Photoinitiators for two-photon polymerisation: effect of branching and viscosity on polymerisation thresholds

Whitby, Reece; Ben‐Tal, Yael; MacMillan, Ryan; Janssens, S.; Raymond, S. G.; Clarke, Dave; Jin, Jianyong; Kay, Andrew J.; Simpson, M. Cather

doi:10.1039/c6ra27176f

Cited by 26 publications

(25 citation statements)

References 66 publications

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“…Much effort continues to be directed toward developing new radical photoinitiators for MAP, for instance to enable patterning to be faster [ 15–18 ] or to allow for higher resolution. [ 19–23 ] To understand the mechanism of action of a new photoinitiator, it is important to be able to measure the effective order of absorption (EOA) of the material at the excitation wavelength used, i.e., to be able to determine the apparent number of photons that must be absorbed to start the crosslinking process.…”

Section: Introductionmentioning

confidence: 99%

Methods for Determining the Effective Order of Absorption in Radical Multiphoton Photoresists: A Critical Analysis

Λιάρος

Fourkas

2020

Laser & Photonics Reviews

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The accurate determination of the effective order of absorption (EOA) for multiphoton absorption polymerization in radical photoresists is critical for the development and characterization of new materials with improved sensitivity and/or resolution. However, reliable measurement of the EOA is a challenging problem. The accuracy of four techniques that have been developed to address this issue is analyzed in terms of the known kinetics of the radical polymerization of polyfunctional monomers. It is demonstrated that methods that are based upon full reciprocity, i.e., the concept that the chemical response of the photoresist depends on the exposure dose, but not on the period over which this dose is delivered, only enable reliable determination of the EOA under a highly constrained set of circumstances. Methods that depend on limited reciprocity, i.e., the concept that the chemical response of the photoresist is the same when the total exposure window is constant, even if the details of the exposure within that window are varied, can enable accurate determination of the EOA over a considerably broader range of operating conditions. This prediction is verified experimentally. The analysis presented here provides guidance for future experiments and a basis for clearer interpretation of previously published results.

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Section: Introductionmentioning

confidence: 99%

Methods for Determining the Effective Order of Absorption in Radical Multiphoton Photoresists: A Critical Analysis

Λιάρος

Fourkas

2020

Laser & Photonics Reviews

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“…The branched molecules either of quadrupolar or octupolar geometry bear an electron donating or accepting core such as triphenylamine (TPA), 4,5,6,[16][17][18][19][20][21] triazine, 5,9,22,23 truxene [24][25][26][27] etc. Especially,…”

mentioning

confidence: 99%

Photophysical and Protonation Time Resolved Studies of Donor–Acceptor Branched Systems With Pyridine Acceptors

et al. 2018

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A comparative study of the photophysical properties of octupolar pyridyl-terminated triphenylamine molecule, with its quadrupolar and dipolar analogues by means of ambient and low temperature steady state spectroscopy and fs to ns time resolved fluorescence spectroscopy is reported. The push-pull molecules bear triphenylamine electron donating core, pyridine peripheral electron acceptors and acetylenic π-bridge. The samples were studied in solvents of varying polarity and also upon addition of small amounts of acetic acid to induce protonation of the pyridine group. All samples exhibit significant positive fluorescence solvatochromism as well as a relaxation of their excited state to a solvent relaxed Intramolecular Charge Transfer state on the ps timescale. For the octupolar compound, excited state relaxation occurs simultaneously with excitation energy hopping among the branches. The hopping time is solvent polarity controlled since it becomes slower as the polarity increases. The experimental hopping times are compared to those predicted by Förster and Fermi formulations. The samples are capable of emitting broadband light covering almost the whole visible spectrum by careful control of protonation. Energy transfer from the neutral towards the protonated species on the 1 ps timescale is revealed.

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“…[27] Similarly, N,Ndialkyl and -diaryl phenylamines, such as 7 and 8 have also been widely employed in the design of photoinitiators, largely due to their strong electron donating abilities. [10,28] The targeted dialkynyl fluorene 2 was prepared in two-steps via a two-directional Sonogashira cross-coupling of the corresponding dibromo derivative 1 with trimethylsilyl acetylene [29] followed by desilylation with potassium carbonate in methanol (Scheme 2). The azido coupling-partners 7 and 8 were obtained from the corresponding anilines via diazotization and displacement with sodium azide.…”

Section: Photoinitiator Synthesismentioning

confidence: 99%

A Click Chemistry Strategy for the Synthesis of Efficient Photoinitiators for Two‐Photon Polymerization

Henning

Woodward

Rance

et al. 2020

Adv Funct Materials

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It is reported that efficient photoinitiators, suitable for two-photon polymerization, can be obtained using the copper catalyzed azide/alkyne cycloaddition reaction. This click chemistry strategy provides a modular approach to the assembly of photoinitiators that enables the rapid variation of key fragments to produce photoinitiators with desirable properties. To assess the performance of the first-in-class photoinitiators generated by this approach, a screening method is developed to enable the rapid determination of polymerization and damage thresholds in numerous photoresists during two-photon polymerization. The degree of consumption of vinyl groups (DC) and homogeneity of the polymerization are further assessed by micro-Raman spectroscopy. Finally, more complex structures are fabricated to demonstrate that the efficient two-photon polymerization of stable 3D microarchitectures can be achieved using triazole-based photoinitiators.

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Photoinitiators for two-photon polymerisation: effect of branching and viscosity on polymerisation thresholds

Abstract: The effect of the photoinitiator branching on polymerisation thresholds in a series of triphenylamine ethyl ester derivatives is studied.

Cited by 26 publications

References 66 publications

Methods for Determining the Effective Order of Absorption in Radical Multiphoton Photoresists: A Critical Analysis

Methods for Determining the Effective Order of Absorption in Radical Multiphoton Photoresists: A Critical Analysis

Photophysical and Protonation Time Resolved Studies of Donor–Acceptor Branched Systems With Pyridine Acceptors

A Click Chemistry Strategy for the Synthesis of Efficient Photoinitiators for Two‐Photon Polymerization

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