Structural control of the photodynamics of boron-dipyrrin complexes
Structural control of the photodynamics of boron-dipyrrin complexes
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DOI：
10.1021/jp0525078
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发表时间：
2005-11-03
影响因子：
3.3
通讯作者：
Holten, D
中科院分区：
文献类型：
--
作者：
Kee, HL;Kirmaier, C;Holten, D
合成了含有5-芳基的硼-二吡咯发色团，其具有或不具有对芳基旋转的内部空间位阻，然后通过X射线衍射，静态和时间分辨光谱和理论进行表征。具有5-苯基或5-（4-叔丁基苯基）基团的化合物显示出低的荧光产率（类似于0.06）和短的激发单重态寿命（类似于500 ps），并且主要通过非辐射内转换到基态而衰减（> 90%）。相比之下，在5位具有邻甲苯基或均三甲苯基的空间位阻类似物表现出高荧光产率（类似于0.9）和长激发态寿命（类似于6 ns）。X-射线结构表明，苯基或4-叔丁基苯基环相对于二吡咯骨架以类似于60度的角度存在，而对于均三甲苯基或邻甲苯基，该角度类似于80度。计算的势能面的苯基取代的配合物表明，激发态具有第二个，较低的能量最小值，其中无阻碍的芳基环旋转更接近的平均平面的二吡咯，这本身经历了一些扭曲。这种松弛的，扭曲的激发态构象具有低辐射概率以及从基态支持有利的振动重叠因子的非辐射失活的减少的能隙。这种扭曲的构象在5-位上具有空间位阻的邻甲苯基或均三甲苯基的复合物中是能量上不可接近的，导致涉及处于或接近激发态的初始弗兰克-康登形式的构象的高辐射概率。这些结合的结果表明，芳基环旋转在管理这类广泛使用的染料的激发态动力学的关键作用。
Boron-dipyrrin chromophores containing a 5-aryl group with or without internal steric hindrance toward aryl rotation have been synthesized and then characterized via X-ray diffraction, static and time-resolved optical spectroscopy, and theory. Compounds with a 5-phenyl or 5-(4-tert-butylphenyl) group show low fluorescence yields (similar to 0.06) and short excited-singlet-state lifetimes (similar to 500 ps), and decay primarily (> 90%) by nonradiative internal conversion to the ground state. In contrast, sterically hindered analogues having an o-tolyl or mesityl group at the 5-position exhibit high fluorescence yields (similar to 0.9) and long excited-state lifetimes (similar to 6 ns). The X-ray structures indicate that the phenyl or 4-tert-butylphenyl ring lies at an angle of similar to 60 degrees with respect to the dipyrrin framework whereas the angle is similar to 80 degrees for mesityl or o-tolyl groups. The calculated potential energy surface for the phenyl-substituted complex indicates that the excited state has a second, lower energy minimum in which the nonhindered aryl ring rotates closer to the mean plane of the dipyrrin, which itself undergoes some distortion. This relaxed, distorted excited-state conformation has low radiative probability as well as a reduced energy gap from the ground state supporting a favorable vibrational overlap factor for nonradiative deactivation. Such a distorted conformation is energetically inaccessible in a complex bearing the sterically hindered o-tolyl or mesityl group at the 5-position, leading to a high radiative probability involving conformations at or near the initial Franck-Condon form of the excited state. These combined results demonstrate the critical role of aryl-ring rotation in governing the excited-state dynamics of this class of widely used dyes.