螺芴咪唑–咔唑位点异构体的光物理性质及发光效率差异研究

Photophysical Properties and Luminescence Efficiency Differences of Spirofluorene-Imidazole/Carbazole Positional Isomers

摘要: 为探究连接位点对螺芴咪唑–咔唑类有机荧光材料发光行为的影响，本文以螺芴咪唑为核心骨架、二苯基咔唑为给体单元，设计并合成了两种位点异构型蓝绿光荧光材料DP-CA和SP-CA。两种化合物组成单元相同，但给体连接位置不同，可作为研究位点异构效应的模型分子。通过¹H NMR和HRMS对目标化合物结构进行了确认，并结合DFT计算、紫外–可见吸收光谱、荧光光谱、时间分辨荧光、循环伏安法和热重分析系统研究其结构与性能关系。结果表明，DP-CA和SP-CA均表现出蓝绿光发射，最大发射波长分别为498 nm和489 nm，但其光致发光量子产率差异显著，分别为81.52%和5.11%。时间分辨荧光测试显示，二者积分寿命分别为10.46 ns和10.69 ns，说明发光效率差异并非主要由激发态寿命决定，而与辐射跃迁效率及非辐射失活过程密切相关。DFT计算表明，DP-CA中给体与受体之间保持适度电子耦合，有利于辐射跃迁；而SP-CA中HOMO/LUMO空间分离程度较高，可能削弱辐射跃迁并增强非辐射失活，从而导致PLQY明显降低。热重分析显示，SP-CA的热分解温度为540℃，高于DP-CA的434℃，表明热稳定性与发光效率并不必然同步。上述结果说明，连接位点不仅影响螺芴咪唑–咔唑类材料的分子构型和能级分布，还会调控轨道重叠及辐射/非辐射过程的竞争关系，为位点异构调控蓝绿光有机荧光材料性能提供了参考。

Abstract: To investigate the influence of connection sites on the luminescence behavior of spirofluorene-imidazole/carbazole-based organic fluorescent materials, two positional isomeric blue-green fluorescent materials, DP-CA and SP-CA, were designed and synthesized using spirofluorene-imidazole as the core skeleton and diphenylcarbazole as the donor unit. The two compounds possess identical structural units but differ in the donor connection sites, making them suitable model molecules for studying positional isomerism effects. The structures of the target compounds were confirmed by ¹H NMR and HRMS, and their structure-property relationships were systematically investigated by DFT calculations, UV-vis absorption spectroscopy, photoluminescence spectroscopy, time-resolved fluorescence measurements, cyclic voltammetry, and thermogravimetric analysis. The results show that both DP-CA and SP-CA exhibit blue-green emission, with maximum emission wavelengths of 498 nm and 489 nm, respectively. However, their photoluminescence quantum yields differ significantly, reaching 81.52% and 5.11%, respectively. Time-resolved fluorescence measurements reveal that their integrated lifetimes are 10.46 ns and 10.69 ns, indicating that the difference in luminescence efficiency is not mainly determined by the excited-state lifetime, but is closely related to radiative transition efficiency and nonradiative decay processes. DFT calculations indicate that DP-CA maintains moderate electronic coupling between the donor and acceptor units, which is favorable for radiative transition, whereas SP-CA exhibits a higher degree of HOMO/LUMO spatial separation, which may weaken radiative transition and enhance nonradiative decay, resulting in a markedly reduced PLQY. Thermogravimetric analysis shows that the decomposition temperature of SP-CA is 540˚C, higher than that of DP-CA at 434˚C, suggesting that thermal stability and luminescence efficiency are not necessarily correlated. These results demonstrate that the connection site not only affects the molecular configuration and energy-level distribution of spirofluorene-imidazole/carbazole-based materials, but also regulates orbital overlap and the competition between radiative and nonradiative processes, providing a reference for tuning the performance of blue-green organic fluorescent materials through positional isomerism.