Two- and three-photon processes during photopolymerization in 3D laser printing

Area of Science:

• Photochemistry
• Polymer Science
• Nanotechnology

Background:

• Photoinitiators are crucial for 3D laser nanoprinting efficiency and resolution.
• 7-diethylamino-3-thenoylcoumarin (DETC) is a widely used photoinitiator, but its radical formation mechanisms are not fully understood.
• Understanding these mechanisms is key to optimizing 3D laser nanoprinting processes.

Purpose of the Study:

• To investigate the molecular mechanisms of free radical polymerization (FRP) initiation by DETC in 3D laser nanoprinting.
• To elucidate the pathways of radical generation upon single- and multi-photon excitation of DETC.
• To explain the role of co-initiators in DETC-mediated FRP.

Main Methods:

• Experimental investigation of DETC photophysics and photochemistry.
• Quantum mechanical calculations to model multiphoton activation processes.
• Analysis of radical formation pathways under different excitation conditions and in the presence/absence of co-initiators.

Main Results:

• DETC initiates FRP via three-photon excitation through highly excited triplet states, involving hydrogen-atom transfer from pentaerythritol triacrylate (PETA) monomers.
• Radical formation is less spontaneous for DETC itself compared to its active radicals.
• In the presence of onium salt co-initiators, photoinitiation proceeds via intermolecular electron transfer after photosensitization to the lowest triplet excited state.

Conclusions:

• This study provides the first detailed description of FRP initiation pathways by DETC in 3D laser nanoprinting.
• The findings explain the distinct radical formation mechanisms based on excitation conditions and co-initiator presence.
• This research enables the rational design of novel photoinitiators to enhance the speed and sensitivity of 3D laser nanoprinting.