Self-trapped excitons in LH2 antenna complexes between 5 K and ambient temperature
Self-trapped excitons in LH2 antenna complexes between 5 K and ambient temperature
复制标题
DOI：
10.1021/jp0344848
复制
发表时间：
2003-10-16
影响因子：
3.3
通讯作者：
Woodbury, NW
中科院分区：
文献类型：
--
作者：
Freiberg, A;Rätsep, M;Woodbury, NW
研究了光合紫色细菌Rhodobacter sphaeroides的LH 2复合物中激子的高光谱分辨率烧孔和荧光谱线窄化光谱，以及传统的宽带荧光光谱及其温度依赖性。稳态光谱已经补充了荧光寿命测量，实验结果进行了讨论的基础上的绝热Holstein激子极化子模型，修改包括对角无序。这一结果为LH 2天线光谱提供了一种新的解释。当光激发时，激子在弛豫后变得局域化。LH 2荧光主要是由于自陷激子，不仅在低温下，如先前所建议的（Timpmann，K.; Katiliene，Z.;伍德伯里，N. W的;弗赖贝格，A. J. Phys. Chem. B 2001，105，12223），而且在直到生理温度的整个温度范围内，因为自陷激子结合能与环境温度下的热激发能具有相同的数量级。结果表明，直接自陷弛豫在激子态间的共能弛豫中占主导地位，限制弛豫激子尺寸的主要因素是动态无序而不是静态无序。大、小激子极化子在低温下共存的现象已得到证实。激子自陷也基本上修改了LH 2复合物的吸收光谱的长波长尾部。受烧孔影响的吸收光谱的部分是由于与晶格弱耦合的大半径自陷激子。在烧孔中幸存的光谱的其余部分属于强耦合的自陷激子/准分子。斯塔克光谱实验的解释，以及对光合能量转移和捕获这些结果的影响进行了讨论。
High-spectral-resolution hole-burning and fluorescence line-narrowing spectra of excitons in LH2 complexes from the photosynthetic purple bacterium Rhodobacter sphaeroides have been investigated together with conventional broadband fluorescence spectra and their temperature dependence. The steady-state spectroscopy has been complemented by fluorescence lifetime measurements, The experimental results are discussed on the basis of the adiabatic Holstein exciton polaron model, modified by including diagonal disorder. As a result, a new interpretation for the LH2 antenna optical spectra is provided. The exciton when optically excited becomes localized after relaxation. The LH2 fluorescence is mainly due to self-trapped excitons not only at low temperature, as previously suggested (Timpmann, K.; Katiliene, Z.; Woodbury, N. W.; Freiberg, A. J. Phys. Chem. B 2001, 105, 12223), but also over the whole temperature range up to physiological temperatures because the self-trapped exciton binding energy is of the same order as the thermal excitation energy at ambient temperature. The conclusion is made that direct self-trapping relaxation dominates the common energy relaxation between exciton states and that the main factor limiting the relaxed exciton size is dynamic rather than static disorder. The coexistence of large and small exciton polarons at low temperatures has been confirmed. Exciton self-trapping also essentially modifies the long-wavelength tail of the absorption spectrum of LH2 complexes. The fraction of the absorption spectrum that is subject to hole burning is due to large-radius self-trapped excitons that are weakly coupled to the lattice. The rest of this spectrum that survives hole burning belongs to the strongly coupled self-trapped excitons/excimers. Implications of these results on the interpretation of Stark spectroscopy experiments as well as on photosynthetic energy transfer and trapping are discussed.