Novel Conjugated s-Tetrazine Derivatives Bearing a 4H-1,2,4-Triazole Scaffold: Synthesis and Luminescent Properties

A series of new symmetrical s-tetrazine derivatives, coupled via a 1,4-phenylene linkage with a 4H-1,2,4-triazole ring, were obtained. The combination of these two rings in an extensively coupled system has significant potential applications, mainly in optoelectronics. The methodology used turned out to be useful regardless of the type of five-membered ring or the nature of the individual substituents. All the products were identified by spectroscopic methods, and the target compounds were tested for luminescent properties. This study showed that all the synthesized highly-conjugated triazoles exhibited luminescence; in particular, one derivative, 3,6-bis(4-(5-(4-methoxyphenyl)-4-phenyl-4H-1,2,4-triazol-3-yl)phenyl)-1,2,4,5-tetrazine (13b), showed strong fluorescence emission and ahigh quantum yield close to 1.     

Synthesis and Luminescent Properties of s-Tetrazine Derivatives Conjugated with the 4H-1,2,4-Triazole Ring

New derivatives obtained by the combination of unique 1,2,4,5-tetrazine and 4H-1,2,4-triazole rings have great application potential in many fields. Therefore, two synthetic few-step methodologies, which make use of commercially available 4-cyanobenzoic acid (method A) and ethyl diazoacetate (method B), were applied to produce two groups of the aforementioned heterocyclic conjugates. In both cases, the target compounds were obtained in various combinations, by introducing electron-donating or electron-withdrawing substituents into the terminal rings, together with aromatic or aliphatic substituents on the triazole nitrogen atom. Synthesis of such designed systems made it possible to analyze the influence of individual elements of the structure on the reaction course, as well as the absorption and emission properties. The structure of all products was confirmed by conventional spectroscopic methods, and their luminescent properties were also determined.     

Enhancing Magnetic Communication between Metal Centres: The Role of s-Tetrazine Based Radicals as Ligands

Although 1,2,4,5-tetrazines or s-tetrazines have been known in the literature for more than a century, their coordination chemistry has become increasingly popular in recent years due to their unique redox activity, multiple binding sites and their various applications. The electron-poor character of the ring and stabilization of the radical anion through all four nitrogen atoms in their metal complexes provide new aspects in molecular magnetism towards the synthesis of new high performing Single Molecule Magnets (SMMs). The scope of this review is to examine the role of s-tetrazine radical ligands in transition metal and lanthanide based SMMs and provide a critical overview of the progress thus far in this field. As well, general synthetic routes and new insights for the preparation of s-tetrazines are discussed, along with their redox activity and applications in various fields. Concluding remarks along with the limitations and perspectives of these ligands are discussed.     

一种新型含能材料s-四嗪钴盐的合成、热分解动力学及热安全性

四嗪类含能化合物因其高能、钝感、高燃速、低压力指数、良好的热安定性等特点被广泛应用于含能材料领域。然而却存在低密度、低热稳定性的问题,为提高四嗪类化合物的这一性能,制备的一系列金属衍生物得到了广泛关注。3,6-双(1-氢-1,2,3,4-四唑-5-氨基)-1,2,4,5-四嗪(BTATz)作为四嗪类高氮含能化合物一种,具有良好的催化性能及应用前景。本文以BTATz钾与硝酸钴在水溶液中反应合成了1,2,4,5-四嗪(s-四嗪)的钴盐。采用元素分析(EA)、傅里叶变换红外光谱分析(FTIR)及电感耦合等离子体质谱(ICP-MS)对其进行了结构表征,推测其化学式为Co(C_4H_2N_(14))·4H_2O。采用差示扫描量热仪(DSC)和热重分析仪(TG/DTG)研究了其热分解行为及主放热反应的动力学方程。计算了自加速分解温度(T_(SADT))、热爆炸临界温度(T_b)、热点火温度(T_(TIT))和绝热至爆时间(t_(TIAD)),其值分别为509.69 K、556.31 K、524.93 K和88.40 s,并以此来评价化合物的热安全性。该金属盐的绝热至爆时间大于相应的Ca盐、Mg盐和Sr盐,放热量高于配体BTATz,有望成为良好的燃烧催化剂。     

Redox Potential Tuning of s-Tetrazine by Substitution of Electron-Withdrawing/Donating Groups for Organic Electrode Materials

Herein, we tune the redox potential of 3,6-diphenyl-1,2,4,5-tetrazine (DPT) by introducing various electron-donating/withdrawing groups (methoxy, t-butyl, H, F, and trifluoromethyl) into its two peripheral benzene rings for use as electrode material in a Li-ion cell. By both the theoretical DFT calculations and the practical cyclic voltammetry (CV) measurements, it is shown that the redox potentials (E_1/2) of the 1,2,4,5-tetrazines (s-tetrazines) have a strong correlation with the Hammett constant of the substituents. In Li-ion coin cells, the discharge voltages of the s-tetrazine electrodes are successfully tuned depending on the electron-donating/withdrawing capabilities of the substituents. Furthermore, it is found that the heterogeneous electron transfer rate (k₀) of the s-tetrazine molecules and Li-ion diffusivity (D_Li) in the s-tetrazine electrodes are much faster than conventional electrode active materials.     

s-四嗪-水簇复合物的理论研究

用量子化学B3LYP方法和6-31＋＋G**基函数研究了s-四嗪-水簇复合物基态分子间相互作用, 并进行了构型优化和频率计算, 分别得到无虚频稳定的s-四嗪-(水)₂复合物、s-四嗪-(水)₃复合物和s-四嗪-(水)₄复合物6个、9个和12个. 复合物存在较强的氢键作用, 复合物结构中形成一个N…H—O氢键并终止于O…H—C氢键的氢键水链构型最稳定. 经基组重叠误差和零点振动能校正后, 最稳定的1∶2, 1∶3和1∶4(摩尔比)复合物的结合能分别是41.35, 70.9和 94.61 kJ/mol. 振动分析显示氢键的形成使复合物中水分子H—O键对称伸缩振动频率减小(红移). 研究表明N…H键越短, N…H—O键角越接近直线, 稳定化能越大, 氢键作用越强. 同时, 用含时密度泛函理论方法在TD-B3LYP/6-31＋＋G**水平计算了s-四嗪单体及其氢键复合物的第一¹(n, p*)激发态的垂直激发能.