Visible-Light-Driven Triplet Sensitization of Polycyclic Aromatic Hydrocarbons Using Thionated Perinones
Visible-Light-Driven Triplet Sensitization of Polycyclic Aromatic Hydrocarbons Using Thionated Perinones
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DOI：
10.1021/acs.jpclett.0c01634
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发表时间：
2020-07-02
影响因子：
5.7
通讯作者：
Castellano, Felix N.
中科院分区：
文献类型：
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作者：
Palmer, Jonathan R.;Wells, Kaylee A.;Castellano, Felix N.
有效产生三重态激发态的无金属发色团代表了相对于含过渡金属光敏剂的有希望的替代品，例如那些具有金属到配体电荷转移激发态的光敏剂。然而，由于分子结构与高效/快速系统间交叉之间的关系尚不清楚，这种分子结构仍未得到充分探索。在这方面，我们提出了一系列的三个硫离子的会酮发色团作为一个新构想的一类无重金属三重态光敏剂。我们证明，在每个高荧光perinone中，单个C=O取代基的硫代化带来了红移吸收带，在可见光谱中保持强烈的消光系数，以及从测量的单线态O-2量子产率推断的异常高效的三重态激发态形成在1270 nm （Phi(Delta) = 0.78-1.0）。电子结构计算表明，在能量稍高的S-2 （pi -> pi*）激发态附近出现了低能S-1 （n -> pi*）激发态。由于电子交换相互作用的不同，这两个最底层单重态流形的不同特性导致了相应的三重态激发态的能量反转。因此，通过El Sayed规则预测的自旋-轨道耦合，以这种方式促进了S-1 -> - T-1系统间的快速交叉。由此产生的三重态激发态的寿命持续到微秒时间范围，通过瞬态吸收光谱测量，使一些常见的多环芳烃的有效的双分子三重态敏化成为可能。在所研究的会酮中，单个O原子与S原子的合成交换导致了它们的光物理性质的显著变化，即前者的优势单重态荧光转化为后者的长寿命三重态激发态。综合结果表明，在结构中存在单个C=O基团的有机发色团中获得长寿命三重态激发态的一般策略，对设计无金属三重态光敏剂有价值。
Metal-free chromophores that efficiently generate triplet excited states represent promising alternatives with respect to transition metal-containing photosensitizers, such as those featuring metal-to-ligand charge transfer excited states. However, such molecular constructs have remained underexplored due to the unclear relationship(s) between molecular structure and efficient/rapid intersystem crossing. In this regard, we present a series of three thionated perinone chromophores serving as a newly conceived class of heavy metal-free triplet photosensitizers. We demonstrate that thionation of the lone C=O substituent in each highly fluorescent perinone imparts red-shifted absorbance bands that maintain intense extinction coefficients across the visible spectrum, as well as unusually efficient triplet excited state formation as inferred from the measured singlet O-2 quantum yields at 1270 nm (Phi(Delta) = 0.78-1.0). Electronic structure calculations revealed the emergence of a low energy S-1 (n -> pi*) excited state in the proximity of a slightly higher energy S-2 (pi -> pi*) excited state. The distinct character in each of the two lowest-lying singlet state manifolds resulted in the energetic inversion of the corresponding triplet excited states due to differences in electron exchange interactions. Rapid S-1 -> T-1 intersystem crossing was thereby facilitated in this manner through spin-orbit coupling as predicted by the El Sayed rules. The lifetimes of the resultant triplet excited states persisted into the microsecond time regime, as measured by transient absorbance spectroscopy, enabling effective bimolecular triplet sensitization of some common polycyclic aromatic hydrocarbons. The synthetically facile interchange of a single O atom to an S atom in the investigated perinones resulted in marked changes to their photophysical properties, namely, conversion of dominant singlet state fluorescence in the former to long-lived triplet excited states in the latter. The combined results suggest a general strategy for accessing long-lived triplet excited states in organic chromophores featuring a lone C=O moiety residing within its structure, valuable for the design of metal-free triplet photosensitizers.