Multi Photon Initiators

Generally, in Multi-Photon Lithography [1], also frequently called Two Photon induced Polymerization (TPIP) a resin, that contains mainly a multifunctional monomer (typically acrylate-based) and a photoinitiator, is cured inside the focal point of a fs pulsed near infrared laser beam to produce a desired 3D shape with a resolution down to 100 nm. As usual single photon initiators have only limited two photon absorption properties specialized molecules have to be desinged containing a long planar pi-system and strong electron donor and or acceptor groups are required.

Initiators known from literature have the disadvantages of deactivation of the excited singlet state by fluoreszenz and cis-trans isomerization of the double bonds.

Therefore our group has synthesized the triple bond containing 1,5-bis(4-(dibutylamino)phenyl)penta-1,4-diyn-3-one (B3K) that have a high (of 238 GM in 800 nm) two photon absorption cross-section. Subsequently, based on the molecular structure of B3K containing triple bonds and cross-conjugated D-π-A-π-D lead structures, we continue to investigated several aromatic ketone-based (benzophenone, fluorenone and anthraquinone) TPA PIs. All aromatic ketone-based TPA PIs exhibit large two-photon cross sections ranging from 250 GM to 440 GM. The 2, 7-substituted fluorenone-based PI B3FL, with strong TPA and diminishing fluorescence, exhibits broader processing window in TPP structuring tests than that of B3K. While high reactivity could be obtained in TPIP with PI concentrations as low as 0.1% wt, B3FL is surprisingly stable under one photon condition and nearly no photoinitiation activity was found in classical photo DSC experiments [2-6]. Especially the application in tissue engineering is of high interest as tissue is transparent to the applied laser wavelngeth. Therefore biocompatible initiators have been developed [7].

[1] J. Stampfl, R. Liska, A. Ovsianikov: "Multiphoton Lithography: Techniques, Materials and Applications" Wiley‐VCH, (2016)

[2] C. Heller, N.U Pucher, B. Seidl, K. Kalinyaprak-Icten, G. Ullrich, L. Kuna, V. Satzinger, V. Schmidt, H. Lichtenegger, J. Stampfl, R. Liska: "One- and two-photon activity of cross-conjugated photoinitiators with bathochromic shift"; Journal of Polymer Science Part A: Polymer Chemistry, 45 (2007), S. 3280 - 3291.

[3] N.U Pucher, A. Rosspeintner, V. Satzinger, V. Schmidt, G. Gescheidt, J. Stampfl, R. Liska: "Structure-Activity Relationship in D-π-A-π-D-Based Photoinitiators for the Two-Photon-Induced Photopolymerization Process"; Macromolecules, 42 (2009), S. 6519 - 6528.

[4] Z. Li, M. Siklos, N.U Pucher, K. Cicha, A. Ajami, W. Husinsky, A. Rosspeintner, E. Vauthey, G. Gscheidt, J. Stampfl, R. Liska: "Synthesis and Structure-Activity Relationship of Several Aromatic Ketone-Based Two-Photon Initiators"; Journal of Polymer Science Part A: Polymer Chemistry, 49 (2011), S. 3688 - 3699.

[5] Z. Li, N.U Pucher, K. Cicha, J. Torgersen, S. Ligon, A. Ajami, W. Husinsky, A. Rosspeintner, E. Vauthey, S. Naumov, T. Scherzer, J. Stampfl, R. Liska: "Straightforward Synthesis and Structure-Activity Relationship of Highly Efficient Initiators for Two-Photon Polymerization"; Macromolecules, 46 (2013), 2; S. 352 - 361.

[6] M. Tromayer, P. Gruber, A. Rosspeintner, A. Ajami, W. Husinsky, F. Plasser, L. Gonzalez, E. Vauthey, A. Ovsianikov, R. Liska: "Wavelength-optimized Two-Photon Polymerization Using Initiators Based on Multipolar Aminostyryl-1,3,5-triazines"; Scientific Reports, 8 (2018), S. 1727301 - 1727311.

[7] M. Tromayer, A. Dobos, P. Gruber, A. Ajami, R. Dedic, A. Ovsianikov, R. Liska: "A biocompatible diazosulfonate initiator for direct encapsulation of human stem cells via two-photon polymerization";
Polymer Chemistry, 9 (2018), 22; S. 3108 - 3117.