Developing strong NIR absorption materials through linear planar π-conjugated cyclopalladated complex dimers

Area of Science:

• Coordination Chemistry
• Materials Science
• Photophysics

Background:

• Near-infrared absorbing metal complexes (NIRMCs) typically rely on complex π-expanded macrocyclic structures.
• Existing macrocyclic ligands for NIRMCs present synthetic challenges and limited structural diversity.

Purpose of the Study:

• To report a new class of NIRMCs utilizing linear, large, planar π-conjugated cyclopalladated dimers.
• To establish a facile synthetic route for these novel NIRMCs.
• To investigate their near-infrared absorption and emission properties.

Main Methods:

• Synthesis of linear large planar π-conjugated cyclopalladated dimers via base-induced dimerization of monomers.
• Spectroscopic analysis to determine NIR absorption and fluorescence emission characteristics.

Main Results:

• The synthesized cyclopalladated dimers exhibit intense NIR absorption (ε770 nm = 2.5 × 105 cm-1 M-1).
• These complexes display fluorescence emission peaks around 910 nm.
• Quinoid thiophene methine (QTM) and the cyclopalladated structure are identified as key contributors to strong NIR absorption.

Conclusions:

• A facile method for preparing NIRMCs based on cyclopalladated dimers has been developed, bypassing complex macrocyclic synthesis.
• The findings provide a new structural paradigm for designing and synthesizing NIR absorption metal complexes.
• These novel complexes hold potential for applications requiring strong NIR absorption and emission.