π-Conjugated Polymers Composed of BODIPY or Aza-BODIPY Derivatives Exhibiting High Electron Mobility and Low Threshold Voltage in Electron-Only Devices

Naphthalene Monoanhydride and Perylene Composites for Efficient Photocatalytic Hydrogen Evolution and Metal-Free Heterogeneous Oxidative Amidation

This study explores the synthesis of two visible light active organic chromophore-based composites using naphthalene monoanhydride (Np) and 1,7-dibromoperylene monoanhydride diester (PMDE). These chromophores feature favorable optical and electronic properties and polyaromatic skeletons with anhydride functionalities that facilitate π-π interactions between the chromophore and polymeric carbon nitride (CN) or covalent connections of chromophores with NH2 groups of CN. Accordingly, heterogeneous chromophore-CN composite photocatalysts namely, Np/CN(c) and PMDE/CN(c) were prepared by adopting in situ calcination (c) and composites Np/CN(a) and PMDE/CN(a) were prepared by ex situ physical adsorption (a) methods. In situ prepared Np/CN(c) and PMDE/CN(c) composites exhibited H2 evolution rates (HER) of 1069 and 705 μmol h-1 g-1, respectively, which are significantly higher than ex situ Np/CN(a) and PMDE/CN(a) composites with HER of 465 and 252 μmol h-1 g-1, respectively. These rates are 10, 7, 4.8, and 2.5 times higher than the bulk-CN, indicating the potential of these composites for efficient photocatalytic H2 evolution. Surface area normalized HER enhancements were 3.8, 5.3, 6.6, and 4.2 times higher for Np/CN(c), PMDE/CN(c), Np/CN(a), and PMDE/CN(a) respectively compared to bulk-CN. These composite photocatalysts exhibited excellent stabilities under prolonged photoirradiation, with H2 evolution consistently increasing with the light exposure time. Additionally, these metal-free heterogeneous composites demonstrated efficient photocatalytic activities towards oxidative amidation of aromatic aldehydes, with up to 80% product yields, establishing the prospects of combining homogeneous and heterogeneous entities in a metal-free active material in solar energy harvesting.

Molecular rotors of naphthalimide and benzodithiophene as effective solvent polarity probes, temperature sensors, and for g-C3N4 sensitization

Acceptor-donor-acceptor (A-D-A) molecular rotors have drawn substantial attention for their applications in monitoring temperature variations within cellular microenvironments, biomimetic photocatalysis, and bioimaging. In this study, we have synthesized two novel rotor molecules, NBN1 and NBN2, by incorporating benzodithiophene (BDT) as the donor core and naphthalic anhydride/naphthalimide (NA/NI) moieties as acceptors using Pd-catalyzed Stille coupling reactions. These molecules exhibited distinct charge transfer (CT) behavior in both their absorption and emission spectra and displayed prominent emission solvatochromism. Notably, NBN1 exhibited better CT properties among the two molecules. Moreover, these A-D-A molecular rotors demonstrated remarkable sensitivities of their emission spectra toward solvent polarities and temperatures. Rotors NBN1 and NBN2 showed positive temperature coefficients with internal temperature sensitivities of 0.34% °C-1 and 0.13% °C-1 in chloroform, respectively, and thus hold significant promise for detecting temperature variations in cellular microenvironment. Furthermore, we have modeled these molecules with graphitic carbon nitride (g-C3N4) to form composite systems and performed theoretical calculations to obtain valuable insights into their charge transfer behavior. Theoretical results suggested that these molecules have the potential to efficiently sensitize and modulate the band gap of g-C3N4 and show potential for diverse photocatalytic applications.

