Theoritical Studies on the Structure and Absorption Spectra of Neo-Confused Metal Porphyrin†

Abstract

On the basis of detailed density functional theory( DFT),the molecular geometrical structures and orbital energy levels of free base porphyrin( FBP) and neo-confused porphyrin( NECP) coordinated with Mg, Ni,Cu,Zn were studied at B3LYP /6-31 + G( d) level. The electronic absorption spectra of metal coordinated porphyrins were studied in gas phase at time dependent density functional level,including the excitation energy,absorption wavelength,oscillator strength and the orbital composition of the electronic transition. Since the metal coordinated FBPs( M-FBP) have D 4h symmetry,HOMO / HOMO- 1,LUMO / LUMO + 1 degenerate respectively with the similar orbital energy level. The energy gaps of HOMO-LUMO of M-FBPs are about 3. 0 eV. The structure and orbital properties of M-FBPs evolve strong Soret bands in the absorption spectra. Due to the change of C / N atom in the center structure of NECP,M-NECP molecular frontier orbitals composition is more complicated than that of M-FBP. In M-NECPs,the molecular orbital energy gaps( HOMO-LUMO) reduce to about 2. 6 eV. The C / N exchange strategy can vary the molecular symmetry and molecular orbital composition of M-NECPs,which leads to the energy level splitting,strong electronic absorption peaks of Soret band and the appearance of Q absorption band. All the parameters of M-FBPs and M-NECPs were investigated in three different solvents( water,chloroform and benzene). Under the solvent conditions,the electronic absorption spectra of M-FBP and M-NECP take place red shift along with the weaken polarity of solvent( water, chloroform,benzene) and enhance the absorption peak intensity.