Abstract
Two-photon induced polymerization (2PP) based 3D printing is a powerful microfabrication tool. Specialized two-photon initiators (2PIs) are critical components of the employed photosensitive polymerizable formulations. This work investigates the cooperative enhancement of two-photon absorption cross sections (σ2PA) in a series of 1,3,5-triazine-derivatives bearing 1-3 aminostyryl-donor arms, creating dipolar, quadrupolar and octupolar push-pull systems. The multipolar 2PIs were successfully prepared and characterized, σ2PA were determined using z-scan at 800 nm as well as spectrally resolved two-photon excited fluorescence measurements, and the results were compared to high-level ab initio computations. Modern tunable femtosecond lasers allow 2PP-processing at optimum wavelengths tailored to the absorption behavior of the 2PI. 2PP structuring tests revealed that while performance at 800 nm is similar, at their respective σ2PA-maxima the octupolar triazine-derivative outperforms a well-established ketone-based quadrupolar reference 2PI, with significantly lower fabrication threshold at exceedingly high writing speeds up to 200 mm/s and a broader window for ideal processing parameters.
Highlights
Two-photon induced polymerization (2PP) based 3D printing is a powerful microfabrication tool
The molecules BTrz, 2BTrz, and 3BTrz (Fig. 1) based on the 1,3,5-triazine acceptor form a series of di, quadru, and octupolar molecules, respectively, that were synthesized to investigate their suitability as 2PIs
The three increasingly branched aminostyryl triazine derivatives were obtained analogous to literature[14] by subsequently reacting the three methyl groups of Trz with 4-(dibutylamino)benzaldehyde (DBA) in a Knoevenagel-type condensation under alkaline catalysis using potassium hydroxide in methanol (Fig. 2)
Summary
Two-photon induced polymerization (2PP) based 3D printing is a powerful microfabrication tool. Commercial PIs used in UV-light induced one-photon polymerization of classical coatings can be employed to generate microstructures via 2PP7,8 They suffer from limitations such as very narrow windows for ideal processing parameters and exceedingly slow achievable writing speeds due to their inefficient two-photon absorption (2PA), expressed as a low 2PA cross section (σ2PA)[9]. Previous studies show that 1,3,5-triazine derivatives bearing 1,4-phenylenevinylene arms with terminal dialkylamino-groups (aminostyryl-1,3,5-triazines) exhibit relatively high 2PA that strongly increases in a non-linear fashion with the number of branches[11,14,15] These factors make branched systems containing a triazine core element promising 2PI-candidates, so that in this work a series of multipolar aminostyryl-1,3,5-triazines (Fig. 1) was prepared to investigate their relevant photophysical properties and their efficiency regarding the application as 2PIs
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