Near-Infrared Emissive Hypervalent Compounds with Germanium(IV)-Fused Azobenzene π-Conjugated Systems

A novel molecular design for showing near-infrared (NIR) emission is still required for satisfying growing demands for NIR-light technology. In this research, hypervalent compounds with germanium (Ge)-fused azobenzene (GAz) scaffolds were discovered that can exhibit NIR emission (λ_PL =690∼721 nm, Φ_PL =0.03∼0.04) despite compact π-conjugated systems. The unique optical properties are derived from the trigonal bipyramidal geometry of the hypervalent compounds constructed by combination of Ge and azobenzene-based tridentate ligands. Experimental and theoretical calculation results disclosed that the germanium-nitrogen (Ge-N) coordination at the equatorial position strongly reduces the energy level of the LUMO (lowest unoccupied molecular orbital), and the three-center four-electron (3 c-4 e) bond in the apical position effectively rises the energy level of the HOMO (highest occupied molecular orbital). It is emphasized that large narrowing of the HOMO-LUMO energy gap is achieved just by forming the hypervalent bond. In addition, the narrow-energy-gap property can be enhanced by extension of π-conjugation. The obtained π-conjugated polymer shows efficient NIR emission both in solution (λ_PL =770 nm and Φ_PL =0.10) and film (λ_PL =807 nm and Φ_PL =0.04). These results suggest that collaboration of a hypervalent bond and a π-conjugated system is a novel and effective strategy for tuning electronic properties even in the NIR region.

Effect of conjugated system extension on structural features and electron-density distribution in charge-transfer difluoroborates

A comparative structural study of two related donor-acceptor pyridine-based BF₂ complexes, namely, 3-(dimethylamino)-1,1-difluoro-1H-pyrido[1,2-c][1,3,5,2]oxadiazaborinin-9-ium-1-uide, C₈H₁₀BF₂N₃O (1), and 3-{(1E,3E)-4-[4-(dimethylamino)phenyl]buta-1,3-dien-1-yl}-1,1-difluoro-1H-pyrido[1,2-c][1,3,5,2]oxadiazaborinin-9-ium-1-uide, C₁₈H₁₈BF₂N₃O (2), containing a dimethylamino group and either the shortest (in 1) or the longest (in 2) charge-transfer path known until now in this family of compounds, is presented. Single-crystal X-ray diffraction analysis supported by computational investigations shed more light on these systems, indicating, among other aspects, the predominance of C-H...F contacts in 1, the formation of antiparallel dimers held together by π-π interactions in both compounds, and the involvement of fused BF₂-bearing rings in the charge-transfer process.

Double 3-Ethyl-2,4-dimethylpyrrole Configured Fluorescent Dye with Fluorine-Boron as the Bridge

Dipyrrolydiketones BF₂ complex was synthesized and characterized by NMR, HRMS, and single crystal diffraction. In non-polar environment, this BF₂ containing dye emitted bright blue-green fluorescence. No significant spectra shift was observed both in absorption and emission spectra, which indicates the insensitivity of absorption/emission toward environment. The alkyl substituted pyrrole rings lead to its highly emission character in solid state by enhancing the distance between dye molecules. Absolute quantum yields were determined to be 0.51-0.78/0.36 in selected organic medium and solid state, respectively. The emission dynamics was investigated by fluorescence lifetime and both monoexponential and bi-exponential decay was observed.

Electron Transport in Naphthalene Diimide Derivatives

Two naphthalene diimides derivatives containing two different (alkyl and alkoxyphenyl) N-substituents were studied, namely, N,N′-bis(sec-butyl)-1,4,5,8-naphthalenetetracarboxylic acid diimide (NDI-s-Bu) and N,N′-bis(4-n-hexyloxyphenyl)-1,4,5,8-naphthalenetetracarboxylic acid diimide (NDI-4-n-OHePh). These compounds are known to exhibit electron transport due to their electron-deficient character evidenced by high electron affinity (EA) values, determined by electrochemical methods and a low-lying lowest unoccupied molecular orbital (LUMO) level, predicted by density functional theory (DFT) calculations. These parameters make the studied organic semiconductors stable in operating conditions and resistant to electron trapping, facilitating, in this manner, electron transport in thin solid layers. Current–voltage characteristics, obtained for the manufactured electron-only devices operating in the low voltage range, yielded mobilities of 4.3 × 10⁻⁴ cm²V⁻¹s⁻¹ and 4.6 × 10⁻⁶ cm²V⁻¹s⁻¹ for (NDI-s-Bu) and (NDI-4-n-OHePh), respectively. Their electron transport characteristics were described using the drift–diffusion model. The studied organic semiconductors can be considered as excellent candidates for the electron transporting layers in organic photovoltaic cells and light-emitting diodes

