Synthesis of Uniform Polymer Encapsulated Organic Nanocrystals through Ouzo Nanocrystallization

Proper Determination of Phase Diagrams while Nanoprecipitating Oils

The Ouzo effect is a generic process to generate colloidal dispersions from a variety of solutes. Whereas phase diagrams have been quite easily established when nanoprecipitating polymers, the case of oils is less straightforward. Indeed, the short-term stability of generated nanodroplets in water/solvent mixtures complexifies the identification of the diagram boundaries. This article proposes two complementary methods, namely, fluorescence microscopy and dynamic light scattering, to determine with fair accuracy Ouzo limits in ternary systems oil/solvent/nonsolvent, without and with a surfactant, respectively. This accuracy in PD determination opens the way to a better understanding and control of the aggregation events during the nanoprecipitation process.

Multi-Responsive Afterglows from Aqueous Processable Amorphous Polysaccharide Films

Polymer-based room-temperature phosphorescence (RTP) materials, especially polysaccharide-based RTP materials, earn sustained attention in the fields of anti-counterfeiting, data encryption, and optoelectronics owing to their green regeneration, flexibility, and transparency. However, those with both ultralong phosphorescence lifetime and excitation wavelength-dependent afterglow are rarely reported. Herein, a kind of amorphous RTP material with ultralong lifetime of up to 2.52 s is fabricated by covalently bonding sodium alginate (SA) with arylboronic acid in the aqueous phase. The resulting polymer film exhibits distinguished RTP performance with excitation-dependent emissions from cyan to green. Specifically, by co-doping with other fluorescent dyes, further regulation of the afterglow color from cyan to yellowish-green and near-white can be achieved through triplet-to-singlet Förster resonance energy transfer. In addition, the water-sensitive properties of hydrogen bonds endow the RTP property of SA-based materials with water/heat-responsive characteristics. On account of the color-tunable and stimuli-responsive afterglows, these smart materials are successfully applied in data encryption and anti-counterfeiting.

Restriction of molecular motion to a higher level: Towards bright AIE dots for biomedical applications

In the late 19th century, scientists began to study the photophysical differences between chromophores in the solution and aggregate states, which breed the recognition of the prototypical processes of aggregation-caused quenching and aggregation-induced emission (AIE). In particular, the conceptual discovery of the AIE phenomenon has spawned the innovation of luminogenic materials with high emission in the aggregate state based on their unique working principle termed the restriction of intramolecular motion. As AIE luminogens have been practically fabricated into AIE dots for bioimaging, further improvement of their brightness is needed although this is technically challenging. In this review, we surveyed the recent advances in strategic molecular engineering of highly emissive AIE dots, including nanoscale crystallization and matrix-assisted rigidification. We hope that this timely summary can deepen the understanding about the root cause of the high emission of AIE dots and provide inspiration to the rational design of functional aggregates.

Orange/Red Benzo[1,2-b:4,5-b']dithiophene 1,1,5,5-Tetraoxide-Based Emitters for Luminescent Solar Concentrators: Effect of Structures on Fluorescence Properties and Device Performances

Luminescent solar concentrators (LSCs) are a class of optical devices able to harvest, downshift, and concentrate sunlight, thanks to the presence of emitting materials embedded in a polymer matrix. Use of LSCs in combination with silicon-based photovoltaic (PV) devices has been proposed as a viable strategy to enhance their ability to harvest diffuse light and facilitate their integration in the built environment. LSC performances can be improved by employing organic fluorophores with strong light absorption in the center of the solar spectrum and intense, red-shifted emission. In this work, we present the design, synthesis, characterization, and application in LSCs of a series of orange/red organic emitters featuring a benzo[1,2-b:4,5-b']dithiophene 1,1,5,5-tetraoxide central core as an acceptor (A) unit. The latter was connected to different donor (D) and acceptor (A') moieties by means of Pd-catalyzed direct arylation reactions, yielding compounds with either symmetric (D-A-D) or non-symmetric (D-A-A') structures. We found that upon light absorption, the compounds attained excited states with a strong intramolecular charge-transfer character, whose evolution was greatly influenced by the nature of the substituents. In general, symmetric structures showed better photophysical properties for the application in LSCs than their non-symmetric counterparts, and using a donor group of moderate strength such as triphenylamine was found preferable. The best LSC built with these compounds presented photonic (external quantum efficiency of 8.4 ± 0.1%) and PV (device efficiency of 0.94 ± 0.06%) performances close to the state-of-the-art, coupled with a sufficient stability in accelerated aging tests.

Preparation of Ultrasmall AIE Nanoparticles with Tunable Molecular Packing via Freeze Assembly

Advances in the development of aggregation-induced emission luminogens (AIEgens) depend on understanding how the molecular packing affects their luminescent properties and on making nanoparticles (NPs) with desired sizes. Although reported strategies have advanced the field, rational control of molecular packing and efficient fabrication of AIEgen NPs sub-5.5 nm in diameter remain pressing issues. Here we report a "freeze assembly" strategy, in which the diameter of AIEgen NPs can be precisely tuned from ∼3 nm to hundreds of nanometers, and a molecular packing in kinetically trapped states that are not easily captured by conventional assembly methods can be obtained, leading to tunable fluorescence emissions. Therefore, this study provides a significant tool to fabricate organic luminescent nanomaterials with diameters smaller than 5 nm, which is of critical importance for biomedical applications; meanwhile, tuning molecular packing in nanoparticles displaying different fluorescence may help to shed new light on the mechanism of AIEgens.