Novel Highly Potential Initiators for the Two-Photon-Induced Photopolymerization Process
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Novel Highly Potential Initiators for the Two-Photon-Induced Photopolymerization Process Niklas Pucher,1 Valentin Satzinger,2 Arnulf Rosspeintner,3 Georg Gescheidt,3 Volker Schmidt,2 Jürgen Stampfl,4 and Robert Liska1 1
Institute of Applied Synthetic Chemistry (Division: Macromolecular Chemistry), Vienna University of Technology, Vienna, Vienna, Austria. 2 Institute of Nanostructured Materials and Photonics, Joanneum Research, Weiz, Styria, Austria. 3 Institute of Physical and Theoretical Chemistry, Graz University of Technology, Graz, Styria, Austria. 4 Institute of Materials Science and Technology, Vienna University of Technology, Vienna, Vienna, Austria. ABSTRACT The development of new optimized photoinitiators for the two-photon induced photopolymerization (TPIP) is essential in order to obtain high resolutions in this solid freeform fabrication process. Herein, we present the syntheses and characterizations of a series of efficient photoinitiators, comprising of a cross-conjugated D-π-A-π-D system. The different donor- and acceptor functionalities of the investigated photoinitiators as well as the synthesis of targeted derivatives containing double and triple bonds in the conjugated backbone allowed the evaluation of structure-activity relationships. The basic photophysical properties as well as the activity and ideal processing window under TPIP conditions were investigated for each initiator and compared with typical commercially available one-photon initiator and with two highly potential initiators well known from literature. These tests figured out that the new chromophores are highly potential even at concentrations down to 0.05 wt%. INTRODUCTION In the last decade, two-photon induced photopolymerization (TPIP) [1-3] has attracted much attention of researchers and has been intensely studied for various future applications requiring three dimensional (3D) structures with resolutions in the (sub)micrometer range, such as different mechanical, electronic and optical micro devices,[1] polymer-based optical waveguides on integrated circuit boards,[4,5] and the like. The photoinitiator (PI) plays a key role in order to obtain an efficient polymerization and therefore high quality structures. Up to now, a full understanding of the relationship of the molecular structure and the two-photon properties has still remained a big challenge for researchers. A high two-photon absorption (TPA cross-section) combined with a high quantum yield of initiation just like for conventional one-photon initiators is essential. To obtain these, a planar π system with a long conjugation length and with different functional donor (D) and/or acceptor (A) groups are important structural parameters.[3] Herein, we present the syntheses and characterizations of a series of efficient PIs, comprising of a same cross-conjugated D-π-A-π-D system. In order to study structure-activity relationships, variation of the functional donor (hydrogen-, methoxy-, thiomethyl-, dimethylamino-, diphenylamino-, and dibutylamino-groups)
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