Sterically Allowed H-type Supramolecular Polymerizations.

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Organic Chemistry

Background:

• Functionalization of π-conjugated systems with bulky groups typically inhibits self-assembly by preventing cofacial stacking.
• H-type (cofacial) stacking is often undesirable as it can lead to aggregation-caused quenching and reduced material performance.

Purpose of the Study:

• To investigate the effect of increasing steric hindrance on the self-assembly and thermodynamic stability of H-type supramolecular polymers.
• To explore the role of non-covalent interactions in dictating the self-assembly behavior of functionalized dyes.

Main Methods:

• Synthesis of three boron dipyrromethene (BODIPY) dyes: meso-methyl BODIPY (1), phenyl-substituted BODIPY (2), and mesityl-substituted BODIPY (3).
• Comparative study of the self-assembly behavior of these BODIPY dyes in nonpolar media.
• Analysis of the thermodynamic stability of the resulting supramolecular structures.

Main Results:

• Increasing steric bulk on BODIPY dyes did not inhibit H-type self-assembly; instead, it enhanced the thermodynamic stability of H-type supramolecular polymers.
• Complex self-assembly pathways were observed with increased steric demand.
• The enhanced stability was attributed to favorable intermolecular C-H⋅⋅⋅F-B interactions between orthogonally arranged aromatic substituents, which compensated for steric repulsion.

Conclusions:

• Steric effects can unexpectedly promote thermodynamic stability in H-type supramolecular polymers.
• Balancing competing non-covalent interactions, such as steric repulsion and specific attractive forces (C-H⋅⋅⋅F-B), is crucial for controlling self-assembly.
• This work challenges the conventional understanding of steric hindrance in π-conjugated system self-assembly.