Resumen Se sintetizó un nuevo sistema molecular basado en 2-((2-(4-chlorofenilhidrazona)metil)quinolina. Del mismo modo, se evaluó la respuesta dinámica de este compuesto a radiación ultravioleta y formación de un enlace de hidrógeno intramolecular. Los resultados muestran que este derivado de hidrazona puede actuar como freno en solución. El sistema en mención es descrito estructural (Cristalografía de Rayos X y cálculos DFT) y espectroscópicamente (RMN, UV e IR). La interconversión de este sistema entre las configuraciones 1-E y 1-Z fue mediada por radiación UV y monitoreada a través de RMN-¹H. El estudio electroquímico mostró un comportamiento diferencial en función de su configuración, aspecto fundamental en el desarrollo de sistemas foto- y electroquímicamente modulados.

Abstract A novel molecular system based on 2-((2-(4-chlorophenylhydrazone)methyl)quinoline (1-E ) was synthesized. Interconversion of 1-E to its configurational isomer 1-Z was achieved using UV radiation (250 W Hg lamp). Such isomerization was monitored by ¹H-NMR. The results suggest that the hydrazone derivative can act as a chemical brake in solution. This molecular system was structurally (Single Crystal X-Ray diffraction and DFT calculations) and spectroscopically (NMR, UV, and IR) characterized. Electrochemical measurements showed that configurational changes induce differential redox behavior. In this regard, the reported quinoline system exhibits different dynamic absorption and electrochemical properties that are modulated by UV-light. Therefore, 1-E can be regarded as a potential photo-electrochemical switch.

Resumo Neste trabalho é apresentado um novo sistema molecular baseado na 2-((2-(4-clorofenilhidrazona)metil)quinolina, capaz de responder dinamicamente à radiação ultravioleta formando uma ligação de hidrogénio intramolecular que atua como um freio na solução. Este sistema é descrito estruturalmente (cristalografia de raios-X e DFT) e por diferentes técnicas espectroscópicas (RMN, de UV e de IV). Radiação UV foi usada para fazer a interconversão da hidrazona 1-E no seu isômero configuracional 1-Z . Este processo foi monitorado pelo RMN. As medidas eletroquímicas mostraram que as mudanças configuracionais entre os isômeros induzem a comportamentos redox diferentes, o que é uma caraterística chave no desenvolvimento de interruptores fotoelectroquímicos.

Abstract Herein we present the preparation of a bis-(hydrazone) containing a pyridine-pyrimidine- pyridine framework. This compound can be visualized as a double arm system able of coordinating two metal ions in a terpyridine-like manner. By NMR (1D and 2D) it was determined a transoid conformation and an E configuration around the two imine double bonds. Complexation with M2+ (M = Zn, Cd, and Pb) ions resulted in grid and linear type structures which were studied by cyclic and squared wave voltammetry at different temperatures. No linear correlations of the redox potentials as a function of temperature were observed. The latter is likely due to rearrangements in the structure or to spin crossover events. The present results deserve further studies on the electronic properties of these types of compounds for the development of smart materials.

Hydrazone derivatives of 2-quinolinecarboxaldehyde and 6-bromo-2-pyridinecarboxaldehyde were synthesized by sequence reactions with hydrazine derivatives. These compounds exhibited E/Z isomerization upon irradiation using a mercury lamp (250 W). The configurational changes were monitored by 1H nuclear magnetic resonance (NMR), UV-Vis and fluorescence spectroscopy. Data of concentration of the E/Z isomers versus time showed first order kinetics with constants ranging from 0.024 to 0.0799 min-1. The Z isomers were isolated by chromatographic methods and characterized by 1H NMR, UV-Vis and fluorescence spectroscopy and X-ray diffraction. The Z compounds are stable even in solution for several months. Such stability is due to a thermodynamic stabilization by the formation of an intramolecular hydrogen bond in the Z structure, which is not seen in the E configuration. Furthermore, some of the compounds were used as ligands for various metal centers (Zn2+, Co2+ and Hg2+) and their electronic properties were studied including measurements of cyclic voltammetry. The compounds studied herein allow their use as dynamic systems in dynamic combinatorial chemistry as their properties can be modulated by light, heat and the presence of metal centers. Besides, obtaining a metastable state (Z-isomer) allows the use of these compounds as photo-brakes, and therefore they can be implemented as molecular machines.