A General Strategy To Access Fluorogenic Heptamethine Cyanines through Polymethine Reactivity.

Area of Science:

• Organic Chemistry
• Materials Science
• Biomedical Imaging

Background:

• Fluorogenic heptamethine cyanine dyes are valuable tools for biomedical imaging.
• Existing strategies for developing these dyes are limited.
• There is a need for novel approaches to synthesize and control cyanine dye properties.

Purpose of the Study:

• To report a novel polymethine reactivity-based approach for synthesizing fluorogenic heptamethine cyanine dyes.
• To investigate the formation of cyclized structures and their impact on π-conjugation.
• To explore the solvent-dependent fluorescence behavior of the novel dyes.

Main Methods:

• A polymethine reactivity-based strategy was employed.
• Intramolecular nucleophilic attack of a meso-carboxylate at the γ-position was utilized.
• The effect of indolenine substitution on cyclization equilibrium was examined.

Main Results:

• A new class of cyclizing Cy7 (c-Cy7) dyes was successfully synthesized.
• These dyes exhibit a solvent-dependent equilibrium between open (fluorescent) and closed (nonfluorescent) forms.
• The equilibrium shifts towards the open, fluorescent form in polar solvents and the closed, nonfluorescent form in nonpolar solvents.
• Indolenine substitution was found to modulate the cyclization equilibrium, offering a way to tune dye properties.

Conclusions:

• The reported polymethine reactivity-based approach provides a new strategy for developing fluorogenic heptamethine cyanine dyes.
• The resulting cyclizing Cy7 dyes offer tunable fluorescence properties based on solvent polarity.
• This work expands the toolkit for designing advanced cyanine dyes for biomedical imaging applications.