Donor‐Acceptor‐Donor Thienopyrazine‐Based Dyes as NIR‐Emitting AIEgens

A Conjugated Carboranyl Main Chain Polymer with Aggregation-Induced Emission in the Near-Infrared

Materials exhibiting aggregation-induced emission (AIE) are both highly emissive in the solid state and prompt a strongly red-shifted emission and should therefore pose as good candidates toward emerging near-infrared (NIR) applications of organic semiconductors (OSCs). Despite this, very few AIE materials have been reported with significant emissivity past 700 nm. In this work, we elucidate the potential of ortho-carborane as an AIE-active component in the design of NIR-emitting OSCs. By incorporating ortho-carborane in the backbone of a conjugated polymer, a remarkable solid-state photoluminescence quantum yield of 13.4% is achieved, with a photoluminescence maximum of 734 nm. In contrast, the corresponding para and meta isomers exhibited aggregation-caused quenching. The materials are demonstrated for electronic applications through the fabrication of nondoped polymer light-emitting diodes. Devices employing the ortho isomer achieved nearly pure NIR emission, with 86% of emission at wavelengths longer than 700 nm and an electroluminescence maximum at 761 nm, producing a significant light output of 1.37 W sr-1 m-2.

Molecular Engineering Powered Dual-Readout Point-of-Care Testing for Sensitive Detection of Escherichia coli O157:H7

Escherichia coli O157:H7 (E. coli O157:H7) has become one of the major threats to public health and food safety. However, the culture method as a gold standard for the detection of E. coli O157:H7 requires laborious operations and a long processing time. Herein, we developed a dual-readout aggregation-induced emission nanoparticle-based lateral flow immunoassay (LFIA) for sensitive detection of E. coli O157:H7 to achieve a qualitative and quantitative assay for satisfying the applications under varying scenarios. 2,3-Bis(4-(bis(4-(tert-butyl)phenyl)amino)phenyl)fumaronitrile (BAPF), an aggregation-induced emission luminogen, was designed to achieve a strong molar extinction coefficient (3.0 × 104 M-1 cm-1) and high quantum yield (33.28%), which was further verified by a large rotation angle and low energy gap. Subsequently, BAPFs were integrated into a nanostructured system to form excellent water-soluble nanoparticles (BAPFNPs) for the detection of E. coli O157:H7 with colorimetric and fluorescent readout. The designed BAPFNPs-based LFIA (BAPFNPs-LFIA) exhibited nearly qualitative ability with gold nanoparticles-LFIA (AuNPs-LFIA) and a 9 times enhancement compared with quantum beads-LFIA (QBs-LFIA) in quantitative aspect. Especially, FL-BAPFNPs-LFIA could detect E. coli O157:H7 earlier than QBs-LFIA and AuNPs-LFIA when samples with low E. coli O157:H7 concentrations were cultured. Overall, the proposed strategy revealed that versatile BAPFNPs have great potential as reporters for dual-readout ability and enhancing detection sensitivity for rapid and accurate pathogenic bacteria assay.

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.

Red to NIR-emissive anthracene-conjugated PMI dyes with dual functions: singlet-oxygen response and lipid-droplet imaging

The rich chemistry of solution-processable red and near-infrared (NIR) organic emitters has emerged as an attractive and progressive research field because of their particular applications in organic optoelectronics and bioimaging. Also, one can see that the research area of perylene monoimide-based red and NIR-emissive fluorophores is underexplored, which prompted us to design and synthesize three anthracene-conjugated PMI dyes exhibiting strong emission in the red and NIR window in solution. Three PMI-based fluorophores were synthesized via conjoining anthracene and donor moieties (-Ph, -N,N-PhNMe₂) with a PMI core via an acetylene linkage at the peri-position, which helped to attain extensive electronic conjugation, which was reflected in red and NIR-emission in solution. The key molecular features to be highlighted here are: all three dyes are strongly emissive in solution, as unveiled by the excellent absolute fluorescence QYs; and they possess tuneable emission properties, guided by the donor strength and a profound Stokes shift (100-200 nm). The three fluorescent dyes demonstrated appreciable singlet-oxygen (¹O₂) sensitivity when photoirradiated with methylene blue (MB) in solution, showing a substantial blue-shift in emission in a ratiometric manner. Further, the treatment of dye-MB solution with α-tocopherol (¹O₂ scavenger) validated the presence of ¹O₂ as the only oxidizing species generated by MB in solution. Computational investigations gave insight into the twisting of donor moieties in their ground-state optimized geometries, the modulation of the FMO energy gap, and the thermodynamic feasibility of the ¹O₂ reaction. Finally, via taking advantage of the red and NIR-emission, we successfully utilized one of the fluorophores as a lipid-droplet marker for bioimaging in HepG2 cells.

Theoretical Study of Charge-Transfer Exciplexes in Organic Photovoltaics

The photogeneration of charges in bulk heterojunction organic photovoltaics is of crucial importance in the mechanism of charge separation. This results in the formation of both locally excited and charge-transfer exciplex states. While the former states are prone to radiative or nonradiative recombination, the latter ones can have a sufficiently long lifetime. In this work, the formation of charge-transfer exciplex states in pairs of PC61BM (acceptor) with different oligothiophenes (donors) is studied theoretically using density functional theory. The ground and excited states of three oligothiophene-PC61BM complexes are studied. It is found that the intensively absorbing state is localized on the oligothiophene. Another excited state is localized on PC61BM, being characterized by only slight absorption. The charge-transfer (CT) excited state of the complex lies either below or slightly higher than the locally excited (LE) states. The latter case is unfavorable for charge separation. Criteria for the efficient formation of charge-transfer exciplexes are found, and the possibility of oligothiophene modification to facilitate the formation of such exciplexes is explored. Shifting the donor absorption to the near IR, which is important for organic solar cells, is another goal of oligothiophene modification. A modified oligothiophene satisfying these two criteria is proposed. The structure and radiative lifetimes of the LE and CT states and also the binding energy of the CT states with respect to their dissociation into a radical cation and a radical anion are calculated. It is demonstrated that the lifetime of the CT exciplexes is sufficiently long to accomplish charge separation.

Synthesis and Spectroscopic Characterization of Thienopyrazine-Based Fluorophores for Application in Luminescent Solar Concentrators (LSCs)

Organic fluorophores have found broad application as emitters in luminescent solar concentrators (LSCs) for silicon photovoltaics. In particular, the preparation of organic conjugated systems with intense light-harvesting ability, emissions in the deep-red and NIR regions, and large Stokes shift values represent a very challenging undertaking. Here, we report a simple and easy way to prepare three symmetrical donor–acceptor–donor (DAD) organic-emitting materials based on a thienopyrazine core. The central core in the three dyes was modified with the introduction of aromatic substituents, aiming to affect their optical properties. The fluorophores were characterized by spectroscopic studies. In all cases, visible-NIR emissions with large Stokes shifts were found, highlighting these molecules as promising materials for the application in LSCs.