Cavendish Laboratory, University of Cambridge , Cambridge CB3 0HE, United Kingdom.
Institute of Materials Research and Engineering, Agency for Science Technology and Research (A*STAR) , 2 Fusionoplis Way, Singapore 138634, Singapore.
J Am Chem Soc. 2017 Dec 20;139(50):18376-18385. doi: 10.1021/jacs.7b10762. Epub 2017 Dec 5.
Singlet fission offers the potential to overcome thermodynamic limits in solar cells by converting the energy of a single absorbed photon into two distinct triplet excitons. However, progress is limited by the small family of suitable materials, and new chromophore design principles are needed. Here, we experimentally vindicate the design concept of diradical stabilization in a tunable family of functionalized zethrenes. All molecules in the series exhibit rapid formation of a bound, spin-entangled triplet-pair state TT. It can be dissociated by thermally activated triplet hopping and exhibits surprisingly strong emission for an optically "dark" state, further enhanced with increasing diradical character. We find that the TT excited-state absorption spectral shape correlates with the binding energy between constituent triplets, providing a new tool to understand this unusual state. Our results reveal a versatile new family of tunable materials with excellent optical and photochemical properties for exploitation in singlet fission devices.
单重态裂变有望通过将单个吸收光子的能量转化为两个不同的三重态激子来克服太阳能电池中的热力学限制。然而，进展受到合适材料种类的限制，需要新的发色团设计原则。在这里，我们通过一系列功能化的薁验证了自由基稳定的设计概念。该系列中的所有分子都表现出快速形成束缚的、自旋纠缠的三重态对 TT 态。它可以通过热激活的三重态跃迁来离解，并表现出令人惊讶的强的光“暗”态发射，随着自由基特性的增加进一步增强。我们发现 TT 激发态吸收光谱形状与组成三重态之间的结合能相关，为理解这种不寻常的状态提供了新的工具。我们的结果揭示了一类具有优异的光学和光化学性质的新型可调谐材料，可用于单重态裂变器件。
