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4-OH coumarin based rotary switches: Tautomeric state and effect of the stator
Dyes and Pigments ( IF 4.5 ) Pub Date : 2020-09-15 , DOI: 10.1016/j.dyepig.2020.108861
Dancho Yordanov , Vera Deneva , Anton Georgiev , Nikolay Vassilev , Martin Vala , Ivaylo Zhivkov , Liudmil Antonov

Two new 4-OH coumarin based rotary switches, containing fixed carbonyl groups in the rotor, have been synthesized and their properties have been studied by combined use of DFT calculations and molecular spectroscopy (UV–Vis absorbance and emission, NMR). It was found that the structure of the stator (naphthyl in 2 or quinolyl moiety in 3) and solvents polarity do not influence their azo-hydrazone tautomerism. Both compounds exist as keto (hydrazone) tautomers. The NMR data indicate a mixture of E (major) and Z (minor) keto form isomers in solution. The results are in very good agreement with ground state DFT calculations. The keto tautomers exhibit different emission behavior depending on the structure of the stators. Comparing to 2, more intensive emission and higher lifetime was observed in 3, where the formation of intramolecular hydrogen bonding of the hydrazone NH with the N atom of quinoline restricts the rotation of the stator. According to the spectral data and the TDDFT analysis the observed emission originates from the excitation of the keto tautomers and does not include excited state proton transfer. It was shown that the protonation is a suitable stimulus for E/Z switching in 2, where a possible mechanism is sketched. In the case of 3, the addition of acid leads to the protonation of the quinolyl nitrogen atom, which slightly affects the E/Z isomerization ratio.



中文翻译:

基于4-OH香豆素的旋转开关:互变异构状态和定子的作用

已经合成了两个新的基于4-OH香豆素的旋转开关,它们在转子中包含固定的羰基,并且通过结合使用DFT计算和分子光谱学(UV-Vis吸收和发射,NMR)研究了它们的性能。已经发现,定子的结构(2为萘基或3为喹啉基)和溶剂极性不影响其偶氮hydr互变异构现象。两种化合物都以(hydr)互变异构体的形式存在。NMR数据表明溶液中有E(主要)和Z(次要)酮的异构体的混合物。结果与基态DFT计算非常吻合。该互变异构体根据定子的结构表现出不同的发射行为。与2相比,在3中观察到更强的发射和更长的寿命,其中theNH与喹啉的N原子的分子内氢键的形成限制了定子的旋转。根据光谱数据和TDDFT分析,观察到的发射源于互变异构体的激发,不包括激发态质子转移。结果表明,质子化是2中E / Z切换的合适刺激,其中画出了可能的机理。在3的情况下,添加酸会导致喹啉基氮原子的质子化,这会稍微影响E / Z异构化率。

更新日期:2020-09-29
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