Institute of Organic Chemistry, Technische Universität Braunschweig, Hagenring 30, 38106 Braunschweig, Germany.
Institute of Physical and Theoretical Chemistry, Universität Würzburg, Emil-Fischer-Straße 42, 97074 Würzburg, Germany.
J Am Chem Soc. 2021 May 19;143(19):7414-7425. doi: 10.1021/jacs.1c01279. Epub 2021 May 6.
A series of distinct BODIPY heterooligomers (dyads, triads, and tetrads) comprising a variable number of typical BODIPY monomers and a terminal red-emitting styryl-equipped species acting as an energy sink was prepared and subjected to computational and photophysical investigations in solvent media. An ethylene tether between the single monomeric units provides a unique foldameric system, setting the stage for a systematic study of excitation energy transfer processes (EET) on the basis of nonconjugated oscillators. The influence of stabilizing β-ethyl substituents on conformational space and the disorder of site energies and electronic couplings was addressed. In this way both the strong (Frenkel) and the weak (Förster) coupling limit could be accessed within a single system: the Frenkel limit within the strongly coupled homooligomeric donor subunit and the Förster limit at the terminal heterosubstituted ethylene bridge. Femtosecond transient-absorption spectroscopy combined with mixed quantum-classical dynamic simulations demonstrate the limitations of the Förster resonance energy transfer (FRET) theory and provide a consistent framework to elucidate the trend of increasing relaxation lifetimes at higher homologues, revealing one of the fastest excitation energy transfer processes detected to date with a corresponding lifetime of 39 fs.
一系列不同的 BODIPY 杂寡聚物（二聚体、三聚体和四聚体）由可变数量的典型 BODIPY 单体和一个末端发射红光的苯乙烯取代基组成，作为能量汇，在溶剂介质中进行了计算和光物理研究。单体单元之间的乙烯系绳提供了独特的折叠体系统，为基于非共轭振荡器的激发能量转移过程（EET）的系统研究奠定了基础。稳定的 β-乙基取代基对构象空间和位置能量和电子耦合的无序的影响得到了研究。通过这种方式，在单个系统中可以同时访问强（Frenkel）和弱（Förster）耦合极限：强耦合同寡聚供体亚基内的 Frenkel 极限和末端杂取代乙烯桥的 Förster 极限。飞秒瞬态吸收光谱结合混合量子经典动力学模拟证明了Förster 共振能量转移（FRET）理论的局限性，并提供了一个一致的框架来阐明在更高同系物中增加弛豫寿命的趋势，揭示了迄今为止检测到的最快的激发能量转移过程之一，相应的寿命为 39 fs。
