Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, Institute of Materials and Clean Energy, School of Physics and Electronics, Shandong Normal University, Jinan 250014, China.
School of Science, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, China.
Phys Chem Chem Phys. 2023 Mar 1;25(9):6659-6673. doi: 10.1039/d2cp05743c.
Organic room temperature phosphorescence (RTP) has been widely investigated to realize long-lifetime luminescent materials and improvement in their efficiency is a key focus of research, especially for red and near-infrared (NIR) RTP molecules. However, due to the lack of systematic studies on the relationship between basic molecular structures and luminescence properties, both the species and amounts of red and NIR RTP molecules remain far from meeting the requirements of practical applications. Herein, based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations, the photophysical properties of seven red and NIR RTP molecules in tetrahydrofuran (THF) and in the solid phase were theoretically studied. The excited state dynamic processes were investigated by calculating the intersystem crossing and reverse intersystem crossing rates considering the surrounding environmental effects in THF and in the solid phase using a polarizable continuum model (PCM) and quantum mechanics and molecular mechanics (QM/MM) method, respectively. The basic geometric and electronic data were obtained, Huang-Rhys factors and reorganization energies were analyzed, and natural atomic orbital was used to calculate the orbital information of the excited states. Simultaneously, the electrostatic potential distribution on molecular surfaces was analyzed. Further, intermolecular interactions were visualized using the molecular planarity binding independent gradient model based on Hirshfeld partition (IGMH). The results showed that the unique molecular configuration has the potential to achieve red and NIR RTP emission. Not only did the substitutions of halogen and sulfur make the emission wavelength red-shifted, but also linking the two cyclic imide groups could further make the emission wavelength longer. Moreover, we found that the emission characteristics of molecules in THF had a similar trend as in the solid phase. Based on this point, two new RTP molecules with long emission wavelengths (645 nm and 816 nm) are theoretically proposed and their photophysical properties are fully analyzed. Our investigation provides a wise strategy to design efficient and long-emission RTP molecules with an unconventional luminescence group.
有机室温磷光（RTP）已被广泛研究，以实现长寿命发光材料，提高其效率是研究的关键焦点，特别是对于红色和近红外（NIR）RTP 分子。然而，由于缺乏对基本分子结构与发光性能之间关系的系统研究，红色和 NIR RTP 分子的种类和数量仍远远不能满足实际应用的要求。在此，基于密度泛函理论（DFT）和含时密度泛函理论（TD-DFT）计算，从理论上研究了七种红色和 NIR RTP 分子在四氢呋喃（THF）和固相中的光物理性质。通过计算考虑 THF 和固相中环境影响的体系间窜越和反向体系间窜越速率，研究了激发态动力学过程，分别采用极化连续体模型（PCM）和量子力学和分子力学（QM/MM）方法。得到了基本的几何和电子数据，分析了 Huang-Rhys 因子和重组能，并用自然原子轨道计算了激发态的轨道信息。同时，分析了分子表面的静电势能分布。此外，基于 Hirshfeld 分割（IGMH）的分子平面结合独立梯度模型（IGMH）可视化了分子间相互作用。结果表明，独特的分子构型有可能实现红色和 NIR RTP 发射。卤素和硫的取代不仅使发射波长红移，而且连接两个环状酰亚胺基团可以进一步使发射波长变长。此外，我们发现分子在 THF 中的发射特性与在固相中的趋势相似。基于这一点，理论上提出了两种具有长发射波长（645nm 和 816nm）的新型 RTP 分子，并对其光物理性质进行了全面分析。我们的研究为设计具有非常规发光基团的高效长发射 RTP 分子提供了明智的策略。
