Rotaxane Formation Increases Squaraine Fluorescence Brightness beyond 900 nm by 25-fold

Area of Science:

• Organic chemistry
• Photophysics
• Supramolecular chemistry

Background:

• Squaraine dyes exhibit strong absorption but suffer from low fluorescence quantum yields due to structural flexibility.
• Developing brighter and more stable fluorescent probes is crucial for advanced imaging and sensing applications.

Purpose of the Study:

• To enhance the fluorescence brightness and photophysical properties of a squaraine dye.
• To investigate the effect of structural rigidification on dye performance.

Main Methods:

• Synthesized a squaraine dye featuring benzo[cd]indoles.
• Encapsulated the dye within a rotaxane structure to restrict its flexibility.
• Measured absorption and emission spectra, and fluorescence quantum yield.

Main Results:

• The rigidified squaraine dye showed a 25-fold increase in fluorescence brightness.
• The rotaxane-based dye exhibited SWIR emission peaking at 915 nm and extending beyond 1100 nm.
• Excitation of anthrylene sidewalls resulted in a large pseudo-Stokes shift of 540 nm.

Conclusions:

• Rotaxane encapsulation effectively rigidifies squaraine dyes, significantly boosting fluorescence brightness.
• The enhanced dye is suitable for SWIR imaging and sensing applications.
• The observed large pseudo-Stokes shift offers potential for novel optical applications.