Designing small organic molecular NIR-II fluorophores by ring strain modulation.

Area of Science:

• Organic Chemistry
• Materials Science
• Biomedical Imaging

Background:

• Developing organic fluorophores for the second near-infrared window (NIR-II, 1000-1700 nm) is crucial for advanced in vivo bioimaging and biosensing.
• Existing fluorophores often require optimization for superior photophysical properties and in vivo applicability.

Purpose of the Study:

• To explore a novel strategy for modulating the optical properties of xanthene-based fluorophores.
• To investigate the impact of ring strain, controlled by ring size, on fluorophore characteristics.
• To develop responsive fluorophores for biosensing applications.

Main Methods:

• Synthesized a series of xanthene-based fluorophores with systematically varied ring sizes.
• Investigated the relationship between ring size, ring strain, molecular rigidity, and planarity.
• Analyzed the photophysical properties (absorption, emission, quantum yield) of the synthesized compounds.
• Assessed the responsiveness of the fluorophores by measuring their pK_cycl values influenced by spirocyclization.

Main Results:

• Fine-tuning the ring size of xanthene derivatives effectively modulated their ring strain.
• Increased ring strain led to enhanced rigidity and planarity of the conjugated system, significantly impacting optical properties.
• Spirocyclization due to ring strain influenced the pK_cycl values, conferring responsiveness to the fluorophores.
• The developed fluorophores demonstrated potential for applications in the NIR-II window.

Conclusions:

• Manipulating ring strain through controlled ring size is a viable strategy to tune the optical properties of xanthene-based fluorophores.
• This approach enables the development of novel organic fluorophores with desirable characteristics for in vivo bioimaging and biosensing in the NIR-II region.
• The study provides a foundation for designing next-generation responsive fluorescent probes.