Highly stable organic photothermal agent based on near-infrared-II fluorophores for tumor treatment

BACKGROUND

The aim to develop a highly stable near-infrared (NIR) photoinduced tumor therapy agent stems from its considerable potential for biological application. Due to its long wavelength, biological imaging exhibits a high signal-to-background ratio, deep tissue penetration and maximum permissible light power, which can minimize damage to an organism during photoinduced tumor therapy.

RESULTS

A class of stable NIR-II fluorophores (NIR998, NIR1028, NIR980, NIR1030, and NIR1028-S) based on aza-boron-dipyrromethene (aza-BODIPY) dyes with donor-acceptor-donor structures have been rationally designed and synthesized by harnessing the steric relaxation effect and intramolecular photoinduced electron transfer (IPET). These fluorophores exhibit an intense range of NIR-II emission, large Stokes shift (≥ 100 nm), excellent photothermal conversion performance, and superior stability against photobleaching. Among the NIR-II fluorophores, NIR998 possesses better NIR-II emission and photothermal conversion performance. NIR998 nanoparticles (NIR998 NPs) can be encapsulated by liposomes. NIR998 NPs show superior stability in the presence of light, heat, and reactive oxygen nitrogen species than that of indocyanine green NPs, as well as a higher photothermal conversion ability (η = 50.5%) compared to other photothermal agents. Finally, under the guidance of photothermal imaging, NIR998 NPs have been proven to effectively eliminate tumors via their excellent photothermal conversion performance while presenting negligible cytotoxicity.

CONCLUSIONS

Utilizing IPET and the steric relaxation effect can effectively induce NIR-II emission of aza-BODIPY dyes. Stable NIR998 NPs have excellent photothermal conversion performance and negligible dark cytotoxicity, so they have the potential to act as photothermal agents in biological applications.

Boron dipyrromethene (BODIPY) in polymer chemistry

The present review provides both a summary and outlook on the exciting field of BODIPYs in polymer chemistry.

Architectures and Applications of BODIPY-Based Conjugated Polymers

Conjugated polymers generally contain conjugated backbone structures with benzene, heterocycle, double bond, or triple bond, so that they have properties similar to semiconductors and even conductors. Their energy band gap is very small and can be adjusted via chemical doping, allowing for excellent photoelectric properties. To obtain prominent conjugated materials, numerous well-designed polymer backbones have been reported, such as polyphenylenevinylene, polyphenylene acetylene, polycarbazole, and polyfluorene. 4,4'-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-based conjugated polymers have also been prepared owing to its conjugated structure and intriguing optical properties, including high absorption coefficients, excellent thermal/photochemical stability, and high quantum yield. Most importantly, the properties of BODIPYs can be easily tuned by chemical modification on the dipyrromethene core, which endows the conjugated polymers with multiple functionalities. In this paper, BODIPY-based conjugated polymers are reviewed, focusing on their structures and applications. The forms of BODIPY-based conjugated polymers include linear, coiled, and porous structures, and their structure-property relationship is explored. Also, typical applications in optoelectronic materials, sensors, gas/energy storage, biotherapy, and bioimaging are presented and discussed in detail. Finally, the review provides an insight into the challenges in the development of BODIPY-based conjugated polymers.

Highly selective ratiometric fluorescent probes for the detection of Fe3+ and its application in living cells

It's of vital importance to detect heavy metals in environment and living cells. In this work, four near-infrared regions boron dipyrromethene (BODIPY) probes (QBPH, PBPH, QBP and PBP) are constructed based on two BODIPY precursors (QB, PB) for sensing of Fe³⁺. As expected, these four probes exhibit obvious colorimetric and ratiometric response to Fe³⁺. In addition, QBP and PBP display highly sensitive and selective performance for detection of Fe³⁺. More importantly, QBP and PBP are successfully applied to near infrared imaging and detection of Fe³⁺ in living A549 cells; it indicates that these novel designed probes could be a useful tool for the studies of Fe³⁺ in living cells.

