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):1110-24. doi: 10.1111/j.1751-1097.2007.00150.x.
Understanding the effects of substituents on the spectra of chlorins is essential for a wide variety of applications. Recent developments in synthetic methodology have made possible systematic studies of the properties of the chlorin macrocycle as a function of diverse types and patterns of substituents. In this paper, the spectral, vibrational and excited-state decay characteristics are examined for a set of synthetic chlorins. The chlorins bear substituents at the 5,10,15 (meso) positions or the 3,13 (beta) positions (plus 10-mesityl in a series of compounds) and include 24 zinc chlorins, 18 free base (Fb) analogs and one Fb or zinc oxophorbine. The oxophorbine contains the keto-bearing isocyclic ring present in the natural photosynthetic pigments (e.g. chlorophyll a). The substituents cause no significant perturbation to the structure of the chlorin macrocycle, as evidenced by the vibrational properties investigated using resonance Raman spectroscopy. In contrast, the fluorescence properties are significantly altered due to the electronic effects of substituents. For example, the fluorescence wavelength maximum, quantum yield and lifetime for a zinc chlorin bearing 3,13-diacetyl and 10-mesityl groups (662 nm, 0.28, 6.0 ns) differ substantially from those of the parent unsubstituted chlorin (602 nm, 0.062, 1.7 ns). Each of these properties of the lowest singlet excited state can be progressively stepped between these two extremes by incorporating different substituents. These perturbations are associated with significant changes in the rate constants of the decay pathways of the lowest excited singlet state. In this regard, the zinc chlorins with the red-most fluorescence also have the greatest radiative decay rate constant and are expected to have the fastest nonradiative internal conversion to the ground state. Nonetheless, these complexes have the longest singlet excited-state lifetime. The Fb chlorins bearing the same substituents exhibit similar fluorescence properties. Such combinations of factors render the chlorins suitable for a range of applications that require tunable coverage of the solar spectrum, long-lived excited states and red-region fluorescence.
了解取代基对二氢卟吩光谱的影响对于众多应用而言至关重要。合成方法学的最新进展使得对二氢卟吩大环性质随取代基类型和模式变化的系统研究成为可能。在本文中，对一组合成二氢卟吩的光谱、振动和激发态衰变特性进行了研究。这些二氢卟吩在5、10、15（中位）位置或3、13（β）位置带有取代基（一系列化合物中还有10 - 均三甲苯基），包括24种锌二氢卟吩、18种游离碱（Fb）类似物以及一种Fb或锌氧化卟吩。氧化卟吩含有天然光合色素（如叶绿素a）中存在的含酮异环。通过共振拉曼光谱研究的振动性质表明，取代基对二氢卟吩大环结构没有显著扰动。相比之下，由于取代基的电子效应，荧光性质发生了显著改变。例如，带有3,13 - 二乙酰基和10 - 均三甲苯基的锌二氢卟吩的最大荧光波长、量子产率和寿命（662 nm，0.28，6.0 ns）与未取代的母体二氢卟吩（602 nm，0.062，1.7 ns）有很大差异。通过引入不同的取代基，可以在这两个极端之间逐步调节最低单重激发态的每一个性质。这些扰动与最低激发单重态衰变途径的速率常数的显著变化相关。在这方面，具有最红荧光的锌二氢卟吩也具有最大的辐射衰变速率常数，并且预计具有最快的非辐射内转换至基态。尽管如此，这些配合物具有最长的单重激发态寿命。带有相同取代基的Fb二氢卟吩表现出相似的荧光性质。这些因素的组合使得二氢卟吩适用于一系列需要可调谐覆盖太阳光谱、长寿命激发态和红光区域荧光的应用。
