Twisting Rhodamine─Design of Bright Dyes for Circularly Polarized Fluorescence.

Area of Science:

• Organic Chemistry
• Materials Science
• Photophysics

Background:

• Chiral molecules with conjugated π-systems, such as helicenes, are promising for circularly polarized luminescence (CPL).
• Rhodamine dyes are highly fluorescent and widely used in biological imaging due to their brightness and stability.
• Combining these functionalities could lead to advanced CPL dyes for specialized applications.

Purpose of the Study:

• To synthesize and characterize novel chiral helicene-based dyes incorporating a rhodamine chromophore.
• To investigate the impact of electron-donating group substitution on the photophysical and chiroptical properties.
• To achieve enhanced CPL emission and explore potential bioapplications.

Main Methods:

• Development of an original synthetic pathway for cationic [4]helicenes.
• Structural modification of a chromenoxanthenium [4]helicene scaffold with varying electron-donating groups.
• Spectroscopic analysis to determine absorption, fluorescence, and CPL properties, including quantum yields and dissymmetry factors.

Main Results:

• Successfully synthesized three new cationic [4]helicenes with a rhodamine core.
• Demonstrated that substitution patterns influence lowest-energy transitions, improving fluorescence and chiroptical properties.
• Achieved CPL brightness up to 4 times higher than previously reported cationic [4]helicenes.
• The final helicene exhibited high absorption, outstanding quantum yields, and an increased dissymmetry factor.

Conclusions:

• The integration of a rhodamine chromophore into a stable helicene framework yields highly efficient CPL dyes.
• Strategic substitution allows for tuning of photophysical properties, leading to superior CPL performance.
• The introduction of an N-acyl handle provides a platform for future functionalization and bio-applications.