Self-assembly and Mechanism Research of Pyridine-based Organic Materials

Author:Wang Hai Yan

Supervisor:zhou hong ping kong lin


Degree Year:2019





Molecular self-assembly refers to the spontaneous aggregation of molecules through interaction forces to form specific morphologies and structures.Distinguished from single molecule,self-assembled molecules deliver unique properties and functions,witnessing broader application prospects.Due to their unique photoelectric properties,organic π-conjugated molecules have attracted much attention because they can compose optoelectronic materials with novel structures and excellent properties through self-assembly by means of weak intermolecular interactions.Of note,appropriate self-assembly units and conditional control are very important for the properties of self-assembled materials.Quantum chemistry method can obtain the mechanism of self-assembly and external environmental impact factors through the studies of chemical bonds and intermolecular forces,which can guide experiments and thus broaden research ideas.In this dissertation,several pyridine-based organic materials were designed and synthesized,and their optical properties,practical applications in ion recognition and biological imaging were studied.According to the experimental results,Various model algorithms for multiple object systems were established and Natural Bond Orbital(NBO)atomic charges,Wiberg bond index(WBI),HOMO-LUMO gaps and complexation energies were studied by density functional theory(DFT)using BP86,B31YP,M060X and MP2 theoretical methods and 6-31g(d,p),6-31g(d),6-311++g(d,p),cc-pvtz and lanl2dz basis sets.Combining experiment with theory,the self-assembly mechanism of pyridine-based organic materials,the regulation mechanism of optical properties and the effect of external environments on the morphology and optical properties of self-assembly materials were explored.The main research contents are as follows.1.Recognition mechanism of coumarin-based pyridine derivatives for Hg2+ and Cu2+Two novel coumarin-based pyridine probes,named L1 and L2,were designed and synthesized.L1 contained two pyridine groups,which can recognize Hg2+(turn-on)and Cu2+(turn-off)in aqueous solution,and L1-Hg2+single crystal was obtained by self-assembly in acetonitrile solution.L2 contained one pyridine group and can specifically recognize Hg2+(turn-on)in methanol-H2O mixed solutions,but it can not recognize Cu2+.Through theoretical calculation,the optimum coordination site of L1 and Hg2+ was determined to be N atoms of pyridine groups,and the optimal coordination number for metal center was 5,which was consistent with the self-assembled single crystal structure.Modeling and calculating based on single crystal structure of L1-Hg2+,the five-coordination models of L1 and Cu2+,as well as that of L2 and Hg2+ were constructed.Additionally,the reason why L2 could not recognize Cu2+ was analyzed.Meanwhile,by virtue of the comparison of the calculated results of monomer and dimer models,it was revealed that the self-assembly models between L1/L2 and the identified ions were mainly monomers.2.Recognition,application and mechanisms of tripyndine-based derivatives for Hg2+Tripyridine-based derivative TPI with good water solubility,multi-ligand site hairpin structure and methoxypyridine units was designed and synthesized,which can detect Hg2+(detection limit is 1.38 × 10.7 mol·L-1)in simulated water samples and were made into test paper.Theoretical calculations results showed that intramolecular photoinduced electron transfer(PET)resulting from the coordination of TPI with Hg2+ led to red shift of emission peaks,which was the main reason why TPI had good naked eye recognition ability for Hg2+.By means of NMR titration and mass spectrometry analysis,it was unveiled that Hg2+ mainly coordinated with methoxypyridine groups,and the theoretical calculation results of different coordination models further showed the rationality of this coordination model.3.Preparation,self-assembly mechanism and optical properties of monomer/assembly aggregates of tripyridine-based derivativesPYTPY,2,2’:6’,2’-tripyridine-based derivative with A-π-A structure was designed and synthesized,and its crystal structure was obtained.The relationship between orientation growth and aggregation morphology of PYTPY and changes in optical properties induced by self-assembly were studied by calculating extraction models from single crystal structure.The calculation results showed that PYTPY had good planarity and high electron delocalization due to its π-conjugated structure,and intermolecular hydrogen bonding was the main force for PYTPY to form one-dimensional and two-dimensional stacking structures and the weak π-πinteraction propels PYTPY to form three-dimensional aggregates.In the THF-H2O mixed solvent,the weak force ratio of PYTPY dimer in three dimensions was 1.00:0.17:0.60,and self-assembly structure tended to form two-dimensional structure.Moreover,electron transitions occurred both before and after self-assembly.The above calculation results were in good agreement with the experimental results,which further proved the reliability of the modeling and calculation methods.4.Self-assembly and stimulus responsibility for optical properties of tripyridine-based derivatives PYTPYThe effects of external environments(including anions,metal ions,acidity and alkalinity)on the self-assembly and electronic transition of PYTPY were studied by combining experiment with theory.The results showed that anions and sodium ions had little influence on the self-assembly morphology of PYTPY.With weak acid added,the ratio of weak interaction force in three dimensions of PYTPY dimer was 1.00:0.83:0.96,so its self-assembled morphology tended to form three-dimensional structure,and the red shift of absorption and emission wavelength was observed.When the acidity increased,the weak interaction force ratio in three dimensions of PYTPY dimer was 2.71:3.66:1.00,which tended to form a one-dimensional structure,and the electron-absorbing ability increased,resulting in the change of the intrinsic absorption peak of PYTPY and strong photoresponsiveness.Induced by Ag+,the weak interaction force ratio in three dimensions of PYTPY dimer was 0.98:1.00:0.84,which tended to form three-dimensional structure in micro-scale and one-dimensional linear structure self-assembled from the zero-dimensional nanostructures in macro-scale.The ultraviolet-visible absorption spectra of the system showed red shift,and there was always intramolecular charge transfer(ICT).