Several recent reports suggest that arylboronic esters can exhibit room temperature phosphorescence (RTP), an optical property that is desirable for applications in security printing, oxygen sensing, and bioimaging. These findings challenged the fundamental notion that heavy elements or changes in orbital symmetry were required for intersystem crossing to occur in organic compounds. As we had not observed long afterglow in the many arylboronic esters we had synthesized over many years, we suspected that the RTP observed in these systems had a simpler explanation: the materials reported were impure. Herein, we synthesized 12 arylboronic esters that were previously reported to show RTP, and carefully purified them by column chromatography, recrystallization, and sublimation. We re-examined their photophysical properties alongside single-crystal X-ray diffraction analysis and detailed theoretical studies. While 4 of the 12 compounds showed long afterglows as crude products, none of them showed persistent RTP after careful purification. We also successfully isolated the impurity 4-amino-3,5-bis(pinacolatoboryl)benzonitrile (2), identifying it as the impurity responsible for inducing delayed fluorescence in 3,5-bis(pinacolatoboryl)benzonitrile (1). Doping 1 with 1.0 mol % 2 led to a persistent afterglow with a lifetime of 67 ms, which is mediated by a dimer charge transfer state. Our findings call for a re-examination of previous studies reporting RTP from arylboronic esters, highlight the importance of careful purification in photophysical research, and provide a practical strategy for designing organic materials with a long afterglow.

最近的几份报告表明，芳基硼酸酯可以在室温下表现出磷光（RTP），这是一种在安全印刷、氧气传感和生物成像等领域非常理想的光学性质。这些发现挑战了有机化合物中发生系间窜跃需要重元素或轨道对称性改变的基本观念。由于我们在多年合成的许多芳基硼酸酯中没有观察到长余晖现象，我们怀疑这些系统中的RTP有更简单的解释：所报告的材料是不纯的。在此，我们合成了12种之前报道显示RTP的芳基硼酸酯，并通过柱色谱法、重结晶和升华等方法仔细地将它们提纯。我们重新检查了它们的光物理性质，并进行了单晶X射线衍射分析和详细的理论研究。虽然这12种化合物中有4种作为粗产物表现出长余晖，但在经过仔细提纯后，没有一种显示持久RTP。我们也成功分离出了杂质4-氨基-3,5-双(正丙酸硼基)苯甲腈（2），将其识别为导致3,5-双(正丙酸硼基)苯甲腈（1）迟滞荧光的杂质。向1中掺杂1.0 mol% 2可以得到持续67毫秒余晖，这是通过二聚体电荷转移态介导的。我们的发现要求重新评估之前有关芳基硼酸酯RTP的研究，并强调了在光物理研究中仔细提纯的重要性，同时也为设计具有长余晖的有机材料提供了一种实用策略。