Theoretical Investigation On Fluorescence Detection Mechanism Of Several Small Molecules By Covalent Organic Frameworks

Fluorescence detection has many unique advantages in sensing small molecules.New luminescent materials are of great significance for the application of fluorescence dection.Based on the hydrogen bond,this paper explores the application prospects of luminescent covalent organic frameworks(COFs)in several small molecules fluorescent detection.The following study method is used.Firstly,intercept the representative consensus motifs from the crystal structure of luminescent COFs.Next,screen the COF-molecular hydrogen bond complexes based on energy.Finally,analyze the electron transition process hydrogen bond complexes qualitatively and quantitatively,ascertain the possibility of applying the luminescent COFs in small molecules detection,and guide the design of fluorescence detectors theoretically.The application prospect of PPy-COF for fluorescence dection of nitro-aromatic explosives is explored.Hydrogen bond complex has formed between PPy-COF and nitro-aromatic explosives and lead significant change of luminescence mechanism;The hydrogen bonds of complex have enhanced in electronic excited state;The fluorescence rate constant has reduced and internal conversion rate constant has increased significantly and induces fluorescence quenching.The feasibility has been predicted theoretically of the application of PPy-COF in the nitro-aromatic explosives fluorescence dectionThe application potential of PPy-COF in ammonia fluorescence detection is investigated.Ammonia can form a hydrogen bond complex with PPy-COF,and change the frontier molecular orbitals and electronic configurations;By analyzing hydrogen bonds behavior of hydrogen bond complex in excited state,hydrogen bond enhancement is found;According to the calculation results of fluorescence rate constant and internal conversion rate constant,fluorescence quenching of PPy-COF caused by ammonia is analyzed quantitatively.PPy-COF has potential as ammonia fluorescence detection materialThe effect of formaldehyde on the fluorescence properties of Bth-Dha COF was investigated.Formaldehyde will change the frontier molecular orbitals charge distribution and electronic configurations of Bth-Dha COF,and cause the altering of luminescence mechanism;The change of hydrogen bonds geometry,~1H-NMR chemical shift and hydrogen bond donor and acceptor vibration frequency of the hydrogen bond complex in the excited state indicates that the hydrogen bond is enhanced under the excited state;The quantitative analysis of the electronic transition process shows that formaldehyde will cause fluorescence quenching of Bth-Dha COF.Explain that Bth-Dha COF is a potential formaldehyde fluorescence detection material.Fluorescent COFs can form hydrogen bond complexes with small molecules.In the excited state,the behavior of hydrogen bonds in the complexes will affect energy levels,affect the transition process,and change the luminescence performance.In the hydrogen bond complex systems selected in this paper,hydrogen bond enhancement occurs in the excited state,which is not conducive to the radiative transition,but beneficial to the non-radiative transition,and finally causes fluorescence quenching of COFs.