Benzylidene Cyclopentanone Derivative Photoinitiator for Two-Photon Photopolymerization-Photochemistry and 3D Structures Fabrication for X-ray Application

Abstract

Micron- and submicron-scale 3D structure realization nowadays is possible due to the two-photon photopolymerization (TPP) direct laser writing photolithography (DLW photolithography) method. However, the achievement of lithographic features with dimensions less than 100 nm is in demand for the fabrication of micro-optical elements with high curvature values, including X-ray microlenses. Spectroscopic and photochemical study of a photoinitiator (PI) based on a methyl methacrylate derivative of 2,5-bis(4-(dimethylamino)benzylidene) cyclopentanone was performed. Enhanced intersystem crossing in the methyl methacrylate derivative results in increased radical generation for the subsequent initiation of polymerization. A comprehensive study of the new photocompositions was performed, with particular emphasis on photochemical constants, the degree of photopolymerization, and topology. The optimal parameters for the fabrication of mechanically stable structures were determined in this research. The threshold dose parameters for lithography (radiation power of 5 mW at a speed of 180 µm/s) when trying to reach saturation values with a conversion degree of (35 ± 1) % were defined, as well as parameters for sub-100 nm feature fabrication. Moreover, the 45 nm feature size for elements was reached. Fabrication of X-ray lens microstructures was also demonstrated.

Do the Laser-Printed 3D-Structures Withstand the X-ray Synchrotron Radiation Beam?

“…The composition contained 49.5% of PETA (Pentaerythritol triacrylate, Sigma-Aldrich), 29.7% of Bis-GMA (bisphenol A-glycidyl methacrylate, Sigma-Aldrich), and 19.8% of TEGDMA (triethylene glycol dimethacrylate, Sigma-Aldrich). A sensitizing dye 4MET-BAC (photoinitiator) [13] was added in the amount of 1%. After the DLW process, the unexposed regions of the composition were removed by washing for 25 min in PEGMA (propylene glycol monomethyl ether acetate), and then for 5 min in IPA (isopropyl alcohol).…”

“…Polymerization of the acrylic-based compositions consumes carbon-carbon double bonds (C═C) for crosslinking. The degree of monomer to polymer conversion (DC) is used to quantify the polymerization efficiency [13,19]. The suggested DC calculation relies upon the ratio of the C═C related peak (1635 cm -1 ) to the C═O related peak (1723 cm -1 ) using the latter as a reference; the decrease of this ratio after laser treatment related to the initial ratio is the measure of DC [13,19].…”

“…The degree of monomer to polymer conversion (DC) is used to quantify the polymerization efficiency [13,19]. The suggested DC calculation relies upon the ratio of the C═C related peak (1635 cm -1 ) to the C═O related peak (1723 cm -1 ) using the latter as a reference; the decrease of this ratio after laser treatment related to the initial ratio is the measure of DC [13,19]. However, we cannot use the same reference peak to estimate the radiation-induced effects: unfortunately, the peak related to C═O chemical bonds also degrades at irradiation.…”

Recent Advances in Monocomponent Visible Light Photoinitiating Systems Based on Sulfonium Salts

“…If this approach is of interest, photons of the visible spectrum exhibit lower energy than UV photons so that visible light photoinitiating systems of higher reactivity should be designed in order to compensate for this reduction of energy. To address this issue, a wide range of structures have been explored as exemplified by camphorquinone [29,30], thiophenes [31], push-pull dyes [2,32,33], anthracenes [34], acridine-1,8-diones [35], benzylidene ketones [36][37][38][39][40][41], chromones and flavones [42][43][44], perylenes [45], diketopyrrolopyrroles [46,47], naphthalimides [48][49][50][51][52][53][54], cyclohexanones [55][56][57][58], chalcones [24,[59][60][61][62][63][64], dithienophosphole derivatives [65], thioxanthones [66][67][68][69][70][71][72...…”