H-Bonding Room Temperature Phosphorescence Materials via Facile Preparation for Water-Stimulated Photoluminescent Ink.

Pure organic room-temperature phosphorescence (RTP) materials built upon noncovalent interactions have attracted much attention because of their high efficiency, long lifetime, and stimulus-responsive behavior. However, there are limited reports of noncovalent RTP materials because of the lack of specific design principles and clear mechanisms. Here, we report on a noncovalent material prepared via facile grinding that can emit fluorescence and RTP emission differing from their components' photoluminescent behavior. Exciplex can be formed during the preparation process to act as the minimum emission unit. We found that H-bonds in the RTP system provide restriction to nonradiative transition but also enhance energy transformation and energy level degeneracy in the system. Moreover, water-stimulated photoluminescent ink is produced from the materials to achieve double-encryption application with good resolution.

Tunable Fluorescence, Morphology, and Antibacterial Behaviors of Conjugated Oligomers via Host-Guest Supramolecular Self-Assembly.

Host-guest supramolecular self-assembly has become one facile but efficient way to regulate the optical properties of conjugated oligomers and construct promising photofunctional materials. Herein, we design two linear conjugated oligomers terminated with two or four pyridinium moieties, which show different 1:1 'head-to-tail' binding patterns with cucurbit[8]uril (CB[8]) to form host-guest supramolecules. After being encapsulated in the hydrophobic cavity of the CB[8] host, the fluorescence emission of the conjugated oligomers undergoes significant changes, resulting in tunable fluorescence color with enhanced quantum yields. Triggered by the aggregation of supramolecules, the regular or rigid binding modes lead to the formation of cuboids and spheroids in nanoscale, respectively. Due to the macrocyclic-confinement effect, the light-driven reactive oxygen species (ROS) production of the host-guest complex is increased significantly, thereby improving the photodynamic antibacterial performance toward Staphylococcus aureus (S. aureus).

Covalent Organic Frameworks as Efficient Photoinitiators and Cross-Linkers To Fabricate Highly Stretchable Hydrogels.

In this work, two kinds of imine-type covalent organic framework (COF) nanoparticles are demonstrated as efficient photocatalytic initiators to trigger the free-radical polymerization of acrylamide (AM) to prepare polyacrylamide (PAM) hydrogels under visible light irradiation, without any assistance from the co-initiator. Simultaneously, the COF nanoparticles bearing vinyl side groups (COF-V) promote covalent cross-linking of the polymer chains, which significantly reinforces the mechanical properties of the nanocomposite hydrogel. The obtained PAM/COF-V hydrogel is highly stretchable with an extraordinary elongation up to 3300% strain. On the other hand, the COF nanoparticles modified with methoxy moieties (COF-OMe) endow the resulting PAM/COF-OMe hydrogel with a promising fluorescence feature. In addition, this strategy provides a visible-light-regulated photocatalytic polymerization approach with a simplified recipe to fabricate COF-based nanocomposite hydrogels or resins with diverse functions.

In Situ Synthesis of Gold Nanoclusters in Covalent Organic Frameworks with Enhanced Photodynamic Properties and Antibacterial Performance.

In this work, ultrasmall gold nanoclusters (AuNCs) have been in situ synthesized in nanopores of covalent organic framework (COF) nanoparticles, which exhibited enhanced fluorescence, improved photosensitizing capabilities, and promising antibacterial performance. A small organic molecule, 1-vinylimidazole (Vim), was diffused into the nanopores of imine-based COFs and served as a reducing agent and capping ligand for the in situ synthesis of ultrasmall AuNCs. The as-obtained AuNCs were homogeneously distributed throughout the COF nanoparticles whose fluorescence intensity was enhanced remarkably. Due to the efficient electron transfer between AuNCs and COFs and increased separation of photogenerated electron-hole pairs, the light-triggered reactive oxygen species (ROS) production of COFs was prominently enhanced by AuNCs. Moreover, the obtained nanocomposites exhibited an efficient photodynamic killing behavior on Escherichia coli under visible light exposure. Thus, we provide a facile strategy to prepare COF/AuNC nanocomposites for ROS-related applications.

Nanofibre preparation of non-processable polymers by solid-state polymerization of molecularly self-assembled monomers.

Polybisbenzimidazobenzophenanthroline-dione (BBB) is a high-performance polymer which is characterized by very high mechanical strength in combination with exceptional thermal stability, but it cannot be processed to electrospun fibres for any useful applications due to its insolubility and infusibility. We overcame all obstacles in the electrospinning of BBB by a new bottom-up, and facile approach for the solid-state polymerization of self-assembled monomer precursors. Key to this new strategy is the incorporation of a high molecular weight sacrificial polymer to aid in fibre formation. The resulting electrospun BBB fibres and belts prepared thereof according to this new approach are very strong and show excellent thermal stability. We envisage that this procedure could be applied to other classes of non-processable high-performance polymers for the preparation of electrospun fibres for applications such as filtration, sound insulation, battery separation, electrodes, fire protection, and reaction engineering under demanding conditions.