Theoretical Study On The Inner Hydrogen Atom Transfer And Absorption Spectra Of Metal Substitution Effect In Free Porphyrin And N/Neo-confused Porphyrin

Porphyrins and metal porphyrins play an important role in medicine, catalysis,spectroscopy materials, dye sensitized solar cells and so on. Quantum chemical calculationsplay an important role to study the porphyrin compounds in the above several areas. Thepaper uses Gaussian03package to study the hydrogen migration process in NECP andsubstituents impact on it, as well as absorption spectra of free porphyrins and n/neo-confusedporphyrin porphyrin coordination with metal were studied and analyzed.The process of two hydrogen atoms migrating in four N atoms of porphyrin compoundsis called tautomerism of NH, the role of this reaction is important to light synthesis and metalcoordination chemistry. Based on density functional theory (DFT) calculations were carriedout to study the infuence of both fuorine (meso-position) and cycloheptane (on invertedpyrrole ring) substituents on the inner hydrogen migration in Neo-Confused Porphyrin. Stablestructures and transition states are fully optimized at the B3LYP/6-31G (d, p) level. It is foundthat the acidity of the migration hydrogen atom, the basicity of the nitrogen atoms of theadjacent pyrrole rings, the distance from the migrated hydrogen atom to the nitrogen atom ofthe adjacent pyrrole rings and the electronic nature of substituents (fuorine and cycloheptane)have signifcant infuences on the potential energy barrier of the inner hydrogen migration inporphyrins.On the basis of detailed density functional theory, the molecular geometrical structures andorbital energy levels of free base porphyrin (FBP), neo-confused porphyrin (NECP) andn-confused porphyrin(NCP) coordinated with Mg, Ni, Cu, Zn were studied atB3LYP/6-31+G(d) level. The electronic absorption spectrum of metal coordinated with threekinds of porphyrins are studied in gas phase at time dependent density functional level,including the excitation energy, absorption wavelength, oscillator strength and the orbitalcomposition of the electronic transition, and three different solvents (water, chloroform andbenzene) state influencing on the electronic absorption spectrum is also researched. Accordingto the result, Since the metal coordinated with FBP (M-FBP) having D4hsymmetry,HOMO/HOMO-1, LUMO/LUMO+1have similar orbital energy level occurs degeneracy, theenergy gap of HOMO-LUMO is about3.0eV, Soret band has a strong absorption peak. For theasymmetric structure NECP coordinated with metal (M-NECP). Due to change of C/N atomin center structure of NECP, M-NECP molecular frontier orbitals composition compared withM-FBP have changed. Molecular orbital energy gap (HOMO-LUMO) is reduced to about2.6eV, M-NCP is about2.3eV. Both of them energy level are splits, Soret band appears more strong electronic absorption peaks, Q absorption band also appeared. Under the conditions ofsolvent state the electronic absorption spectra of M-FBP, M-NECP and M-NCP red shift alongwith the weaken polarity of solvent (water, chloroform, benzene) and enhanced absorptionpeak intensity.