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E. Zerobin, W. Steiger, M. Markovic, S. Baudis, A. Ovsianikov, R. Liska:
"Molecular Design Towards Novel Photo-Initiators with Increased Two-Photon Absorption Cross Section";
Vortrag: VSS 2018 - Vienna Young Scientists Symposium, Wien; 07.06.2018 - 08.06.2018; in: "VSS 2018", Book-of-Abstracts.com, (2018), ISBN: 978-3-9504017-8-3; S. 106 - 107.

Photopolymerization has become a valuable technique within additive manufacturing technologies (AMTs) to locally crosslink photosensitive polymers with high temporal and spatial control.[1] In order to initiate radical photopolymerization a variety of photo-initiators (PIs) are available. Two-photon polymerization (2PP) has been recently employed within the biomedical sector, since photopolymers can be crosslinked under relatively mild conditions.[2] Two-photon absorption (2PA) is a non-linear optical process, only occurring at the focal point of laser beams, where intensities are high enough for two-photon initiators (2PIs) to absorb the energy of two photons simultaneously. In contrast to one-photon absorption, where molecules are excited to an electronic state, which corresponds to the energy of one photon, 2PA is a process with rather low probability and requires extremely high laser peak powers. Due to the high transparency of biological tissues towards the pulsed infrared laser it is possible to scan the laser through a liquid formulation, enabling 3D printing in the presence of living tissue. For this process, molecules with large 2PA cross sections are needed, to ensure efficient radical polymerization. Planar and multi-polar molecules with electron donating and -withdrawing groups, as well as large delocalized π-electron systems have been known to show large 2PA cross sections. These structural properties of 2PIs have been studied to enhance polarization of molecules and their absorption properties, necessary for 2PP.[3] Continuous development of 2PIs is crucial to ensure efficient photopolymerization of new systems. There are several concepts in order to increase 2PI efficiency, such as reducing the chance of unwanted processes like back electron-transfer (BET). BET simply reverses reaction kinetics of the initiation reaction, thus decreasing 2PI activity. By the introduction of efficiently and irreversibly cleavable functional groups, such as oxime ester functionalities, BET can be minimized.

Photopolymerization, Novel Photo-Initiators