Competition between Photoswitching and Fluorescence in Hemiindigos and Hemithioindigos

Area of Science:

• Organic Chemistry
• Photochemistry
• Materials Science

Background:

• Intrinsically fluorescent photoswitches (IFPSs) are vital for advanced imaging like super-resolution microscopy.
• Hemiindigos (HIs) and hemithioindigos are classes of organic molecules with photoswitching potential.

Purpose of the Study:

• To investigate how substituents affect the fluorescence and photoswitching efficiency of hemiindigos and hemithioindigos.
• To explore sustainable synthesis methods for functionalized IFPSs.

Main Methods:

• One-step Knoevenagel condensation using a sustainable mechanochemical approach for synthesis.
• Characterization of synthesized derivatives in various environments.
• CC2 ab initio calculations to elucidate the photoswitching mechanism.

Main Results:

• Ortho-OH-substituted hemiindigo derivatives display high fluorescence quantum yields (ΦFL = 0.65).
• These derivatives maintain significant photoswitching efficiency (ΦZ→E = 0.29 in THF) with rapid recovery.
• Electron-donating groups, particularly the OH substituent, and intramolecular hydrogen bonds enhance IFPS properties.

Conclusions:

• The study details the photoswitching mechanism involving ππ* and nπ* excited states and conical intersections.
• Structure-property relationships were analyzed, offering guidance for the rational design of novel IFPSs.
• Mechanochemical synthesis provides a sustainable route to functionalized IFPSs.