Shining Light on the Solution- and Excited-State Dynamics of Chalcogenopyrylium Polymethine Dyes
Shining Light on the Solution- and Excited-State Dynamics of Chalcogenopyrylium Polymethine Dyes
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DOI：
10.1021/acs.organomet.2c00263
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发表时间：
2022-08-09
期刊：
影响因子：
2.8
通讯作者：
Cook，Timothy R.
中科院分区：
文献类型：
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作者：
Rosch，Lauren E.;Crawley，Matthew R.;Cook，Timothy R.
尽管人们对硫基吡啶聚甲基染料有了40年的兴趣，但我们对其光物理性质的理解仍然存在重大差距。这些差距阻碍了诸如光动力疗法和/或生物医学传感剂等染料的应用，在这些领域，对其激发态动力学和化学的完整理解是很重要的。例如，尽管以前的报告表明某些染料的单线态氧产率高达12%，但我们没有观察到直接磷光测量中存在102的证据。我们现在通过对14种染料的稳态和脉冲激光动力学实验填补了许多这些空白，其中包括6种新型染料，选择改变物理和电子结构。这些结构变化包括硒和碲杂原子、苯基、噻吩、叔丁基取代基和甲基连接体长度。激发态寿命由飞秒瞬态吸收光谱得到。寿命都低于300ps，表明它们从兴奋状态中迅速放松。值得注意的是，我们没有观察到任何三重态瞬态过程的证据；仅在77 K时观察到磷光。变温核磁共振实验表明，吡喃环在甲基主链上的旋转是这些染料动力学的关键决定因素，这些动力学决定了它们与刚性类似物的光物理区别。我们的工作表明，即使在同一类化合物（例如，吡啶染料）中，性质和反应性也可能存在显著差异，但这些差异的来源仅从光物理测量中并不明显。当与结构动力学研究相结合时，我们已经获得了一个完整的结构-功能关系，我们现在可以应用于更广泛的染料类别，并为开发这些物种的应用奠定了可靠的基础。
Despite 40 years of interest in chalcogenopyrylium polymethine dyes, significant gaps remain in our understanding of their photophysical properties. These gaps hinder efforts to apply such dyes as photodynamic therapy and/or biomedical sensing agents where a complete understanding of their excited-state dynamics and chemistry are important. For example, despite previous reports that establish singlet oxygen yields as high as 12% for certain dyes, we observe no evidence for1O2from direct phosphorescence measurements. We now fill in many of these gaps through steady-state and pulsed-laser kinetic experiments on a family of 14 dyes, including six novel dyes, selected to vary physical and electronic structure. These structural changes encompass the selenium and tellurium heteroatoms, phenyl, thiophene,tert-butyl substituents, and methine linker length. Excited-state lifetimes were obtained by femtosecond transient absorption spectroscopy. Lifetimes were all sub-300 ps, suggesting rapid relaxation out of their excited states. Notably, we observed no evidence of any triplet transient processes; phosphorescence was only observed in samples at 77 K. Variable-temperature NMR experiments implicate rotation of the pyran ring about the methine backbone as a critical determinant of the dynamics of these dyes that distinguishes their photophysics from more rigid analogues. Our work establishes that even within the same class of compounds (e.g., pyrylium dyes), properties and reactivities may differ significantly yet the origins of these differences are not apparent from photophysical measurements alone. When combined with studies of structural dynamics, we have obtained a complete structure–function relationship that we can now apply to much broader classes of dyes and serves as a reliable foundation for developing the applications of such species.