Metal-Free Singlet Oxygen Generation via Excited-State Intramolecular Proton-Transfer-Driven Intersystem Crossing in...

Area of Science:

• Photocatalysis
• Materials Science
• Organic Chemistry

Background:

• Singlet oxygen (¹O₂) is crucial for photodynamic therapy and organic synthesis.
• Conventional methods use metal sensitizers, posing biocompatibility and scalability issues.
• Metal-free approaches are needed for sustainable and efficient ¹O₂ generation.

Purpose of the Study:

• To develop a metal-free strategy for enhanced singlet oxygen (¹O₂) production.
• To investigate the role of excited-state intramolecular-proton-transfer (ESIPT) in ¹O₂ generation.
• To compare the performance of 1D polymers and 2D covalent organic frameworks (COFs) in ESIPT-mediated ¹O₂ synthesis.

Main Methods:

• Synthesis and characterization of 1D polymers and 2D COFs utilizing ESIPT.
• Time-resolved spectroscopic studies to monitor ESIPT and intersystem crossing (ISC) dynamics.
• Thermodynamic analysis and frontier molecular orbital calculations to elucidate ISC mechanisms.

Main Results:

• Two-dimensional COFs exhibit stabilized ESIPT transitions, leading to a persistent metastable state.
• This stabilized state in 2D COFs facilitates enhanced intersystem crossing (ISC) compared to 1D polymers.
• ESIPT in 2D COFs triggers ISC, significantly boosting singlet oxygen (¹O₂) generation.

Conclusions:

• Two-dimensional COF-based ESIPT transformations offer a superior metal-free pathway for efficient ¹O₂ generation.
• The stabilized tautomeric transition in 2D COFs is key to enhancing ISC efficiency.
• This work expands the application of ESIPT in photocatalysis, particularly for boosting ¹O₂ production.