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首页> 外文期刊>RSC Advances >The influence of protonation on the structure and spectral properties of porphine: UV-vis, 1H NMR and ab initio studies
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The influence of protonation on the structure and spectral properties of porphine: UV-vis, 1H NMR and ab initio studies

机译：质子化对卟啉结构和光谱特性的影响：UV-Vis，1H NMR和AB Initio研究

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In this study, protonation of porphine (H _(2) P) with a range of weak and strong acids was investigated. The dication of H _(2) P was water soluble and therefore UV-vis and ~(1) H NMR studies were performed in water and D _(2) O as well as in dichloromethane and dimethylformamide. In contrast to the dication of other porphyrins, protonated species of H _(2) P were completely decomposed upon evaporation of solvent at room temperature and therefore were studied in solution. Also, high level ab initio calculations were used to predict the structure, frontier molecular orbitals and transition energies of H _(2) P dication. The Soret band of H _(2) P was only slightly shifted to longer or shorter wavelengths in reaction with weak and strong acids, respectively. The results show that the presence of aryl or at least alkyl substituents at the meso positions of porphyrin macrocycle is necessary for the observation of significant red shifts of the Soret band. In the case of the Q(0,0) band, large blue shifts of the band were observed for the dications that correlate with the absence of any π electron-donating group at the meso position. In ~(1) H NMR spectra, signals for both the β and meso protons were shifted downfield, which shows the negligible decrease in the porphine ring current caused by the out-of-plane distortion of the macrocycle. While ab initio calculations show a saddle shaped conformation for [H _(4) P] ~(2+) , H _(4) P(CF _(3) COO) _(2) was found to adopt an unusual wave conformation that clearly differs from that of previously characterized dications of meso -tetra(aryl)- and meso -tetra(alkyl)porphyrins. Also, the calculations on monoprotonated species show that [H _(3) P] ~(+) and H _(3) P(CF _(3) COO) adopt a nearly saddle type and dome shaped conformation, respectively. On the other hand, the energies of absorption bands of H _(4) P(CF _(3) COO) _(2) calculated at the TD-B3LYP/cc-pVDZ level of theory predicted the red shift of the Soret band and the blue shift of the Q(0,0) bands that are in accord with the results of UV-vis studies. The results revealed the role played by the acid molecules on the blue shift of the Q(0,0) band of the diprotonated species. Furthermore, the calculated changes in the bond lengths and bond angles show that the involvement of in-plane nuclear reorganization (IPNR) in the observed red shifts of the Soret and Q(0,0) bands cannot be excluded.
机译：在该研究中，研究了具有一系列弱和强酸的卟啉（H _（2）P）的质子化。 H _（2）P的溶剂是水溶性，因此在水和D _（2）O以及二氯甲烷和二甲基甲酰胺中进行UV-Vis和〜（1）H NMR研究。相反，与其他卟啉的脱离可选，在室温下蒸发溶剂时完全分解H _（2）P的质子化物质，因此在溶液中进行了研究。此外，使用高级别AB初始计算来预测H _（2）P Dation的结构，前沿分子轨道和转变能量。 H _（2）P的脱光带分别仅略微移至与弱和强酸反应的更长或更短的波长。结果表明，在卟啉宏循环的中间位置处存在芳基或至少烷基取代基对于观察Soret带的显着红色偏移是必要的。在Q（0,0）带的情况下，对于在MESO位置处于不存在任何π电子给予的基团的情况下，观察到带的大的蓝色偏移。在〜（1）H NMR光谱中，β和中间质子的信号被移位下场，其表示由宏循环的面外变形引起的卟啉环电流的可忽略不计。虽然AB初始计算显示[H _（4）P]〜（2+），H _（4）P（CF _（3）COO）_（2）被发现采用异常波构象的鞍形构象清楚地与先前表征的甲磺酸和甲基β-烷基（烷基）卟啉的特征症的染额不同。此外，单议议性的计算表明，[H _（3）p]〜（+）和H _（3）P分别采用近鞍型和圆顶形构象。另一方面，在TD-B3LYP / CC-PVDZ水平的TD-B3LYP / CC-PVDZ水平下计算的H _（4）P（CF _（3）COO）_（2）的吸收带的能量预测了SORET带的红色偏移而Q（0,0）频段的蓝色偏移，符合UV-VIS研究的结果。结果表明，酸分子在曲调物种Q（0,0）带的蓝色偏移上的作用。此外，键合长度和键角的计算变化表明，不能排除在观察到的索引和Q（0,0）带的观察到的红色移位中的面内核重组（IPNR）的参与。

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