Structures And Spectroscopic Properties Of Meso-tetrasubstituted Porphyrin And Metal Porphyrin Complexes Based On Density Functional Theory Calculations

Porphyrin and metalloporphyrin play more and more important roles and have wide applications in biomimietic chemistry,catalysis,utilization of solar energy,special type materials,medicine and analytical chemistry etc.To deepen the understanding of experimental results and provide theoretical guidance for further experimental research,many researchers decided to introduce quantum chemistry studies into their research.Molecular structures,atomic charges,molecular orbital energy gaps,electronic absorption spectra,and infrared(IR) spectra of twelve meso-tetrasubstituted porphyrin complexes including metal free porphyrins H₂Por(Por=TPP,TFPP,TClPP,TPyP)(1-4) and their metal complexes MPor(M=Mg,Zn;Por=TPP,TFPP,TClPP,TPyP)(5-12) [TPP=meso-tetrakis(phenyl)porphyrinate;TFPP=meso-tetrakis(4-fluorophenyl) porphyrinate;TClPP=meso-tetrakis(4-chlorophenyl) porphyrinate;TPyP= meso-tetrakis(4-pyridyl) porphyrinate]are systematically studied by density functional theory calculations at the B3LYP/6-31G(d) level with Gaussian03 program.Good consistency was found between the calculated molecular structures and experimental X-ray crystallography ones for 1,3,and 4,and between the simulated electronic absorption considering solvent effect and IR spectra and the experimental ones of 1 and 4.The calculation results reveal that introducing substituents at the meso positions of porphyrin induces increasing change in the molecular structures,atomic charges distribution,HOMO and LUMO energy,electronic absorption spectra,and IR spectra along with the increase in electron-withdrawing ability of substituents in the order phenyl,4-fluorophenyl,4-chlorophenyl,and pyridyl group.Furthermore,the central metal in porphyrins displays much significant influence on the structure and spectroscopic properties of meso-substituted porphyrin complexes.The electronic absorption and IR spectra of 1-12 are compared and assigned in detail.The present work should be not only helpful towards understanding the meso-substitutional and central metallic effects on the structure and spectroscopic properties of meso-substituted porphyrin complexes,but also useful in correctly assigning electronic absorption and IR spectra and further investigation of the vibration spectra of porphyrin analogues and metal complexes.