Photoswitchable hydrazones with pyridine-based rotors and halogen substituents

Area of Science:

• Supramolecular Chemistry
• Photochemistry
• Materials Science

Background:

• Pyridine-based hydrazone photoisomerization is often hindered by pyridine rotors.
• Intramolecular hydrogen bonding influences the properties of these systems.
• Understanding photoswitching mechanisms is crucial for developing new molecular devices.

Purpose of the Study:

• To synthesize and investigate the photoswitching abilities of novel pyridine-based hydrazones with ortho-halogen substituents (2-X).
• To explore the impact of halogen atoms on photoswitching efficiency, thermodynamics, and kinetics.
• To assess the potential for molecular solar thermal energy storage.

Main Methods:

• Synthesis of a new series of pyridine-based hydrazones with 2-X substituents.
• Experimental investigation using 1H NMR and UV-Vis spectroscopy.
• Theoretical analysis employing Density Functional Theory (DFT) and Quantum Theory of Atoms in Molecules (QT-AIM) calculations.

Main Results:

• Efficient reversible photoswitching of 2-X hydrazones was achieved using UV-Vis irradiation.
• Photoisomerization yields varied, with 2-Cl-E reaching 55% efficiency.
• A new diastereomer, 2-X-E*, was identified during back-photoisomerization, supported by DFT calculations.

Conclusions:

• The introduced ortho-halogen substituents enhance the photoswitching capabilities of pyridine-based hydrazones.
• Halogen identity significantly influences switching efficiency, thermodynamics, and kinetics.
• These compounds demonstrate promise for molecular solar thermal energy storage applications.