Theoretical Investigations Of The Electronic Absorption Spectra Of Neo-Confused Porphyrins And Heteroatom-Containing Prophyrins

A majority of solar energy cannot be absorbed by porphyrin materials,including the rare light absorption region from 500 nm to 600 nm and the weak intensity absorption region from 600 nm to 700 nm.If the materials are modified based on the porphyrin structure,the new derivatives with more absorption peaks and higher absorption intensities will expand the potential application in various fields,such as nonlinear optics materials,photodynamic therapy and photosensitive solar cells.The mainstream modifications of porphyrin are the replacement of the substituents in the side of the scaffold and the metal-coordination in the cavity of the porphyrin center.However,the above modifications has little effect on the irmprovement of porphyrin properties.As a primary consideration and upstream for modifying the core structure of porphyrin,the N position alteration strategy and heteroatomic substitution would be more accessible to find the new porphyrin materials with broader absorption wavelength range and higher intensity.It is significant that a series of new porphyrin materials with side substituents can be effortlessly developed on the basis of the modified core structures.So applied with density function theory(DFT)and time dependent density function theory(TDDFT),the systematic researches on the various properties of neo-confused porphyrins,heteroatom-containing porphyrins and metal-coordinated heteroatom-containing porphyrins were conducted in this thesis.The main research results are as follows:(1)The N-C exchange strategy significantly brought about the asymmetrical charge distribution and structure of the new porphyrins.The dipole moment of benzoporphyrins BN-CP(1.4015 Debye)was 2.6 times higher than tihat of BenP(0.5326 Debye),v^iile the energy gap of HOMO-LUMO decreased by 0.5eV.BN-CP could absorb long wavelength light and vary its properties to absorb shorter wavelength visible light in different polarity solvents.The novel porphyrin derivative NiBN-CP broadened absorption bands and three absorption peaks located at 514 nm,577 nm and 623 nm.The repulsion of four inner hydrogen atoms deform the protoned benzoporphyrin to a saddle shape molecule and destroy the conjugation structure,resulting in the decrease of the total molecule energy,the significant splitting in the Soret bands and multi-band absorption property.The C-N exchange strategy can vary the molecular symmetry and molecular orbital composition,more orbitals(L+2,H-3,H-4 and so on)participated the electronic transition and some forbidden transitions turned to weak allowed transitions to raise the photon absorption probability.(2)The C-N swap strategy remarkably varified the porphyrin and led to a low symmetry structure and the reduction of orbital degeneration,which enriched the energy transition patterns and pathways.Compared the absorption spectra of BenP,die maximum absorption peak in Q band of N-CP red shifted 70 nm.Ni and Zn further influence the frontier molecular orbital and absorption spectrum.With the 3d10 electron distribution,the divalent cation Zn2+can stabilize the neo-confused porphyrin,provide electrons for the whole conjugated molecule,and improve the visible light absorption property.All these properties make Zn-N-CP extremely attractive candidates for use in dye,photo sensitization,solar energy conversion and photo dynamic therapy fields.(3)As the replacement of pyrrole,the phosphene altered the core conjugation structure of porphyrin.In monophosphole-containing and diphosphole-containing porphyrins,the phosphorus atom deviated from the porphyrin plane and resulted in non-planar configuration derivatives.The dipole moments of protonated phosphole-containing porphyrins,PN3H-Porphyrin(PN3H-P)and P2N2H-Porphyrin(P2N2H-P),were significantly affected by the polarities of solvents.The HOMO-LUMO energy gap of phosphorus-containing porphyrins obviously reduced compared with free based porphyrin(FBP)because the s and p orbitals composed the LUMO,HOMO,H-1,H-2 and other orbitals of the phosphorus-containing derivatives.With the effects of phosphorus orbitals and electrons on the frontier orbitals energy levels of new molecules,the light absorption range and intensity of phosphorus-containing porphyrins significantly increased than the properties of FBP.Besides,the light absorption range and intensity of these derivatives were dramatically red-shifted along with the decrease of the polarities of solvents.(4)The charge distribution and structures of dioxaporphyrin,dithiaporphyrin and oxathiaporphyrin of which N or NH were displaced by O or S were significantly different from those of FBP.Though the three heteroatom containing derivatives maintained the planar configuration,the symmetry of reduced and the distances of inner N-N increased obviously.As the replacement of nitrogen atoms in N202-P,the oxygen atoms contributed to a better electron transition.The Q band absorption peaks located at 594 nm and 522 nm displayed the better optical performance than that of FBP in visible region.With the same symmetry and similar electron distributions,the similar calculated absorption spectrum of dioxaporphyrin and dithiaporphyrin demonstrated that both materials possess similar physical-chemical properties.However,the higher values of oscillator strength were observed in dithiaporphyrin,which can be ascribed to the participation of p orbitals from sulfur atoms.The symmetry of oxathiaporphyrin further reduced to C2v,symmetric structure,which lead to the lower degeneration of molecular energy levels and more complicated theoretical absorption spectrum.The Q band absorption peaks located at 597 nm and 533 nm showed higher absorption intensity and higher oscillator strengths of oxathiaporphyrin than that of dithiaporphyrin.(5)After the sectondary modification with zinc coordination,the molecular configuration and properties emerging new changes in the heteroatom-containing porphyrins.In FBP-Zn the large energy gap between HOMO and LUMO was observed according to the calculation results.It is heartening that the energy gap of HOMO-LUMO narrowed significantly and the degeneracy of energy level declined greatly in Zinc coordinated heteroatom-containing porphyrins.The transition metal Zinc and the heteroatoms brought about enormous changes in the frontier orbitals compositions and the energy levels.Consequently,more electron transfer pathways and forms would cause a growing number of absorption peaks and the enlargement of absorption range in visible light region.Zn coordinated oxathiaporphyrin possessed both optical characteristic of Zn coordinated dioxaporphyrin and dithiaporphyrin.The peak located at 484 nm blue shifted with the increase of solvent polarity,while the Soret band and Q band peaks shifted diversely in different solvents.The variations of the spectrum,including the broadening absorption range and the increase the number of peaks,illustrated that the zinc atom and heteroatoms evidently changed the optical characters of porphyrins.