Theoretical Study On Electronic Spectrum Properties Of Hexaphyrins And Related Complexes

Even though the first expanded porphyrin, a22π macrocycle named “sapphyrin”, wasserendipitously discovered by Woodward and co-workers in1966, significant advancement inexpanded porphyrin chemistry was made only after the several decade because of thenonavailability of efficient methodologies to synthesize them in decent yields. However,contributions, particularly from the Sessler at university of Texas, Osuka at Kyoto Universityand Chandrashekar at Indian Institute of Technology groups, have played a key role indeveloping this area of chemistry. Due to the increased number π electron and varying cavitysizes compared with porphyrin, expanded porphyrins have attracted considerable attentiondue to their rich chemical properties such as in near-infrared dyes, anion sensors, two-photonabsorption, nonlinear optical materials, photodynamic therapy, multiple conformationalchanges, aromatic and anti-aromatic changes. Studies of hexaphyrins are the most widely inmangy expanded porhpyrin. In the present thesis, the DFT methods have been carried out toinvestigate molecular structures, protonated, aromaticity, the second-order nonlinear opticalproperties and absorption spectrum. The present work has focus on the following four aspects:1. The electronic properties, absorption spectrum and NICS(0) of hexaphyrin fromhexaphyrin(1.0.0.1.0.0) to hexaphyrin(1.1.1.1.1.1) were investigated by the TD-DFT methods.ΔEH-Lof aromatic molecules has much less changed comparison of free and protonatedcompounds. But for the antiaromatic molecules, ΔEH-Ldistinctly increases, when freecompounds became protonated compounds. Molecule3b has aromatic molecular that isapproved by the calculated NICS value, absorption spectrum and HOMA. As can be seenfrom atomic charge populations, molecules1a-4a are easy to protonated reaction comparingwith5a and6a. For the antiaromatic molecules of24π electron, The main contributions of theQ-like bands are the H�'L+1transition, those of B-like band are degenerate orbitalsH-1(H-2，H-3，H-4)�'L transition characterized by broad and ill-defined absorption spectra.In contrast, for the B-like band of aromatic molecules of26π electron, the absorption spectraexhibit a strong peak from H�'L and H-1�'L+1, the main contributions of the Q-like bandsare the H�'L+1transition2. Conformations, absorption spectrum, NLO, electronic states of26π and28π ofhexaphyrin(1.1.1.1.1.1) were investigated. A comparison of the molecular energies ofmolecules revealed that energy of T shape is the highest, not only26π molecules but also28πmolecules. M28that is same with other26π aromatic molecules has a similar electronicstructure. And M26that is same with other28π antiaromatic molecules has a similarelectronic structure. The maximal absorption of Hückel aromatic expanded porphyrins isinverse proportion with the ΔEH-L. The maximal absorption of Hückel antiaromatic expanded porphyrins is direct proportion with the ΔEH-L. Whether the Q-band or B-band, absorptionpeaks of aromatic molecules have a remarkable red shift comparing with the antiaromaticmolecules. The main contributions of the Q-like bands of aromatic molecules come from theH�'L and H-1�'L+1transition. But these of antiaromatic molecules come from H-1�'L andH�'L+1. For the transition of B-band, contributions of aromatic molecules come fromH-1�'Land H-1�'L+1. But spectrum of antiaromatic molecules shows broad B-like bandsform H-2�'L and H�'L+2. In addition, second-order nonlinear optical coefficient ofcontorted expanded porphyrins is bigger than planted complanate ones. And the second-ordernonlinear optical coefficient of anti-aromatic molecules is greater than the aromatic molecules3. The electronic properties of Pd(II) complexes of [26]Hexaphyrin (1.1.1.1.1.1) wereinvestigated using TD-DFT methods. For the three aromatic monometallic complexes, themaximal absorption shows λmaxD26Pd1>λmaxR26Pd1>λmaxM28Pd1that is inverse proportion with theΔEH-L. Compared with the corresponding ligands, maximal absorptions of D26Pd and M28Pdhave a blue shift, but R26Pd bring forth the red shift. For the D26Pd and M28Pd, the maincontribution of the Q-like bands is the π�'π*transition, which comes from ILCT. For theR26Pd, d orbital of the Pd(II) partly participated in the transition of Q-like bands, whichcomes from ILCT and MLCT. Compared with the free ligands, absorption of complexes thatis d(metal)�'π*coming from MLCT shows about20nm blue shift in the B-like band. Inaddition, second-order nonlinear optical coefficient of complexes shows β0(M28Pd1)>β0(D26Pd1)>β0(R26Pd1), and is bigger than one of ligands. So coordinated metal help toincrease second-order nonlinear optical coefficient, due to dipole moment change comingfrom transition of d(metal)�'π*is probably bigger than that of π�'π*.4. The electronic properties of group12bis-metal complexes of [26]Hexaphyrin(1.1.1.1.1.1) were investigated using the LDM and TD-DFT methods. By analyzing thechanges in energy and frontier molecular orbitals, bis-Hg-hexaphyrin was found to formR-shaped complex easily, whereas bis-Cd-hexaphyrin and bis-Zn-hexaphyrin form D-shapedcomplexes. Their transition natures are also similar because of their similar structures. Themain contribution of the Q-like bands is the π�'π*transition, which comes from ILMC. Incontrast, for the B-like band, the absorption spectra exhibit LMCT characteristics due to thecontributions from the metal atoms of HOMOs. Interestingly, for the B-like band of theD-shape complexes, the absorption is attributed to HOMO-1to LUMO, which results fromthe π-conjugation of HP-metal-phenyl (a)-metal-phenyl (b)-HP. The results prove that theLDM theory can explain the mutual effects of the atomic orbitals.