Synthesis Of Tripod BODIPY Via Aromatic Nucleophilic Substitution Of Amines At Low Temperature And Quantum Chemistry Calculation

The structure of BODIPY has been developed rapidly due to its excellent properties.In this paper,bis-substituted intermediate a,prepared from cyanuric chloride,was used to conduct condensation with 2,4-dimethylpyrrole and oxidation in one pot.The nucleophilic substitution with amines(diethylamine and aniline)and complexation with boron trifluoride were fulfilled to synthesize the tripod BODIPY dyes.As the controlled experiment of the nucleophilic substitution,two tris-substituted 1,3,5-triazine intermediates were also synthesized based on the reactions between the bis-substituted intermediate and amines(diethylamine and aniline).All the four new compounds had been characterized by 1H NMR,13 C NMR,HRMS and IR spectra.The photophysical properties of the fluorescent dyes were determined.The results showed that:1.The amine substitution reaction of the oxidized intermediate d could be carried out at a low temperature.2.For fluorescent compounds containing diethylamine and aniline,the maximum emission wavelength was of little difference.3.The fluorescent quantum yields of diethylamine dyes and aniline dyes were 54% and 41%,respectively.In order to further investigate the reaction mechanism of nucleophilic substitution at low temperature,the nucleophilic substitution reaction pathways of ammonia,diethylamine and aniline were calculated at the B3LYP/def2-TZVP level by density functional theory.The energy barrier of the reactions and charge transfer between the reaction complexes and the transition states were investigated,which proved that:1.All the reactions followed the two-step "addition-elimination" reaction mechanism.First,the amine nucleophiles attacked the substrate to form a ?-complex.And then a transition state formed,followed by the leaving of the HCl molecule to afford the final product.2.In the reaction process of the preparation of tripod BODIPY,the corresponding energy barrier of the replacement of the third Cl atom was lower,which was in great agreement with the experiment result that the raction could be carried out at a low temperature.3.The calculation results of the frontier orbital energy were the same as those result of energy barrier discussed above.