Engineering Azobenzene Derivatives to Control the Photoisomerization Process.

Area of Science:

• Photochemistry
• Molecular design
• Spectroscopy

Background:

• Azobenzene derivatives are photoactive molecules with potential applications in photoswitches.
• Understanding the relationship between molecular structure and photoisomerization is crucial for designing efficient photoswitches.

Purpose of the Study:

• To investigate how structural features, specifically intramolecular interactions and tautomerism, influence the photoexcited state behavior and trans/cis photoisomerization of azobenzene derivatives.
• To provide guidelines for designing azobenzene-based photoswitches with tunable properties.

Main Methods:

• High-resolution transient absorption experiments in the visible-near-infrared (vis-NIR) region.
• Quantum chemistry calculations, including time-dependent density functional theory (TDDFT) and restricted active space second-order perturbation theory (RASPT2).
• Study of three poly-substituted push-pull azobenzenes and a commercial red dye (Sudan Red G) with varying intramolecular interactions and keto-enol tautomerism.

Main Results:

• Intramolecular H-bonds stabilize the trans isomer and increase the energy barrier for photoisomerization, effectively acting as a "molecular lock" in Disperse Blue dyes.
• Keto-enol tautomerism involving the azo group alters the excited state nature and favors productive torsional motion over nonproductive bending pathways, promoting photoisomerization in Sudan Red G.
• The strength of intramolecular interactions directly correlates with the degree of photoisomerization inhibition.

Conclusions:

• Molecular structural modifications, such as intramolecular H-bonds and keto-enol tautomerism, can precisely control the photoisomerization efficiency of azobenzene derivatives.
• These findings offer valuable insights for the rational design of novel azobenzene-based photoswitches with tailored excited-state dynamics and photoresponsive behavior.