Near Infrared Dyes Based on Diradicaloids: Molecular Design, Photophysical Properties and Bioapplications.

Area of Science:

• Materials Science
• Biotechnology
• Organic Chemistry
• Photophysics

Background:

• Organic near-infrared (NIR) dyes are crucial for materials science and biotechnology.
• Conventional NIR dye design faces challenges in achieving long-wavelength optical properties, especially in the NIR-II region (1000-1700 nm).
• Existing methods often struggle with bandgap modulation and extending optical features beyond 800 nm.

Purpose of the Study:

• To review the molecular design principles, photophysical properties, and biomedical applications of diradicaloid-based NIR dyes.
• To highlight diradicaloids as a promising alternative for developing NIR dyes with tunable optical properties.
• To provide a framework for designing next-generation diradicaloid NIR dyes for high-performance bioapplications.

Main Methods:

• Systematic review of diradicaloid molecular design principles.
• Analysis of photophysical properties, including HOMO-LUMO admixing and symmetry-breaking charge transfer (SBCT).
• Exploration of structural modifications (conjugation extension, substituent engineering, heteroatom incorporation) to tune diradical character and NIR photoresponse.

Main Results:

• Diradicaloid design leverages open-shell electronic nature for exceptionally narrow bandgaps.
• This approach enables strong absorption/emission in the long-wavelength NIR region.
• Structural modifications effectively tune the diradical character index (y₀), impacting stability and NIR photoresponse.

Conclusions:

• Diradicaloid-based NIR dyes present a viable strategy to overcome limitations of conventional NIR dye design.
• These dyes show significant potential for advanced biomedical applications due to their tunable NIR optical properties.
• The review provides actionable insights for developing novel diradicaloid NIR dyes.