Tailored thioxanthone‐based photoinitiators for two‐photon‐controllable polymerization and nanolithographic printing

Chi, Teng; Somers, Paul; Wilcox, Daniel A.; Schuman, Ashley J.; Iyer, Vasudevan; Le, Ran; Gengler, Jamie; Ferdinandus, Manuel R.; Liebig, Carl M.; Pan, Liang; Xu, Xianfan; Boudouris, Bryan W.

doi:10.1002/polb.24891

Cited by 29 publications

(41 citation statements)

References 41 publications

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“…Indeed, substantial efforts have been dedicated to designing, synthesizing, and characterizing photoinitiator molecules exhibiting large two‐photon‐absorption cross sections at certain wavelengths. [ 23–35 ] However, it has become evident from recent detailed one‐photon‐absorption experiments [ 36 ] that the absorption spectrum versus wavelength may peak at a completely different wavelength than the spectrum of the corresponding light‐induced polymerization rate. [ 36,37 ] Importantly, this surprising and not‐well‐understood finding refers to optically thin samples.…”

Section: Introductionmentioning

confidence: 99%

Sensitive Photoresists for Rapid Multiphoton 3D Laser Micro‐ and Nanoprinting

Wegener

Hahn

Nardi

et al. 2020

Advanced Optical Materials

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parallel projection technologies, [6-8] computed axial lithography as an inverse tomography approach based on multiple 2D optical one-photon exposures from multiple different directions, [9,10] and different forms of multiphoton-absorption 3D printing, [11-16] mostly based on femtosecond or picosecond pulsed lasers. Twophoton lithography has been pioneered by Maruo et al. in 1997. [17] In a few exceptions, continuous-wave (cw) lasers have been used. [18,19] Going "faster" can mean scanning a single focus faster, [20] adapting multiple foci approaches, [21,22] scanning multiple foci faster, [3] or printing more voxels/ pixels in parallel per unit time in projection-based approaches without scanning in the focal plane, [6,7,9,10,12] yet scanning normal to the focal plane. In any case, increasing the printing rate is inherently connected to either using more laser power and the same photoresist, or to using comparable or less laser power by exploiting optimized more sensitive photoresists. As femtosecond or picosecond laser power is a precious commodity associated with a considerable fraction of the cost of most advanced 3D multiphoton laser printers, we dedicate the main part of this contribution to a screening of sensitive multiphoton-absorption-based photo resists. These photoresists are either taken from the published literature, reproduced and remeasured in our labs, or are newly investigated herein as promising candidates. Driven by recent advances in rapid multiphoton single-focus 3D laser nanoprinting, multifocus variants thereof, and projection-based multiphoton 3D laser nanoprinting, the necessary average total laser powers from femtosecond laser oscillators or even from amplified femtosecond laser systems have exceeded the Watt level. Aiming at ever faster 3D printing, there exist two options: Using yet more powerful lasers or searching for more sensitive photoresists allowing for higher speeds at comparable or lower power levels. Here, altogether more than 70 different photoresists from the literature and a few new candidates are reviewed with regard to effective multiphoton sensitivity. A dimensionless sensitivity figure-of-merit allows to directly compare data taken under sometimes vastly different conditions.

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Section: Introductionmentioning

confidence: 99%

Sensitive Photoresists for Rapid Multiphoton 3D Laser Micro‐ and Nanoprinting

Wegener

Hahn

Nardi

et al. 2020

Advanced Optical Materials

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“…The absorption band in the range of 300 to 350 nm and the range of 350 to 380 nm in the UV-vis spectra correspond to the absorption of MCz and TXO, respectively. 37,38 The absorption around 400-450 nm can be attributed to intramolecular CT (ICT) absorption from MCz to TXO and the intensity of ICT absorption of DMCz-TXO is much larger than that of MCz-TXO, although it overlapped partly with the absorption of the TXO at a shorter wavelength. The emission peak maximum wavelength (λ MAX ) was 480 nm for MCz-TXO and 491 nm for DMCz-TXO.…”

Section: Resultsmentioning

confidence: 99%

Thioxanthone-based thermally activated delayed fluorescence emitters showing fast reverse intersystem crossing for efficient organic light-emitting diodes with small efficiency roll-off

Ren

Wada

Suzuki

et al. 2021

Preprint

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Thermally activated delayed fluorescence-based organic light-emitting diodes (TADF OLEDs) usually suffer from severe efficiency roll-off at high brightness which is considered to originate from slow reverse intersystem crossing (RISC) and resulting long-lived triplet excitons. The development of TADF molecules with very fast RISC is an effective approach to overcome this issue. Here, we report two TADF molecules (MCz-TXO, DMCz-TXO) having thioxanthone as an acceptor unit to introduce heavy atom effect. Theoretical calculations predict that both molecules will achieve close energy level matching of the charge-transfer and locally excited triplet states (3CT and 3LE, respectively), together with a small energy gap between 3CT and the lowest excited singlet state. The newly designed molecule, MCz-TXO, showed an extremely large rate constant of RISC (kRISC) of 6.4×107 s− 1, one of the largest kRISC values among all reported pure organic TADF emitters. Moreover, DMCz-TXO showed not only a large kRISC but also a large rate constant of radiative decay both exceeding 107 s− 1, offering a sub-microsecond-scale delayed lifetime (~ 0.8 µs). These thioxanthone-based emitters exhibited great device performances with suppressed efficiency roll-offs at high luminance when applied to OLEDs.

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“…Another limiting factor for achieving high printing rates is the sensitivity of the photoresist. Much work has been done to develop two-photon photoinitiators with improved photoinitiating capabilities [48][49][50][51] .…”

Section: Continuous Layer-by-layer Projection Two-photon Lithography Systemmentioning

confidence: 99%

Rapid, continuous projection multi-photon 3D printing enabled by spatiotemporal focusing of femtosecond pulses

et al. 2021

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There is demand for scaling up 3D printing throughput, especially for the multi-photon 3D printing process that provides sub-micrometer structuring capabilities required in diverse fields. In this work, high-speed projection multi-photon printing is combined with spatiotemporal focusing for fabrication of 3D structures in a rapid, layer-by-layer, and continuous manner. Spatiotemporal focusing confines printing to thin layers, thereby achieving print thicknesses on the micron and sub-micron scale. Through projection of dynamically varying patterns with no pause between patterns, a continuous fabrication process is established. A numerical model for computing spatiotemporal focusing and imaging is also presented which is verified by optical imaging and printing results. Complex 3D structures with smooth features are fabricated, with millimeter scale printing realized at a rate above 10−3 mm3 s−1. This method is further scalable, indicating its potential to make fabrications of 3D structures with micro/nanoscale features in a practical time scale a reality.

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Tailored thioxanthone‐based photoinitiators for two‐photon‐controllable polymerization and nanolithographic printing

Cited by 29 publications

References 41 publications

Sensitive Photoresists for Rapid Multiphoton 3D Laser Micro‐ and Nanoprinting

Sensitive Photoresists for Rapid Multiphoton 3D Laser Micro‐ and Nanoprinting

Thioxanthone-based thermally activated delayed fluorescence emitters showing fast reverse intersystem crossing for efficient organic light-emitting diodes with small efficiency roll-off

Rapid, continuous projection multi-photon 3D printing enabled by spatiotemporal focusing of femtosecond pulses

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