叔丁基螺芴咪唑类蓝绿光荧光材料的合成及光物理性能研究

Synthesis and Photophysical Properties of Blue-Green Fluorescent Materials of Tert-Butyl Spirofluorene Imidazoles

摘要: 以叔丁基修饰的螺芴咪唑骨架为核心，分别引入二苯胺和二苯基咔唑作为给体单元，设计并合成了两种蓝绿光有机荧光材料DJ-DPA和DJ-CA。本文围绕“非平面骨架构筑–叔丁基空间位阻调控–不同给体结构比较”这一思路，系统研究了两种材料的分子构型、前线轨道分布、吸收发射行为、电化学性质和热稳定性。通过¹H NMR和HRMS对目标化合物结构进行了确认。DFT计算结果表明，DJ-DPA和DJ-CA的LUMO主要分布在咪唑相关骨架上，而HOMO主要分布在芳胺给体及部分咪唑骨架上，说明两种分子均具有一定给体–受体型电子结构特征。在二氯甲烷溶液中，DJ-DPA和DJ-CA的最大发射波长分别为497 nm和488 nm，光致发光量子产率分别为61.17%和68.09%；在固态下，两者的发射峰分别红移至520 nm和512 nm，对应PLQY分别为42.31%和51.67%。固态发射红移和PLQY降低表明凝聚态分子间相互作用对发光行为具有一定影响。与DJ-DPA相比，DJ-CA的发射略有蓝移，同时PLQY更高，推测与二苯基咔唑给体较大的空间扭转和较强的骨架刚性有关。循环伏安测试表明，DJ-CA具有更深的HOMO能级和更高的氧化电位，说明咔唑给体的引入降低了分子的失电子能力，并与其吸收、发射蓝移现象相互对应。热重分析结果显示，两种材料均具有一定热稳定性。综合结果表明，叔丁基螺芴咪唑骨架能够为分子提供非平面空间结构和一定电子调控能力，不同给体单元则进一步影响材料的电荷转移程度、发光效率、电化学性质和热稳定性。本研究可为螺芴咪唑类蓝绿光有机荧光材料的结构设计提供参考。

Abstract: A tert-butyl-modified spirofluorene-imidazole core was employed as the central skeleton, into which diphenylamine and diphenylcarbazole were introduced as donor units, leading to the design and synthesis of two blue-green organic fluorescent materials, namely DJ-DPA and DJ-CA. Following the concept of “non-planar skeleton construction - steric hindrance modulation by tert-butyl groups - comparison of different donor structures”, this study systematically investigated the molecular configurations, frontier orbital distributions, absorption and emission behaviors, electrochemical properties, and thermal stabilities of the two materials. The structures of the target compounds were confirmed by ¹H NMR and HRMS. DFT calculations revealed that the LUMOs of DJ-DPA and DJ-CA are predominantly localized on the imidazole-related skeleton, while the HOMOs are mainly distributed over the arylamine donors and part of the imidazole skeleton, indicating that both molecules exhibit distinct donor - acceptor electronic characteristics. In dichloromethane solution, DJ-DPA and DJ-CA exhibit maximum emission wavelengths of 497 nm and 488 nm, with photoluminescence quantum yields (PLQYs) of 61.17% and 68.09%, respectively. In the solid state, their emission peaks redshift to 520 nm and 512 nm, accompanied by decreased PLQY values of 42.31% and 51.67%, respectively. These spectral redshifts and PLQY reductions upon aggregation suggest that intermolecular interactions in the condensed phase exert a notable influence on the photoluminescent behavior. Compared with DJ-DPA, DJ-CA exhibited a slight blue shift in emission and a higher PLQY, which is attributed to the larger torsional conformation and enhanced backbone rigidity of the diphenylcarbazole donor. Cyclic voltammetry measurements indicated that DJ-CA possesses a deeper HOMO level and a higher oxidation potential, suggesting that the introduction of the carbazole donor reduces the electron-donating ability of the molecule, which is consistent with the observed blue shifts in absorption and emission. Thermogravimetric analysis demonstrated that both materials possess satisfactory thermal stability. Collectively, these results confirm that the tert-butyl spirofluorene-imidazole skeleton endows the molecules with a non-planar spatial structure and a certain capacity for electronic modulation, while the different donor units further influence the degree of charge transfer, luminescence efficiency, electrochemical properties, and thermal stability of the materials. This study provides a useful reference for the structural design of spirofluorene-imidazole- based blue-green organic fluorescent materials.