Mirror symmetry and vibrational structure in optical spectra of chlorophyll a
Mirror symmetry and vibrational structure in optical spectra of chlorophyll a
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DOI：
10.1063/1.3125183
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发表时间：
2009-05-21
影响因子：
4.4
通讯作者：
Freiberg, Arvi
中科院分区：
文献类型：
--
作者：
Raetsep, Margus;Linnanto, Juha;Freiberg, Arvi
采用常规和选择性光谱方法研究了叶绿素a在不同有机溶剂（中心Mg原子为五配位或六配位）下的吸收和荧光发射光谱。由于frank - condon和Hertzberg-Teller相互作用，与最低能量Q(y)跃迁有关的基本模型镜像对称规则被破坏。利用烧空穴荧光线窄化技术揭示了基电子态中与Mg配位态无关的详细振动结构。与溶剂集体振动和局部叶绿素a分子内振动线性耦合强度相关的总Huang-Rhys因子在荧光上等于0.53 +/- 0.07，在吸收上等于0.39 +/- 0.05。电子-声子耦合部分也依赖于非均匀加宽吸收起始带内的激发波长，其平均值S（ph）近似于0.38。所有这些数字都符合弱振动耦合。比较共轭Q(y)吸收光谱和荧光发射光谱以及吸收光谱的温度依赖性，可以明确定位仍有争议的五和六配位叶绿素A物种的Q(x)吸收带位置。这些基本的实验发现得到了半经验量子化学计算的定性支持。
The absorption and fluorescence emission spectra of chlorophyll a in different organic solvents where the central Mg atom is either penta- or hexacoordinated have been studied using conventional and selective spectroscopy methods at ambient and cryogenic temperatures. A breakdown of the basic model mirror-symmetry rule in relation to the lowest-energy Q(y) transitions was observed due to Franck-Condon and Hertzberg-Teller interactions. Detailed vibrational structure in the ground electronic state, virtually independent of the Mg coordination state, was revealed by hole-burning fluorescence line-narrowing technique. The total Huang-Rhys factor associated with the linear vibronic coupling strength of the solvent collective vibrations and the local chlorophyll a intramolecular vibrations is equal to 0.53 +/- 0.07 in fluorescence and to 0.39 +/- 0.05 in absorption. The electron-phonon coupling part was also found to depend on the excitation wavelength within the inhomogeneously broadened absorption origin band, its average value being S(ph)approximate to 0.38. All these numbers qualify for the weak vibronic coupling. A comparison of the conjugate Q(y) absorption and fluorescence emission spectra as well as the temperature dependence of the absorption spectra allowed unambiguous locating of the still controversial Q(x) absorption band position for penta- and hexacoordinated chlorophyll a species. The basic experimental findings have been qualitatively supported by semiempirical quantum chemical calculations.