Unique Substitution Effect at 5,5'-Positions of Fused Azobenzene-Boron Complexes with a N=N π-Conjugated System

A recent report illustrated superior optical properties, such as near-infrared emission, of polymers connected at the 4,4'-positions to a fused azobenzene-boron complex (BAz). In this study, it is initially demonstrated that further narrowing of the band gap can be realized through the substituent effect with bromine groups at the 5,5'-positions of BAz compared with those at the 4,4'-positions. From a series of mechanistic studies, perturbation of the energy levels was rationally explained by the difference in contributions of the inductive effect and the variable resonance effect, which was correlated with the degree of electron distribution of molecular orbitals at the substituent positions. Moreover, it was found that unique electronic states, such as delocalized HOMOs and LUMOs, should appear on the main chains of the BAz-containing copolymers with fluorene and bithiophene units, according to the optical and electrochemical data and theoretical calculations. By taking advantage of property tunability and the dramatically low LUMO energy level (near -4.0 eV) of the BAz unit, it can be said that BAz should be a conjugated building block favorable for building advanced optoelectronic devices.

Surfactant-Stripped Micelles of Near Infrared Dye and Paclitaxel for Photoacoustic Imaging Guided Photothermal-Chemotherapy

Development of nanoagents with strong near-infrared (NIR) absorbance and high photothermal conversion capacity is highly desired for efficient photoacoustic (PA) imaging and photothermal therapy of cancers. Herein, surfactant-stripped micelles with photostable near-infrared dye, β-thiophene-fused BF₂ -azadipyrromethene (aza-BDTP), are prepared in the presence of paclitaxel (PTX) with Pluronic F127 as the surfactant. Distinct from hydrophobic aza-BDTP and PTX, the obtained surfactant-stripped micelles aza-BDTP/PTX show excellent solubility, physiological stability, and high loading efficiencies for corresponding aza-BDTP and PTX. Intriguingly, these aza-BDTP/PTX micelles exhibit high photothermal conversion efficiency at 33.9%, significantly higher than 16.9% for bare aza-BDTP molecules, owing to aggregation-induced quenching of aza-BDTP fluorescence. With excellent photostability, aza-BDTP/PTX micelles appear to be a highly stable photoacoustic imaging probe and show efficient tumor accumulation as visualized under photoacoustic imaging upon intravenous injection. After being irradiated with a 785 nm laser, 4T1 tumors on the mice with systemic administration of aza-BDTP/PTX micelles are fully eradiated without any recurrences within 60 d. This work presents a general method for efficient encapsulation of hydrophobic aza-BDTP and PTX, obtaining hybrid aza-BDTP/PTX micelles as promising nanotheranostics for imaging guided cancer combination therapy.

Aza-BODIPY based polymeric nanoparticles for cancer cell imaging

Near infrared (NIR) fluorescent dyes that are widely used for cancer imaging usually suffer from their hydrophobicity. To overcome this problem, a water-suspendable and biodegradable NIR-light-activating aza-BODIPY (AZB-NO₂) encapsulated in polymeric nanoparticles was prepared as a new class of deep-tissue imaging agent. AZB-NO₂ possesses an intense, broad NIR absorption band (600–800 nm) with a remarkably high fluorescent quantum yield. After being encapsulated with a biodegradable polycaprolactone (PCL) and a Kolliphor P188 surfactant by emulsification-solvent evaporation method, the AZB-NO₂ formed a spherical shape as observed in scanning electron micrographs (SEM) with a hydrodynamic average size of 201 nm (average PDI = 0.185). The results from transmission electron micrographs (TEM) and energy dispersive X-ray spectroscopy (EDS) elemental mapping indicated that the AZB-NO₂ homogeneously distributed in the polymeric shell. UV-visible-NIR and fluorescence spectra of the obtained nanoparticles, AZB-NO₂@PCL, revealed that the nanoparticles prepared by using 0.8 mg dye loading exhibited the highest fluorescence quantum yield. These nanoparticles were then applied for fluorescence imaging in human glioblastoma cell line (U-251). After the cells were exposed to AZB-NO₂@PCL, the materials appeared to be localized inside U-251 cells within 3 h and the fluorescence signal enhanced along with the increased incubation times. Moreover, 3D cell culture was used in this study to mimic in vivo tumor environments. The AZB-NO₂@PCL exhibited bright fluorescence from U-251 cells inside 3D Ca-alginate scaffolds after 24 h incubation. Our study successfully demonstrated that the encapsulation of hydrophobic aza-BODIPY dye could enhance the water-suspendability of the dye yielding biocompatible nanoparticles efficiently used in cancer cell imaging applications.

