Solid-State Photoswitching of Hydrazones Based on Excited-State Intramolecular Proton Transfer

Area of Science:

• Materials Science
• Photochemistry
• Organic Chemistry

Background:

• Photochromic systems offer reversible control over material properties.
• Solid-state photochromism is challenging due to confinement effects.
• Triaryl-hydrazones are bistable photoswitches effective in solution.

Purpose of the Study:

• To investigate solid-state photochromism in novel triaryl-hydrazones.
• To explore the mechanism behind unexpected spectral shifts.
• To assess the potential of these systems in optics and optoelectronics.

Main Methods:

• Synthesis of new triaryl-hydrazones with perfluorinated hydrazine phenyl rings (PHZs).
• Spectroscopic analysis (UV-Vis, NMR, EPR) and X-ray diffraction.
• (Time-dependent) Density Functional Theory (TD-DFT) calculations.
• Confocal Raman microscopy for surface analysis.

Main Results:

• The Z-isomers of PHZs exhibit efficient solid-state photochromism.
• An unexpected light-induced red-shift in absorption maximum was observed.
• A mechanism involving excited-state intramolecular proton transfer explains the red-shift.
• Photochromism was confirmed as a superficial phenomenon.

Conclusions:

• Perfluorinated triaryl-hydrazones demonstrate significant solid-state photochromic behavior.
• The observed red-shift is attributed to a metastable proton transfer structure.
• PHZs show potential for applications in optics and optoelectronics due to their performance in thin films and with visible light.