Antonov Liudmil, Deneva Vera, Simeonov Svilen, Kurteva Vanya, Crochet Aurelien, Fromm Katharina M, Shivachev Boris, Nikolova Rositsa, Savarese Marika, Adamo Carlo
Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev str., bl. 9, 1113 Sofia (Bulgaria).
Chemphyschem. 2015 Feb 23;16(3):649-57. doi: 10.1002/cphc.201402691. Epub 2014 Dec 8.
A series of new tautomeric azonaphthols are synthesized and the possibilities for molecular switching are investigated using molecular spectroscopy, X-ray analysis and density functional theory quantum chemical calculations. Two opposite effects that influence switching are studied: attaching a piperidine sidearm, and adding substituents to the phenyl ring. On the one hand, the attached piperidine moiety stabilizes the enol form leading to a controlled shift of the equilibrium upon protonation. On the other hand, the relative stability of the azonaphthol tautomers strongly depends on the effects of the substituents on the phenyl ring: electron donors tend to stabilize the enol tautomer, whereas electron acceptors lead to stabilization of the keto form. However, these effects do not shift fully the equilibrium towards either of the tautomers. Nevertheless, the effect of the substituents can be an additional tool to affect the switching between "on" and "off" states. Electron-withdrawing substituents stabilize the keto form and impede switching to the off state, whereas electron donors stabilize the enol form. The effect of the piperidine unit is dominant overall, and with strongly electron-withdrawing substituents at the phenyl ring, the enol form exists as a zwitterion.
合成了一系列新的互变异构氮萘酚，并使用分子光谱、X射线分析和密度泛函理论量子化学计算研究了分子开关的可能性。研究了影响开关的两种相反效应：连接哌啶侧链和在苯环上添加取代基。一方面，连接的哌啶部分使烯醇形式稳定，导致质子化时平衡发生可控移动。另一方面，氮萘酚互变异构体的相对稳定性强烈取决于苯环上取代基的效应：供电子体倾向于使烯醇互变异构体稳定，而电子受体导致酮式稳定。然而，这些效应并没有使平衡完全偏向任何一种互变异构体。尽管如此，取代基的效应可以作为影响“开”和“关”状态之间切换的额外工具。吸电子取代基使酮式稳定并阻碍切换到关闭状态，而供电子体使烯醇形式稳定。哌啶单元的效应总体上占主导，并且在苯环上有强吸电子取代基时，烯醇形式以两性离子形式存在。
