Kee Hooi Ling, Kirmaier Christine, Tang Qun, Diers James R, Muthiah Chinnasamy, Taniguchi Masahiko, Laha Joydev K, Ptaszek Marcin, Lindsey Jonathan S, Bocian David F, Holten Dewey
Department of Chemistry, Washington University, St. Louis, MO, USA.
Photochem Photobiol. 2007 Sep-Oct;83(5):1125-43. doi: 10.1111/j.1751-1097.2007.00151.x.
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 Qy 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 Qy 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 (By, Bx, Qx, Qy) 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 photophysical properties of the chlorins. These insights form a framework that underpins the rational design of chlorins for applications encompassing photomedicine and solar-energy conversion.
本文给出了24种合成锌二氢卟吩和18种游离碱类似物的光吸收光谱及氧化还原性质，这些化合物带有多种3,13（β）和5,10,15（中位）取代基。还给出了锌氧代卟吩和游离碱氧代卟吩的相关结果，它们含有天然光合色素如叶绿素a中存在的含酮异环。进行了密度泛函理论计算，以探究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。一个普遍的发现是，3,13位比5,10,15位对助色团的影响更敏感。所研究的助色团（乙酰基>乙炔基>乙烯基>芳基）在3,13位时会导致Qy带显著红移和增强，而在5,10,15位的基团导致的红移要小得多，同时伴随相对Qy强度的降低。此外，取代基引起的第一氧化和还原电位的变化分别忠实地跟踪了最高占据分子轨道和最低未占据分子轨道（HOMO和LUMO）的能量。计算表明，取代基对LUMO的影响比对HOMO的影响更大，这源于两个轨道在取代基位点处电子密度的差异。利用Gouterman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（By、Bx、Qx、Qy）的波长和相对强度的影响趋势，该模型除了考虑取代基对HOMO和LUMO的影响外，还考虑了对HOMO - 1和LUMO + 1的影响。总体而言，本文及配套论文中给出的结果和分析为取代基对二氢卟吩的光吸收、氧化还原及其他光物理性质的影响提供了见解。这些见解构成了一个框架，为包括光医学和太阳能转换在内的二氢卟吩应用的合理设计奠定了基础。
