Two-Dimensional Supramolecular Polymorphism in Cyanine H- and J-Aggregates.

Area of Science:

• Supramolecular chemistry
• Materials science
• Photonic materials

Background:

• Cyanine dyes are versatile chromophores with applications in various optical technologies.
• Supramolecular polymers offer tunable properties through self-assembly.
• Controlling the assembly of dyes into specific architectures, like 2D aggregates, is crucial for advanced materials.

Purpose of the Study:

• To design and synthesize a novel cyanine dye capable of forming distinct 2D supramolecular polymorphs.
• To investigate the self-assembly pathways and polymorph transitions of the cyanine dye.
• To explore the potential of these polymorphs as new 2D photoactive materials.

Main Methods:

• Synthesis of a new cyanine dye with rod-like groups.
• Investigation of supramolecular assembly in methylcyclohexane.
• Utilizing thermal transformation, cooling, and sonication to induce polymorph transitions.
• Characterization of H-type (Agg-H2) and J-type (Agg-J) aggregates from a particle-like precursor (Agg-H1).

Main Results:

• Successful design of a cyanine dye that forms two distinct 2D supramolecular polymorphs: Agg-H2 (H-type) and Agg-J (J-type).
• Demonstration that these polymorphs arise from the thermal transformation of a precursor (Agg-H1), not polymerization.
• Discovery of a thermoreversible transition for Agg-H2 formation and a hidden pathway involving sonication and cooling for Agg-J.
• Isolation of both H- and J-type cyanine polymorphs in solid-state, yielding new 2D photoactive materials.

Conclusions:

• This work presents the first report of H- and J-type cyanine polymorphs formed via non-polymerization pathways.
• New strategies for designing 2D supramolecular polymers using calamitic residues have been unveiled.
• Understanding pathway complexity and polymorph transitions is vital for developing novel photonic systems.