Effects of substituents on synthetic analogs of chlorophylls. Part 2: Redox properties, optical spectra and electronic structure
Effects of substituents on synthetic analogs of chlorophylls. Part 2: Redox properties, optical spectra and electronic structure
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DOI：
10.1111/j.1751-1097.2007.00151.x
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发表时间：
2007-09-01
影响因子：
3.3
通讯作者：
Hoten, Dewey
中科院分区：
文献类型：
--
作者：
Kee, Hooi Ling;Kirmaier, Christine;Hoten, Dewey
显示了 24 种合成二氢锌二氢卟酚和 18 种带有各种 3,13（β）和 5,10,15（内消旋）取代基的游离碱类似物的光学吸收光谱和氧化还原性质。还给出了锌和游离碱氧代佛宾的结果，它们含有天然光合色素（如叶绿素 a）中存在的带酮基等环。通过密度泛函理论计算，探讨取代基的类型和位置对前沿分子轨道特征（能量、电子分布）的影响。普遍的发现是，3,13 位对助色团的影响比 5,10,15 位更敏感。助色体；研究的基团（乙酰基>乙炔基>乙烯基>芳基）在放置在3,13位置时引起Q（y）带的显着红移和增强，而位于5,10,15位置的基团导致更小的红移，并伴随着相对Q（y）强度的降低。此外，取代基引起的第一氧化和还原电势的变化分别忠实地追踪最高占据和最低未占据分子轨道（HOMO和LUMO）的能量。计算表明，LUMO 比 HOMO 因取代基而发生的位移更多，这是由于取代基位点上两个轨道的电子密度差异所致。使用 Gouterman 的四轨道模型可以很好地解释取代基对近紫外到近红外吸收带中主要特征（B-y、B-x、Q(x)、Q(y)）的波长和相对强度的影响的趋势，该模型除了 HOMO 和 LUMO 之外还结合了取代基对 HOMO-1 和 LUMO+1 的影响。总的来说，本文和配套论文中提出的结果和分析提供了取代基对二氢卟酚的光学吸收、氧化还原和其他光物理性质的影响的见解。这些见解形成了一个框架，支撑二氢卟酚在光医学和太阳能转换等应用中的合理设计。
The optical absorption spectra and redox properties are presented for 24 synthetic zinc chlorins and 18 free base analogs bearing a variety of 3,13 (beta) and 5,10,15 (meso) substituents. Results are also given for a zinc and free base oxophorbine, which contain the keto-bearing isocyclic ring present in the natural photosynthetic pigments such as chlorophyll a. Density functional theory calculations were carried out to probe the effects of the types and positions of substituents on the characteristics (energies, electron distributions) of the frontier molecular orbitals. A general finding is that the 3,13 positions are more sensitive to the effects of auxochromes than the 5,10,15 positions. The auxochromes; investigated (acetyl > ethynyl > vinyl > aryl) cause a significant redshift and intensification of the Q(y) band upon placement at the 3,13 positions, whereas groups at the 5,10,15 positions result in much smaller redshifts that are accompanied by a decrease in relative Q(y) intensity. In addition, the substituent-induced shifts in first oxidation and reduction potentials faithfully track the energies of the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO), respectively. The calculations show that the LUMO is shifted more by substituents than the HOMO, which derives from the differences in the electron densities of the two orbitals at the substituent sites. The trends in the substituent-induced effects on the wavelengths and relative intensities of the major features (B-y, B-x, Q(x), Q(y)) in the near-UV to near-IR absorption bands are well accounted for using Gouterman's four-orbital model, which incorporates the effects of the substituents on the HOMO-1 and LUMO+1 in addition to the HOMO and LUMO. Collectively, the results and analysis presented herein and in the companion paper provide insights into the effects of substituents on the optical absorption, redox and other photo-physical properties of the chlorins. These insights form a framework that underpins the rational design of chlorins for applications encompassing photomedicine and solar-energy conversion.