Harvesting light energy by iridium(III) complexes on a clay surface

Area of Science:

• Materials Chemistry
• Photochemistry
• Supramolecular Chemistry

Background:

• Iridium(III) complexes are crucial in photochemistry and materials science.
• Synthetic saponites offer a versatile platform for adsorbing and organizing molecular species.
• Understanding energy transfer mechanisms is key to developing advanced light-harvesting systems.

Purpose of the Study:

• To investigate energy transfer (ET) between iridium(III) donor and acceptor complexes co-adsorbed on synthetic saponite.
• To explore the role of alkyl chain length in iridium(III) complexes on ET efficiency and enantioselectivity.
• To elucidate the mechanism of light energy harvesting facilitated by these supramolecular assemblies.

Main Methods:

• Co-adsorption of iridium(III) complexes ([Ir(dfppy)2(Cn-bpy)](+) and [Ir(piq)2(Cn-bpy)](+)) onto colloidally dispersed synthetic saponite.
• Spectroscopic analysis of emission spectra to determine energy transfer efficiency (η(ET)) at various donor-to-acceptor ratios (D/A).
• Application of the Förster-type energy transfer model to quantify ET processes.

Main Results:

• High energy transfer efficiency (η(ET) up to 0.5) was observed for complexes with short alkyl chains (C1-bpy) at a D/A ratio of ~20.
• Evidence of light energy harvesting, where multiple donor molecules transfer energy to a single acceptor molecule.
• Enantioselectivity was detected for C1-bpy, suggesting the formation of contact pairs between donor and acceptor molecules.
• Low energy transfer efficiency and lack of enantioselectivity were found for complexes with long alkyl chains (C12-bpy, C19-bpy) due to inhibited molecular contact.

Conclusions:

• Short alkyl chains in iridium(III) bipyridine ligands are crucial for efficient Förster-type energy transfer and enantioselectivity when co-adsorbed on saponite.
• Synthetic saponite effectively facilitates light energy harvesting through organized co-adsorption of iridium(III) complexes.
• The length of alkyl chains on bipyridine ligands significantly impacts the proximity and interaction between donor and acceptor iridium(III) complexes, thereby controlling energy transfer dynamics.