Photophysical And Self-assembly Properties Of Photochromic Spiropyran/Spirooxazine And Platinum (?) Derivatives

A photochromic compound is a chemical that absorbs light energy at a certain wavelength and transforms in two states which have different electron absorption spectra.UV illumination induces the transition of spiropyran/spirooxazine compounds from closed form to open form named merocyanine,resulting in the conversion of the molecular conformation from approximately orthogonal to planar with a larger conjugation system,and from hydrophobic electroneutral to hydrophilic ionic.The molecular planarization and the transformation of amphiphilicity make spiropyran/spirooxazine compounds good elements for the construction of stimuliresponsive assemblies.Pt(?)has a d8-unsaturated electronic structure and a planar quadrilateral configuration,when introducing a wide variety of ligands,they can exhibit rich photophysical properties.At the same time,the planar quadrilateral structure is easy to form Pt-Pt interactions and ?-? stacking,which is conducive to the construction of supramolecular assemblies.Based on the above basis,we designed and synthesized a series of photochromic spiropyran/spirooxazine and metal Pt(?)derivatives and explored their photophysical and solution assembly properties,expecting to reach the following vision: The photophysical properties would be modified by changing the molecular design through changes in electronegativity of the molecular groups.The kinetics of the bleaching reaction would be further regulated by the change in the electronegativity of the molecular group after the application of UV light to trigger the photochromic reaction.The hydrophilicity and conformational changes brought by spiropyran/spirooxazine derivatives before and after the transformation,would be capable of changing the intermolecular forces.Together with the metal interaction among the metal Pt(?),by modulating the polarity and protonation of the solvent,would allow us to probe the UVlight-modulated molecular assembly behavior.Therefore,selecting photochromic spiropyran/spirooxazine and metal Pt(?)derivatives as substrates,by adjusting the molecular design,UV illumination and solvent polarity,we expect to achieve regular luminescence behavior and bleaching reaction,as well as the construction of stimuliresponsive assemblies.This has important implications for the development of photochromic compounds and metal Pt(?)complexes in the exploration of photophysical properties and smart materials.In this thesis,we designed and synthesized a series of compounds containing spiropyran/spirooxazine and metal Pt(?)as structural motifs,constructded UV lightresponsive supramolecular assemblies by non-covalent interactions,and explored the basic photophysical properties,kinetics of photochromic bleaching reactions,and solution self-assembly process of the compounds based on the construction of spiropyran/spirooxazine derivative assemblies.Firstly,hydrophobic alkyl chains with different lengths were introduced into the spiropyran derivatives through different linkage groups.The approximate orthogonal conformation of the closed structure and longer spiro C-O bonds were visualized by the crystal structure,which is more favorable for the photochromic reaction.By changing the linkage groups in the molecule,the bleaching reaction rate was changed.By increasing the length of alkyl chains,a regular change in the shape of the merocyanine assembly from nanospheres to nanosheets was achieved in solution,while the results of NCI further demonstrated the existence of ?-? stacking in the merocyanine part and the hydrophobic interactions in the alkyl chain part in the assembly process.This work was not only the first to demonstrate the existence of non-covalent interaction in the H-aggregation process of spiropyran derivatives by NCI,but also provided a reference for the construction of assembly motifs in molecular assemblies.Secondly,hydrophilic triethylene glycol chains replacing hydrophobic alkyl chains were introduced into the spiropyran derivatives.Changing the volume and amphiphilicity of the molecule could change the rate of the bleaching reaction.In water-containing polar solvents,the solvent-induced spontaneous ring-opening process was realized by the stabilization of open form through polar solvent water,which facilitated the conversion of the closed form to the open form.In contrast,in hydrophobic solvents,the aggregation behavior of the open and closed forms was realized separately,and the self-assembly behavior of the open form slowed down the bleaching reaction.The size of the assembled structure was altered by changing the molecular structure,changing the polarity of the solvent,and applying UV light.This work realized the aggregation of closed and open form of spiropyran derivatives in solution,which provided ideas and opportunities for the design and preparation of controllable functionalized self-assembled materials.Thirdly,based on the work in the previous two chapters,we introduced the more planar Pt(?)to exploit the d8 electron configuration and planar tetragonal configuration,and to obtain richer photophysical properties and self-assembly behavior.We have synthesized a set of Pt(?)complexes with spirooxazine/spiropyran as ligands and constructed a series of assemblies in solution.The MLCT luminescence was achieved by introducing alkynylbenzene and constructing a more planar complex containing a metal ring,which was sensitized by the photochromic reaction of spirooxazine to enhance the MLCT luminescence and achieve intramolecular energy transfer.All the complexes could achieve assembly behavior,and the application of UV light brought changes to the assembly of the complexes.This work achieved richer photophysical properties by introducing Pt(?),and discovered the intramolecular photosensitization phenomenon.As for the Pt(?)complexes containing photochromic spirooxazine/spiropyran ligands,the investigation of the self-assembly behavior in solutions have been added to the previous work of our group,which broadened the research ideas and also provided a reference for the development of Pt(?)complexes.In conclusion,we integrated specific structural extended framework based on photochromic spiropyran/spirooxazine.Among them,the introduction of alkyl chains brought hydrophobic interactions,the introduction of triethylene glycol brought hydrophilic interactions,and the introduction of Pt(?)brought metal interactions.These intermolecular interactions,together with the ?-? stacking from merocyanine,have driven the achieving of a series of supramolecular assemblies.Through molecular design,we have changed the photophysical and photochromic properties of the compounds and also achieved the adjustment of the assembly morphology.And the introduction of Pt(?)realized the intramolecular sensitization between photochromism and MLCT luminescence.The research in this thesis realized regular luminescence behavior and bleaching reaction,as well as the construction of stimuli-responsive assemblies through rational molecular design,application of UV light and reasonable solvent selection,which are important for the development of photochromic compounds and metal Pt(?)complexes in the exploration of photophysical properties and smart materials.