密度泛函理论研究5-单苯基卟啉分子的几何结构和拉曼光谱

利用密度泛函理论(DFT)计算了5-单苯基卟啉(H2MPP)的几何结构和拉曼振动频率. 计算表明, 单个次甲基位置上的苯基取代降低了卟啉骨架大环的对称性. 苯基团取代对次甲基位置附近结构的影响较大, 而对吡咯环结构的影响较小. 计算给出的拉曼振动频率(校正因子为0.971)与实验测量数据吻合较好, 均方根误差(RMS)小于6.7 cm-1. 根据理论计算结果对实测拉曼光谱进行了指认, 计算分析和实验观察同时表明, 单个次甲基位置上的苯基取代导致卟啉大环的一些平面内简正振动, 如ν6、ν20、ν24和ν32等简正振动发生分裂. 分析认为其根本原因为单苯基取代导致的卟啉骨架大环对称性的降低.

DFT Study on the Geometric Structure and Raman Spectrum of meso-monophenylporphyrin (H2MPP)

The geometric structure and Raman frequencies of meso-monophenylporphyrin (H2MPP) were studied by density-functional-theory (DFT). The calculation indicates that meso-monophenyl substitution induces larger distortion to meso-position than to pyrrole ring. All calculated frequencies were scaled with a single factor of 0.971, which gives acceptable results compared with experimental data (the RMS is 6.7 cm-1). The measured Raman spectra were discussed and the assignment of in-plane vibrational normal mode of porphyrin ring was given on the basis of theoretical calculation. Further analysis indicates the splits of some in-plane vibrational normal modes of porphyrin ring (for instance ν6, ν20, ν24, and ν32 mode), which was attributed to the diversification of the structure around Cm atoms and pyrrole structure induced by meso-monophenyl substitution.