Controlling Molecular Packing in Aqueous Metallosupramolecular Self-assembly by Ligand Geometry.

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Materials Science

Background:

• Tuning photophysical properties and self-assembly of d8 transition metal complexes is key in organic media.
• Programming noncovalent interactions in aqueous media for supramolecular assemblies remains a significant challenge.

Purpose of the Study:

• To investigate the aqueous self-assembly of amphiphilic platinum(II) complexes with different molecular geometries.
• To control self-assembly and metal-metal interactions in water through molecular design.
• To correlate molecular geometry with photophysical properties in aqueous supramolecular assemblies.

Main Methods:

• Design and synthesis of two platinum(II) complexes (1 and 2) with an oligophenyleneethynylene (OPE) scaffold, differing in linear vs. V-shaped geometry.
• Comparative analysis of their aqueous self-assembly behavior using the isodesmic mechanism.
• Investigation of molecular packing, metal-metal (Pt-Pt) contacts, and resulting photophysical properties, including metal-metal-to-ligand charge transfer (MMLCT).

Main Results:

• Both complexes (1 and 2) self-assemble via an isodesmic mechanism in water.
• Molecular geometry significantly influences packing: complex 2 shows face-to-face OPE stacking leading to short Pt-Pt contacts, while complex 1 exhibits antiparallel packing with limited Pt-Pt interaction.
• These packing differences result in distinct photophysical outcomes, specifically the presence or absence of MMLCT and varied photoluminescence.

Conclusions:

• Molecular geometry is a critical determinant for controlling supramolecular self-assembly and Pt-Pt interactions in aqueous media.
• The study demonstrates a strategy for achieving controlled photophysical properties in aqueous platinum(II) assemblies.
• Ligand design can effectively program noncovalent interactions and self-assembly pathways in water.