Laboratory for functional and metabolic imaging, LIFMET, Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland.
Laboratory for functional and metabolic imaging, LIFMET, Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland.
J Photochem Photobiol B. 2020 Aug;209:111887. doi: 10.1016/j.jphotobiol.2020.111887. Epub 2020 Apr 30.
Delayed fluorescence (DF) is a long-lived luminescence process used in a variety of applications ranging from oxygen sensing in biological tissues to organic Light Emitting Diodes. In common cases, DF results from the de-excitation of the first excited triplet state via the first excited singlet state of the chromophore, which produces a mono-exponential light signal whose amplitude and lifetime give an insight into the probed environment. However, non-linear de-excitation reactions such as triplet-triplet annihilation, which can cause decays to lose their mono-exponential nature, are often neglected. In this work, we derive a global framework to properly interpret decays resulting from a combination of linear and non-linear de-excitation processes. We show why the standard method of using multi-exponential models when decays are not mono-exponential is not always relevant, nor accurate. First, we explain why the triplet de-excitation and light production processes should be analyzed individually: we introduce novel concepts to precisely describe these two processes, namely the deactivation pathway - the reaction which mainly contributes to the triplet state de-excitation - and the measurement pathway - the reaction which is responsible for light production. We derive explicit fitting functions which allow the experimenter to estimate the reaction rates and excited state concentrations in the system. To validate our formalism, we analyze the in vitro Transient Triplet Absorption and DF of Protoporphyrin IX, a well-known biological aromatic molecule used in photodynamic therapy, cancer photodetection and oxygen sensing, which produces DF through various mechanisms depending on concentration and excitation intensity. We also identify the precise assumptions necessary to conclude that triplet-triplet annihilation DF should follow a mono-exponential decay with a lifetime of half the triplet state lifetime. Finally, we describe why the commonly used definitions of triplet / DF lifetime are ill-defined in the case where second-order reactions contribute to the deactivation process, and why the fitting of precise mixed-orders DF kinetics should be preferred in this case. This work could allow the correct interpretation of various long-lived luminescence processes and facilitate their understanding.
延迟荧光（DF）是一种长寿命发光过程，广泛应用于从生物组织中的氧传感到有机发光二极管等各种领域。在常见情况下，DF 是通过发色团的第一激发单线态使第一激发三重态去激发而产生的，它产生一个单指数光信号，其幅度和寿命可以深入了解被探测的环境。然而，常被忽视的非线性质子转移反应，如三重态-三重态湮灭，可能导致衰减失去其单指数性质。在这项工作中，我们推导出一个全局框架来正确解释由线性和非线性去激发过程组合产生的衰减。我们展示了为什么在衰减不是单指数时使用多指数模型的标准方法并不总是相关且准确的原因。首先，我们解释了为什么必须单独分析三重态去激发和光产生过程：我们引入了新的概念来精确描述这两个过程，即失活途径——主要导致三重态去激发的反应——和测量途径——负责光产生的反应。我们推导出明确的拟合函数，使实验人员能够估计系统中的反应速率和激发态浓度。为了验证我们的形式，我们分析了原卟啉 IX 的体外瞬态三重态吸收和 DF，原卟啉 IX 是一种用于光动力疗法、癌症光检测和氧传感的著名生物芳香族分子，它通过各种机制产生 DF，具体取决于浓度和激发强度。我们还确定了必要的精确假设，以得出结论，认为三重态-三重态湮灭 DF 应该遵循半衰期为三重态寿命一半的单指数衰减。最后，我们描述了为什么在二阶反应对去激发过程有贡献的情况下，通常使用的三重态/DF 寿命定义是不明确的，以及为什么在这种情况下应该优先拟合精确的混合阶 DF 动力学。这项工作可以允许正确解释各种长寿命发光过程，并促进对其的理解。
