Catalyst Halogenation Enables Rapid and Efficient Polymerizations with Visible to Far-Red Light

Area of Science:

• Polymer Chemistry
• Photocatalysis
• Materials Science

Background:

• Current photopolymerization methods face limitations in reaction speed, light intensity, and catalyst requirements.
• Developing efficient photocatalysts is crucial for advancing bio- and composite-printing technologies.

Purpose of the Study:

• To synthesize and characterize novel boron dipyrromethene (BODIPY) derivatives for efficient visible-light-driven photopolymerization.
• To elucidate the structure-property relationships governing photocatalysis in polymerization.
• To achieve rapid polymerization rates with reduced light intensity and catalyst loading.

Main Methods:

• Synthesis and characterization of methine- and aza-bridged BODIPY derivatives.
• Quantitative polymerization rate analysis using real-time infrared spectroscopy.
• Mechanistic studies involving emission quenching, electronic structure calculations, and ultrafast transient absorption spectroscopy.

Main Results:

• Halogenation of BODIPY scaffolds was identified as a key strategy to enhance polymerization rates.
• Efficient intersystem crossing to the triplet state upon halogenation was confirmed as the primary mechanism for accelerated polymerization.
• Achieved unprecedented polymerization rates with very low light intensities (<1 mW/cm²) and catalyst loadings (<50 μM), completing reactions in under 60 seconds.
• Demonstrated successful 3D printing of complex structures using halogenated BODIPY catalysts and visible light.

Conclusions:

• Halogenated BODIPY derivatives are highly efficient photoredox catalysts for rapid polymerization.
• The enhanced performance is attributed to improved intersystem crossing facilitated by halogenation.
• These catalysts offer significant advantages for additive manufacturing and emerging printing technologies.