Triplet formation involving a polar transition state in a well-defined intramolecular perylenediimide dimeric aggregate.
Triplet formation involving a polar transition state in a well-defined intramolecular perylenediimide dimeric aggregate.
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DOI：
10.1021/jp8022524
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发表时间：
2008-06
期刊：
影响因子：
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通讯作者：
D. Veldman;Stéphanie M A Chopin;S. Meskers;Michiel M. Groeneveld;René M. Williams;R. Janssen
中科院分区：
文献类型：
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作者：
D. Veldman;Stéphanie M A Chopin;S. Meskers;Michiel M. Groeneveld;René M. Williams;R. Janssen
在各种条件下（溶剂，温度）的cofacially堆叠的苝二酰亚胺（PDI）二聚体与氧杂蒽接头进行了研究，并作为一个模型的分子间的相互作用发生在固体薄膜。本质上，PDI单元具有接近1的荧光量子产率（Phi F），但是当两个PDI部分保持共面排列时，Phi F在室温下降低6-50倍，而与单体PDI分子（tau F = 4 ns）相比，最大发射状态的衰减时间显著增加（在甲苯中tau F = 27 ns）。荧光测量显示了强溶剂和温度依赖性的发射激发态的特性。在甲苯（TOL）或2-甲基四氢呋喃（2-MeTHF）的玻璃基质中，Phi F高，并且衰减时间长（τ F =约50 ns）。在较高的温度下，Phi F和tau F都降低。有趣的是，在室温下，Phi F和tau F也随着溶剂极性的增加而减少，揭示了极性过渡态的存在。从皮秒到微秒时间尺度的堆叠分子的光诱导吸收表明，在光激发后，在第一纳秒发生重组，随后发生系间交叉（ISC），产生三重激发态。以单重态氧（1）Δ g发光为探针，在空气饱和的2-Me-THF中获得了大于50%的三重态量子产率（Phi-T）。三重态的形成是例外的PDI发色团，和增强的ISC是由涉及一个高极性过渡态的衰减解释。
A cofacially stacked perylenediimide (PDI) dimer with a xanthene linker was studied under a variety of conditions (solvent, temperature) and serves as a model for the molecular interactions occurring in solid films. Intrinsically, the PDI units have a fluorescence quantum yield (Phi F) close to unity, but Phi F is lowered by a factor of 6-50 at room temperature when two PDI moieties are held in a cofacial arrangement, while the decay time of the most emissive state is increased significantly (tau F = 27 ns in toluene) compared to a monomeric PDI molecule (tau F = 4 ns). Fluorescence measurements show a strong solvent and temperature dependence of the characteristics of the emissive excited state. In a glassy matrix of toluene (TOL) or 2-methyltetrahydrofuran (2-MeTHF), Phi F is high, and the decay time is long (tau F = approximately 50 ns). At higher temperature, both Phi F and tau F are reduced. Interestingly, at room temperature, Phi F and tau F are also reduced with increasing solvent polarity, revealing the presence of a polar transition state. Photoinduced absorption of the stacked molecules from the picosecond to the microsecond time scale shows that after photoexcitation reorganization occurs in the first nanoseconds, followed by intersystem crossing (ISC), producing the triplet excited state. Using singlet oxygen ( (1)Delta g) luminescence as a probe, a triplet quantum yield (Phi T) greater than 50% was obtained in air-saturated 2-Me-THF. Triplet formation is exceptional for PDI chromophores, and the enhanced ISC is explained by a decay involving a highly polar transition state.