• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Resonance Raman and DFT Studies of Tetra-tert-butyl Porphine: Assignment of Strongly Enhanced Distortion Modes in a Ruffled Porphyrin
【24h】

Resonance Raman and DFT Studies of Tetra-tert-butyl Porphine: Assignment of Strongly Enhanced Distortion Modes in a Ruffled Porphyrin

机译：四叔丁基卟啉的共振拉曼和DFT研究：皱纹卟啉中强烈增强的失真模式的分配。

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

The free-base form of tetra-tert-butyl porphine (TtBP), which has extremely bulky meso substituents, is severely distorted from planarity, with a ruffling angle of 65.5°. The resonance Raman spectrum of TtBP (λ_(ex) = 457.9 nm) and its d_2, d_8, and d_(10) isotopomers have been recorded, and while the spectra show high-frequency bands similar to those observed for planar meso-substituted prophyrins, there are several additional intense bands in the low-frequency region. Density functional calculations at the B3-LYP/6-31G(d) level were carried out for all four isotopomers, and calculated frequencies were scaled using a single factor of 0.98. The single factor scaling approach was validated on free base prophine where the RMS error was found to be 14.9 cm~(-1). All the assigned bands in the high-frequency (>1000 cm~(-1)) region of TtBP were found to be due to vibrations similar in character to the in-plane skeletal modes of conventional planar prophyrins. In the low-frequency region, two of the bands, assigned as v_8 (ca. 330 cm~(-1)) and v_(16) (ca. 540 cm~(-1)), are also found in planar porphyrins such as tetra-phenyl porphine (TPP) and tetra-iso-propyl porphine (IPP). Of the remaining three very strong bands, the lowest frequency band was assigned as γ_(12) (pyr swivel, obsd 415 cm~(-1), calcd 407 cm~(-1) in d_0). The next band, observed at 589 cm~(-1) in the d_0 compound (calcd 583 cm~(-1)), was assigned as a mode whose composition is a mixture of modes that were previously labeled γ_(13) (γ(C_mC_aH_mC_a)) and γ_(11) (pyr fold_(asym)) in NiOEP. The final strong band, observed at 744 cm~(-1) (calcd 746 cm~(-1)), was assigned to a mode whose composition is again a mixture of γ_(11) and γ_(13), although here it is γ_(11) rather than γ_(13) which predominates. These bands have characters and positions similar to those of three of the four porphyrin ring-based, weak bands that have previously been observed for NiTPP. In addition there are several weaker bands in the TtBP spectra that are also "out-of-plane" vibrations. Two of these (878 and 902 cm~(-1)) correspond to the remaining 652 cm~(-1) NiTPP band, γ_(17) (γ(C_β - H)_(sym)), and are γ(C_β - H)_(sym) vibrations centered predominantly on the pyrrolidene or pyrrole rings. Since the intensities of resonance Raman bands can be used to map the changes in geometry associated with the electronic transitions lying at the excitation wavelength, the observation that the modes which are most strongly enhanced are those which involve distortion of the C_m - pyrrole - C_m segments away from their near-planar ground-state geometries may be significant. In particular, it points to distortions in the excited state along coordinates which are different to those found in the ground state. In the ground state, each of the C_m - pyrrole - C_m units in TtBP is near-planar, even in this very sterically challenged compound, but the overall structure is ruffled because these units are tilted with respect to each other. However, the enhanced modes do not follow this distortion coordinate but are associated with twisting within the C_m - pyrrole - C_m units and this suggests that these modes are important in the excited state.
机译：具有极大体积的内消旋取代基的四叔丁基卟啉（TtBP）的游离碱形式严重偏离平面度，其波纹角为65.5°。记录了TtBP（λ_（ex）= 457.9 nm）及其d_2，d_8和d_（10）同位素异构体的共振拉曼光谱，而该光谱显示的高频带类似于平面中观取代的卟啉所观察到的，在低频区域还有几个其他的强频带。对所有四个异构体进行了B3-LYP / 6-31G（d）水平的密度泛函计算，并使用0.98的一个因子来缩放计算的频率。单因素缩放方法已在游离碱丙酮中验证，RMS误差为14.9 cm〜（-1）。发现TtBP的高频（> 1000 cm〜（-1））区域中所有分配的频段归因于与常规平面卟啉的平面内骨架模式相似的振动。在低频区域，在平面卟啉中也发现了两个带，分别为v_8（约330 cm〜（-1））和v_（16）（约540 cm〜（-1））。作为四苯基卟啉（TPP）和四异丙基卟啉（IPP）。在其余三个非常强的频带中，最低的频带被指定为γ_（12）（pyr旋转，obsd 415 cm〜（-1），d_0计算为407 cm〜（-1））。在d_0化合物中在589 cm〜（-1）处观察到的下一个谱带（计算值为583 cm〜（-1））被指定为一种模式，其成分是先前标记为γ_（13）的模式的混合物NiOEP中的（C_mC_aH_mC_a）和γ_（11）（pyr fold_（asym））。在744 cm〜（-1）处观察到的最终强带（计算为746 cm〜（-1））被指定为一种模式，其成分再次为γ_（11）和γ_（13）的混合物。是γ_（11）而不是占主导地位的γ_（13）。这些条带的特征和位置与以前针对NiTPP观察到的四个基于卟啉环的弱条带中的三个相似。另外，TtBP谱中还有几个较弱的带，它们也是“平面外”振动。其中两个（878和902 cm〜（-1））对应于剩余的652 cm〜（-1）NiTPP带γ_（17）（γ（C_β-H）_（sym）），分别为γ（C_β -H）_（sym）振动主要集中在吡咯烷或吡咯环上。由于共振拉曼带的强度可用于绘制与激发波长处的电子跃迁相关的几何形状变化，因此观察到的最强烈增强的模式是涉及C_m-吡咯-C_m链段畸变的模式远离其接近平面的基态几何形状可能很重要。特别是，它指出了在激发态下沿坐标的变形，该变形与在基态下发现的不同。在基态下，即使在这种非常受空间挑战的化合物中，TtBP中的C_m-吡咯-C_m单元中的每一个均接近平面，但由于这些单元相对于彼此倾斜，所以整体结构起伏不定。但是，增强模式不遵循该变形坐标，而是与C_m-吡咯-C_m单位内的扭曲相关联，这表明这些模式在激发态下很重要。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号