Photoinduced charge transfer in a conformational switching chlorin dimer-azafulleroid in polar and nonpolar media.
Photoinduced charge transfer in a conformational switching chlorin dimer-azafulleroid in polar and nonpolar media.
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极性和非极性介质中构象转换二聚体-氮杂富勒烯的光诱导电荷转移
作者：
Nikkonen;Moreno Oliva;Muuronen;Helaja
在本研究中，我们合成了一个仿生反应中心模型，即由一个氯二聚体和一个氮杂氟化合物组成的分子三联体，并与相应的只由一个氯单体和氮杂氟化合物组成的分子二元体进行了比较，研究了它的光物理性质。~1H 核磁共振、UV/Vis和荧光光谱表明，在非极性介质中，二聚体氮杂氟在非极性介质中通过氢键折叠成AC2对称的几何构型，导致氯之间产生明显的电子相互作用，而在极性介质中，两个氯偏离接触。飞秒瞬时吸收光谱研究表明，二聚氮杂氟氯在甲苯中的电荷分离态较长，≈为1.6 ns，而相应的氯单体氮杂氟在甲苯中的寿命为≈0.9 ns。在极性介质中，例如苯腈，也观察到类似的电荷分离态，但寿命不可避免地较短：二聚体和单体氯氮杂氟化合物的寿命分别为65和73 ps。纳秒瞬时吸收和单线态氧磷光研究证实，在甲苯中，电荷分离态通过三重态激发态间接衰变到基态，而在苯腈中，观察到直接复合到基态。互补的密度泛函研究表明，在非极性介质中存在两种能量极小构象，即折叠的二聚体氮杂氟；在极性介质中，两种疏水的氯包裹氮杂氟。对前线分子轨道的检测表明，在折叠构象中，由于部分π-π重叠，每个氯上的HOMO是相等的，并且共享，导致共轭π电子离域，而包裹构象缺乏这种稳定性。因此，二聚体较长的电荷分离寿命被电子给体-受体分离距离和通过离域稳定自由基阳离子的作用所合理化。氯素折叠似乎以类似于在自然光合作用反应中心观察到的叶绿素二聚体的方式改变了光物理性质。
In the present study, a biomimetic reaction center model, that is, a molecular triad consisting of a chlorin dimer and an azafulleroid, is synthesized and its photophysical properties are studied in comparison with the corresponding molecular dyad, which consists only of a chlorin monomer and an azafulleroid. As evidenced by1H NMR, UV/Vis, and fluorescence spectroscopy, the chlorin dimer–azafulleroid folds in nonpolar media into aC2‐symmetric geometry through hydrogen bonding, resulting in appreciable electronic interactions between the chlorins, whereas in polar media the two chlorins diverge from contact. Femtosecond transient absorption spectroscopy studies reveal longer charge‐separated states for the chlorin dimer–azafulleroid; ≈1.6 ns in toluene, compared with the lifetime of ≈0.9 ns for the corresponding chlorin monomer–azafulleroid in toluene. In polar media, for example, benzonitrile, similar charge‐separated states are observed, but the lifetimes are inevitably shorter: 65 and 73 ps for the dimeric and monomeric chlorin–azafulleroids, respectively. Nanosecond transient absorption and singlet oxygen phosphorescence studies corroborate that in toluene, the charge‐separated state decays indirectly via the triplet excited state to the ground state, whereas in benzonitrile, direct recombination to the ground state is observed. Complementary DFT studies suggest two energy‐minima conformations, that is, a folded chlorin dimer–azafulleroid, which is present in nonpolar media, and another conformation in polar media, in which the two hydrophobic chlorins wrap the azafulleroid. Inspection of the frontier molecular orbitals shows that in the folded conformation, the HOMO on each chlorin is equivalent and is shared owing to partial π–π overlap, resulting in delocalization of the conjugated π electrons, whereas the wrapped conformation lacks this stabilization. As such, the longer charge‐separated lifetime for the dimer is rationalized by both the electron donor–acceptor separation distance and the stabilization of the radical cation through delocalization. The chlorin folding seems to change the photophysical properties in a manner similar to that observed in the chlorophyll dimer in natural photosynthetic reaction centers.
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影响因子：
2.9
作者：
D'Souza, Francis;Gadde, Suresh;Ito, Osamu
通讯作者：
Ito, Osamu
影响因子：
--
作者：
Thomas Grösser;Maurizio Prato;Vittorio Lucchini;A. Hirsch;F. Wudl
通讯作者：
Thomas Grösser;Maurizio Prato;Vittorio Lucchini;A. Hirsch;F. Wudl
氢键驱动的自组装C2对称二氢卟酚顺二聚体；
影响因子：
3.2
作者：
Taru Nikkonen;Raisa Haavikko;J. Helaja
通讯作者：
J. Helaja
焦叶绿素 a 的共价结合二聚衍生物。
影响因子：
15
作者：
S. Boxer;G. Closs
通讯作者：
G. Closs
第 2 章 – 太阳能转换仿生系统的现状1
DOI：
10.1016/b978-0-12-185880-3.50007-0
发表时间：
1981
期刊：
The Journal of Physical Chemistry
影响因子：
--
作者：
J. Katz;J. Hindman
通讯作者：
J. Hindman