Study On Circular Dichroism Specturm Of Porphyrins Macrocylic Compound

Circular dichroism(CD) spectrum, as spectrum probe for the research of molecularchirality, has wonderful application prospect in studying biochemistry, molecular absoluteconfigurations and protein dynamics. The most important subject in this field is the researchof exploring the origin of CD, establishing the relation between structures and spectruminformations, which has theoretical significance and application value.We chose para-/meta-/ortho-(S)-binaphthyl bridged bis-porphyrin(S-BINOL(Por)2)molecules1,2,3as model compound, adopted three theoretical models of DeVoe method ofclassic electromagnetism polarizability theoty for the CD calculating of1,2,3. Molecularconfigurations were optimized on DFT/B3LYP/3-21G*level to obtain structural parameters.In order to obtain spectroscopic parameters, we fit the experimental UV spectrum ofcorresponding monomers by Lorentzian linear function. We found that, different models fitfor the molecules with different substituent sites. To para-site molecule1, the CD curces witheffective transition moment model had the best agreement with experimental spectrum, tometa-site2, the best fitting curve was the result of hybrid model. To ortho-site3, effectivetransition moment model got the best curve with the band shape has errors. It was illustratedthat the π-π stacking appeared in molecule3may not conform to the isolated systemapproximation adpoted by DeVoe method. The amplitude sequence predicted by DeVoemethod was corresponded with the amplitude sequence of experimental spectrum, conformedto the prediction of exciton coupling theory, which means, the CD arise from the excitoncoupling between the two porphyrin rings. DeVoe method could be used to predict CD ofbis-porphyrins with good agreement.We extend the DeVoe method to corrole, a kind of porphyrinoid compound, for the firsttime. We chose para-/meta-(S)-binaphthyl bridged bis-corrole(S-BINOL(Cor)2) molecules4,5for CD calculating, explore the influence of corrole’s asymmetry on introduced circulardichroism(ICD) spectrum. Corrole has asymmetry for the reason of a carbon atom missed incorrole ring. The B band of UV spectrum is significant split, which arise from the two kindsof tautomers of corrole a,b, due to the inner NH protons migrate around the ring. This wasproved by theoretical calculations. We chose double-peak Lorentzian linear function fittingmethod to fit the UV spectrum, obtained a long-wavelength oscillator and a short-wavelengthoscillator and relevant spectroscopic parameters.We calculated CD curves for aa, bb, abtautomers of4,5. The result shows that when considere all these three kinds of tautomers, the calculated curve has the best agreement with experimental spectrum, we give both long andshort-wavelength oscillator parameters to ab tautomer. It is illustrated that the origin of CD ofbis-corroles is still the exciton coupling between the chromophores, and DeVoe method isfeasible for the CD calculating of bis-corrole system.