纯有机室温磷光由于其独特的长余辉性质, 在数据加密、 防伪、 有机发光二极管以及细胞成像等应用领域引起了广泛关注。 目前, 设计具有高亮磷光和超长发光时间的有机材料仍然是一个巨大的挑战。 基于重原子效应, 设计与合成了一种纯有机室温磷光分子1,4-二溴-2,5-二氟二(9H-咔唑-9-基)苯(BFCzB), 该化合物在日光下为白色粉末, 紫外灯开、 关后发射明亮黄色磷光, 其最大激发波长为366 nm, 对应的最大发射波长为544 nm, 在590和640 nm还存在两处肩峰, 其寿命为103.55 ms, 余辉接近2 s。 为了探讨重原子引入对磷光的影响, 在(TD)DFT(含时密度泛函理论)上进行了理论模拟, 通过模拟计算可得出HOMO/LUMO的带隙仅为0.02 eV, 说明分子易被激发, 通过与相似无卤素化合物的比较, 引入卤素后能带隙的减弱证明重原子的引入有助于促进单线态和三线态间的自旋轨道耦合(SOC)和系间窜越(ISC)。 为进一步探究BFCzB超长磷光的起源, 进行了粉末X射线衍射(XRD)光谱测试以了解分子堆积模型和存在的相互作用。 对于BFCzB分子, 存在3种类型的分子内相互作用, 包括C—Br…π (3.373 1 Å)卤键、 C—Br…N (3.170 5 Å)卤键和C—F…H—C (2.587 7 Å)氢键。 这些相互作用有效地限制了分子的旋转与振动, 进而极大地降低了非辐射驰豫。 此外, BFCzB分子中卤素原子与相邻分子间还存在着众多分子间相互作用。 C—F与相邻分子的咔唑环形成主要的相互作用C—F…H—C (2.527 1 Å)氢键和C—F…π(2.933 5和3.049 4 Å)卤键, Br与相邻分子也存在着C—Br…H—C (2.846 6 Å)氢键和C—Br…π(3.531 4 Å)卤键相互作用。 邻近分子的咔唑基团还存在着π…π堆积(3.399 2 Å)。 所有这些分子内和分子间的相互作用共同抑制分子运动, 进一步抑制了三重态激子的非辐射弛豫, 实现了超长室温磷光。 该工作还通过TMB比色法验证BFCzB分子的磷光在水中猝灭时产生单重态氧(¹O₂), 并基于此进行光动力学抗菌实验。 本研究可为纯有机磷光分子的设计、 合成和应用提供借鉴。

Purely organic room temperature phosphorescence (ORTP), due to its wide Stokes shift, low fabrication cost and unique long after glow emission, has attracted extensive attention in many applications such as data encryption, anti-counterfeiting, organic light emitting diodes and cell imaging. At present, designing organic materials with high phosphorescence and extremely long luminescent time is still a great challenge. Based on the heavy atom effect, a purely ORTP molecule was designed and synthesized in this work. This compound was white powder under ambient conditions, and can emit a bright yellow phosphorescence when the UV lamp was turned on. The maximum excitation at 366 nm, the corresponding maximum emission at 544 nm, and two shoulder peaks at 590 and 640 nm, respectively, were observed. The lifetime was 103.55 ms, and the afterglow was close to 2 s. To explore the influence of heavy atom introduction on phosphorescence, a theoretical simulation was performed by (TD) DFT. The band gap of HOMO/LUMO was only 0.02 eV, which indicated that the molecule was easily excited. Compared with similar halohaline-free compounds, It is proved that the introduction of heavy atoms is helpful in increasing the rate of spin-orbit coupling (SOC) and intersystem crossing (ISC) between singlet and triplet states. XRD spectroscopy was performed to further explore the origin of BFCzB ultralong phosphorescence and investigate the molecular packing model and the presence of interactions. InBFCzB molecules, three types of intramolecular interactions, including C—Br…π (3.373 1 Å) halogen bond, C—Br…N (3.170 5 Å) halogen bond and C—F…H—C (2.587 7 Å) hydrogen bond were observed, which effectively limited the rotation and vibration of the molecules, thereby reducing the non-radiative energy attenuation. In addition, some intermolecular interactions between halogen atoms and adjacent molecules were found in BFCzB. C—F formed major interactions with the carbazole rings of neighboring molecules, C—F…H—C (2.527 1 Å) hydrogen bond and C—F…π (2.933 5 and 3.049 4 Å) halogen bond. C—Br…H—C (2.846 6 Å) hydrogen bond and C—Br…π (3.531 4 Å) halogen bond were also observed between Br and its neighbors. π…π stacking (3.399 2 Å) was found in the carbazole group of the neighboring molecule. These intramolecular and intermolecular interactions worked together to inhibit molecular motion, further reducing the nonradiative attenuation of triplet excitons and achieving ultra-long phosphorescence. Moreover, in this work, the production of singlet oxygen (¹O₂) during phosphorescence of BFCzB molecular quenching in water was verified by the TMB colorimetric method. Therefore, the photodynamic antibacterial were carried out. This study can provide some reference for the design, synthesis and application of purely ORTP molecules.