A systematic study of thermochromic aromatic donor-acceptor materials

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Organic Electronics

Background:

• Dialkoxynaphthalene (Dan) and 1,4,5,8-naphthalene tetracarboxylic diimide (Ndi) derivatives form columnar mesophases via charge transfer.
• These mesophases exhibit tunable properties and a dark red color due to face-centered stacking.
• Some Dan-Ndi mixtures show thermochromic behavior, changing color upon crystallization.

Purpose of the Study:

• To investigate the origins of thermochromic behavior in Dan-Ndi mixtures.
• To understand how side chain modifications affect color changes during crystallization.
• To provide a structural basis for the observed thermochromism.

Main Methods:

• Systematic alteration of Dan and Ndi side chains.
• Study of 1:1 molar mixtures of modified Dan and Ndi derivatives.
• Analysis of mesophase properties and solid-state structures, including X-ray crystallography.

Main Results:

• Dan-Ndi mixtures form tunable columnar mesophases with dark red color.
• Certain mixtures undergo a dramatic color change from dark red to colorless upon crystallization without macroscopic morphological changes.
• Side chain branching significantly influences the extent of color change, with crystal structures providing a rationale.

Conclusions:

• Steric interactions introduced by side chain branching are key to controlling thermochromic behavior in Dan-Ndi systems.
• Crystal packing dictates the electronic interactions and thus the observed color changes.
• This study offers a structural understanding of thermochromism in charge-transfer materials.