Abstract
Versatile substituted electron-deficient trichloromethylarenes can easily be synthesized and combined with a Safranine O/triarylalkylborate salt to form a highly efficient three-component photo-initiation system that starts free radical polymerization to finally form holographic gratings with a single-pulsed laser. The mechanism of this photo-initiation most likely relies on an electron transfer from the borate salt into the semi-occupied HOMO of the excited dye molecule Safranine O, which after fragmentation generates an initiating alkyl radical and longer-lived dye radical species. This dye radical is most probably oxidized by the newly introduced trichloromethylarene derivative as an electron acceptor. The two generated radicals from one absorbed photon initiate the photopolymerization and form index gratings in a suitable holographic recording material. This process is purely photonic and does not require further non-photonic post treatments.
Highlights
Polymers 2021, 13, 3517. https://Radiation curable materials have gained significant attention from academic groups as well as from industrial researchers over the last half century [1,2]
In this paper we report on a new highly efficient photo-initiating system (PIS), which consists of three components [9,10]
We report a straightforward method for the comparison of electron acceptors
Summary
Polymers 2021, 13, 3517. https://Radiation curable materials have gained significant attention from academic groups as well as from industrial researchers over the last half century [1,2]. Radiation curable materials have gained significant attention from academic groups as well as from industrial researchers over the last half century [1,2]. Several concepts have been investigated and realized covering the spectral range from extreme UV to the infrared. Because of the unique properties of diffractive optical elements, a material sensitized to visible lights is required in volume holography [3]. Interference patterns are recorded in a photopolymer film with grating distances of approximately 100–1000 nm [4]. The origins of material developments trace back into the 1960s. Silver halide and dichromated gelatine films were used and proved to be valuable for Gabor’s three dimensional recordings of holographic images. Today’s interest is focused on holographic optical elements and their use in compact optical applications. Other areas of interest are the card security and brand protection markets
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