A Simple Preparation of Photoactive Glass Surfaces Allowing Coatings via the "Grafting-from" Method

Organocatalyzed Phospha-Michael Addition: A Highly Efficient Synthesis of Customized Bis(acyl)phosphane Oxide Photoinitiators

Addition of the P-H bond in bis(mesitoyl)phosphine, HP(COMes)₂ (BAPH), to a wide variety of activated carbon-carbon double bonds as acceptors was investigated. While this phospha-Michael addition does not proceed in the absence of an additive or catalyst, excellent results were obtained with stoichiometric basic potassium or caesium salts. Simple amine bases can be employed in catalytic amounts, and tetramethylguanidine (TMG) in particular is an outstanding catalyst that allows the preparation of bis(acyl)phosphines, R-P(COMes)₂ , under very mild conditions in excellent yields after only a short time. All phosphines RP(COMes)₂ can subsequently be oxidized to the corresponding bis(acyl)phosphane oxides, RPO(COMes)₂ , a substance class belonging to the most potent photoinitiators for radical polymerizations known to date. Thus, a simple and highly atom economic method has been found that allows the preparation of a broad range of photoinitiators adapted to their specific field of application even on a large scale.

Macrocyclic Photoinitiator Based on Prism[5]arene Matching LEDs Light with Low Migration

In this work, a naphthalene-based macrocycle prism[5]arene (NP₅ OCH₃ ) is developed as a novel kind of photoinitiator. When NP₅ OCH₃ is irradiated under light, the bond between methylene and naphthalene can be quickly broken owning to the existence of ring tension. The macrocycle is cleaved to linear oligomer biradicals, which can effectively initiate the free radical photopolymerization of acrylate monomers. Compared with conventional photoinitiators, NP₅ OCH₃ has strong light absorption in the wavelength range of 365-405 nm, so it can well match the environment-friendly light-emitting diodes (LEDs) light source to realize highly efficient initiation. In addition, there is no small molecule fragment generated during NP₅ OCH₃ fracture, and the resulted linear oligomer biradicals can be immobilized in the polymer after initiating polymerization, so NP₅ OCH₃ photoinitiators show much lower migration rate and cytotoxicity. Cleavable macrocycle prismarene may provide a new idea for the design of safe and efficient photoinitiators matching long wavelength light.

Covalent Immobilization of Organic Photosensitizers on the Glass Surface: Toward the Formation of the Light-Activated Antimicrobial Nanocoating

Two highly efficient commercial organic photosensitizers—azure A (AA) and 5-(4-aminophenyl)-10,15,20-(triphenyl)porphyrin (APTPP)—were covalently attached to the glass surface to form a photoactive monolayer. The proposed straightforward strategy consists of three steps, i.e., the initial chemical grafting of 3-aminopropyltriethoxysilane (APTES) followed by two chemical postmodification steps. The chemical structure of the resulting mixed monolayer (MIX_TC_APTES@glass) was widely characterized by X-ray photoelectron (XPS) and Raman spectroscopies, while its photoactive properties were investigated in situ by UV–Vis spectroscopy with α-terpinene as a chemical trap. It was shown that both photosensitizers retain their activity toward light-activated generation of reactive oxygen species (ROS) after immobilization on the glassy surface and that the resulting nanolayer shows high stability. Thanks to the complementarity of the spectral properties of AA and APTPP, the effectiveness of the ROS photogeneration under broadband illumination can be optimized. The reported light-activated nanocoating demonstrated promising antimicrobial activity toward Escherichia coli (E. coli), by reducing the number of adhered bacteria compared to the unmodified glass surface.

Hybrid silica micro-particles with light-responsive surface properties and Janus-like character

The present work highlights the synthesis and post-modification of silica-based micro-particles containing photo-responsive polymer brushes with photolabile o-nitrobenzyl ester (o-NBE) chromophores.

Synthesis of γ-cyclodextrin substituted bis(acyl)phosphane oxide derivative (BAPO-γ-CyD) serving as multiple photoinitiator and crosslinking agent

Cyclodextrin with up to 10 bis(acyl)phosphanoxide functions serves as an initiator for highly cross-linked swellable hydrogels from mono-acrylates.

Enabling the synthesis of homogeneous or Janus hairy nanoparticles through surface photoactivation

Nanoparticles (NPs) homogeneously covered with polymer chains or with chains of two different polymers segregated in distinct domains ("Janus" particles) possess remarkable features. Their unique colloidal properties can be finely tuned by the grafted polymers while the characteristics of the nano-core remain unaffected. Herein, a simple and robust photochemical approach is reported to synthesize, from 50 nm cores, homogeneous and Janus "hairy" nanoparticles with hydrophilic and amphiphilic properties, respectively. This is achieved by using a surface-anchored bis(acyl)phosphane oxide photoinitiator which allows a spatially controlled surface-initiated photopolymerization at room temperature. Homogeneous and Janus hairy nanoparticles dispersed in water have very different interaction behaviours which are directly visualized by in situ liquid cell transmission electron microscopy and confirmed by small angle X-ray scattering from a statistically relevant number of particles.

All-in-One Cellulose Nanocrystals for 3D Printing of Nanocomposite Hydrogels

Cellulose nanocrystals (CNCs) with >2000 photoactive groups on each can act as highly efficient initiators for radical polymerizations, cross-linkers, as well as covalently embedded nanofillers for nanocomposite hydrogels. This is achieved by a simple and reliable method for surface modification of CNCs with a photoactive bis(acyl)phosphane oxide derivative. Shape-persistent and free-standing 3D structured objects were printed with a mono-functional methacrylate, showing a superior swelling capacity and improved mechanical properties.

A highly efficient waterborne photoinitiator for visible-light-induced three-dimensional printing of hydrogels

A highly efficient waterborne bis(acyl)phosphane oxide photoinitiator (PEG-BAPO) was conveniently synthesized for 3D printing of hydrogels under blue light irradiation.