Photoswitchable dendritic hosts: a dendrimer with peripheral azobenzene groups

Area of Science:

• Supramolecular Chemistry
• Photochemistry
• Materials Science

Background:

• Dendrimers are highly branched macromolecules with unique host-guest properties.
• Azobenzene units within dendrimers can undergo photoisomerization, altering their structure and properties.
• Eosin is a fluorescent dye that can interact with host molecules.

Purpose of the Study:

• To investigate the photoisomerization of azobenzene units in a dendrimer.
• To study the binding of eosin molecules to the dendrimer in different isomeric states.
• To understand the interplay between dendrimer isomerization and eosin binding capacity.

Main Methods:

• Synthesis of a fourth-generation dendrimer with azobenzene units.
• Photoisomerization of azobenzene units using UV light (365 nm).
• Spectroscopic analysis to monitor isomerization and eosin binding.
• Kinetic studies of thermal back-reactions and eosin release.

Main Results:

• Photoisomerization of the all-trans dendrimer D(32t) to a mixed cis/trans state D(4t28c) upon irradiation.
• Differential binding of eosin molecules to D(32t) (8 eosin) and D(4t28c) (6 eosin).
• Photoisomerization of the dendrimer-eosin adducts leads to eosin release and formation of photostable species.
• Eosin binding influences the isomerization kinetics of the azobenzene units.

Conclusions:

• The isomerization state of peripheral azobenzene units modulates the dendrimer's host-guest properties.
• Eosin molecules, when bound, affect the photoisomerization dynamics of the dendrimer's azobenzene units.
• This work demonstrates a photo-responsive control over dendrimer-based molecular recognition.