solvent was used to disperse coumarin-functionalized AuNPs(1-AuNPs).More importantly,THF was used as an electron donor to yield the charge-separated coumarin singlet excimer,ensuring e?ective photocleavage for the rapid disassembly of 1-AuNPs,The LIRSA of the 1-AuNPs/THF system can be repeated with full recovery for 4 cycles,making them promising materials for light-driven actuating applications.