不同电子取代基卟啉化合物的光谱和DFT研究

Porphyrins with Different Electron Groups:Spectral and DFT Study

采用实验与密度泛函理论计算(DFT)相结合,研究了不同电子取代基修饰的5-邻羟基苯基-10,15,20-三苯基卟啉(TPPOH)和5-邻羟基苯基-10,15,20-三(对甲氧基)苯基卟啉[(p-OCH_3)TPPOH]化合物的吸收光谱及其电化学性质。结果表明,相对于TPPOH,由于对位甲氧基(-OCH_3)给电子能力强致使(pOCH_3)TPPOH的卟啉环电子云密度增加,从而引起吸收光谱红移(3 nm)、氧化还原电位发生明显的负移,最高占据分子轨道(HOMO)和最低空轨道(LUMO)能级差降低0.06 eV。DFT理论分析分子前线轨道电子分布结果显示(p-OCH_3)TPPOH的HOMO和LUMO轨道能量均增加,而能级差却比TPPOH能级差小0.05 eV。理论结果与电化学和光谱实验结论一致,并进一步阐明了光谱和电化学性质变化机理,为揭示不同取代基卟啉化合物的设计与应用提供重要依据。

UV-Vis absorption spectra and electrochemical properties of 5-（o-hydroxyphenyl）-10 ,15 ,20-tri-（p-phenyl）porphyrin （TPPOH） and 5-（o-hydroxyphenyl）-10 ,15 ,20-tri-（p-methoxyphenyl）porphyrin [（p-OCH3 ）TPPOH] with different electron groups were investigated by experiments and density functional theory （DFT ） .Due to the introduction of para-methoxyl group （-OCH3 ） ,obvious red shift of 3 nm in the maximum absorbance of the UV-Vis spectra ,negative shift in redox potential of （p-OCH3 ）TPPOH ,and the decrease （0 .06 eV） in the energy gap （DE） of the frontier highest occupied molecular orbital （HO-MO） and the lowest unoccupied molecular orbital （LUMO） （of （p-OCH3 ）TPPOH occurred as compared to those of TPPOH . The results are due to that electron donating groups of -OCH3 increase the electron density of porphyrin ring in （p-OCH3 ）TP-POH .Electron distributions of the frontier orbital calculated by DFT showed that the increase in the energy levels of HOMO and LUMO ,while the decrease of 0 .05 eV in the energy gap .The agreement between experimental result and theoretical value and the further illustration of the mechanism for the spectral change and electrochemical properties provide important bases for the design and application of the porphyrin derivatives with different electron groups .