Dhali Rama, Phan Huu D K Andrea, Bertocchi Francesco, Sissa Cristina, Terenziani Francesca, Painelli Anna
Department of Chemistry, Life Science and Environmental Sustainability, University of Parma, 43124 Parma, Italy.
Phys Chem Chem Phys. 2021 Jan 6;23(1):378-387. doi: 10.1039/d0cp05982j.
Thermally-activated delayed fluorescence (TADF) is a promising strategy to harvest triplets in OLED towards improved efficiency, but several issues must be addressed to fully exploit its potential, including the nature of involved excited singlet and triplet states and their response to the local environment in order to concurrently optimize the dye inside the matrix. Towards this ambitious aim, we present an extensive spectroscopic study of a typical TADF dye in liquid and glassy solvents. TD-DFT results for the same molecule in gas-phase and under an applied electric field are exploited to build a reliable model for the dye, rigorously validated against experiment. The model, accounting for charge transfer and local singlet and triplet states, spin-orbit coupling, conformational and vibrational degrees of freedom, sets the basis for a sound understanding of the photophysics of TADF dyes in different environments. The charge-transfer nature of the fluorescent state and of the almost degenerate phosphorescent state is unambiguously demonstrated. The concurrent role played by conformational degrees of freedom and the matrix polarizability in governing TADF is addressed.
热激活延迟荧光（TADF）是一种在有机发光二极管（OLED）中捕获三线态以提高效率的有前景的策略，但要充分发挥其潜力，必须解决几个问题，包括所涉及的激发单重态和三重态的性质及其对局部环境的响应，以便同时优化基质中的染料。为了实现这一宏伟目标，我们对一种典型的TADF染料在液态和玻璃态溶剂中进行了广泛的光谱研究。利用该分子在气相和外加电场下的含时密度泛函理论（TD-DFT）结果构建了一个可靠的染料模型，并通过实验进行了严格验证。该模型考虑了电荷转移以及局部单重态和三重态、自旋轨道耦合、构象和振动自由度，为深入理解不同环境下TADF染料的光物理性质奠定了基础。明确证明了荧光态和几乎简并的磷光态的电荷转移性质。探讨了构象自由度和基质极化率在控制TADF过程中所起的协同作用。