Encapsulation of hydrophobic aza-BODIPY dye could enhance its hydrophilicity yielding biocompatible nanoparticles which can be efficiently used in cancer cell imaging applications.

Pure-color and dual-color emission from BODIPY homopolymers containing the cardo boron structure

Pure-color and dual-color emission were accomplished with homopolymers composed of modified boron dipyrromethene involving cardo boron.

2D and 3D surface photopatterning via laser-promoted homopolymerization of a perfluorophenyl azide-substituted BODIPY

An innovative photopatterning process is described that allows, in a single laser-promoted operation, the covalent attachment of a molecule on a surface (2D patterning - xy dimensions) and its photopolymerization to grow micro-/nanostructures with spatial control in a third z-dimension. The surface patterning process, based on nitrene reactivity, was harnessed using the highly fluorescent azide-substituted boron difluoride dipyrromethene (BODIPY) 1 that was prepared in a single synthetic step from the parent pentafluorophenyl BODIPY on reacting with NaN₃. Using the laser of a fluorescence microscope (375 nm or 532 nm) 1 could be grafted on adapted surfaces and then homopolymerised. In this study we show that using glass coverslips coated with PEG/high density alkyne groups (density of ∼1 × 10¹⁴ per cm²), the patterning process was much more spatially confined than when using PEG only coating. Varying the irradiation time (1 to 15 s) or laser power (0.14-3.53 μW) allowed variation of the amount of deposited BODIPY to afford, in the extreme case, pillars of a height up to 800 nm. AFM and MS studies revealed that the nano/microstructures were formed of particles of photopolymerized 1 having a mean diameter of ca. 30 nm. The emission spectra and fluorescence lifetimes for the patterned structures were measured, revealing a red-shift (from ∼560 nm up to 620 nm) of the maximum emission and a shortening (from ∼6 ns to 0.8 ns) of the fluorescence lifetimes in areas where the density of BODIPY is high. As an application of the patterning process, a figure formed of 136 dots/pillars was prepared. The confocal hyperspectral fluorescence image revealed that the figure is clearly resolved and constituted by highly photoluminescent red dots whose fluorescence intensities and emission color proved to be highly reproducible. SEM and AFM studies showed that the luminescent dots were pillars with a conical shape, an average height of 710 ± 28 nm and a FWHM of 400 ± 20 nm.

Synthesis of Aggregation-Induced Emission-Active Conjugated Polymers Composed of Group 13 Diiminate Complexes with Tunable Energy Levels via Alteration of Central Element

Conjugated polymers containing boron and gallium diiminate complexes were prepared with various electron-donating comonomers via pre- and post-complexation methods, respectively. From a comparison of emission quantum yields between solution and film states, it was seen that all polymers containing group 13 elements possessed an aggregation-induced emission property. Additionally, the frontier orbital energies and the optical and electrochemical properties of the polymers can be tuned by altering a central element at the complex moieties as well as by changing a comonomer unit. In particular, it was demonstrated that the gallium atom can contribute to stabilizing the energy levels of the lowest unoccupied molecular orbitals, resulting in narrow band gaps of the conjugated polymers. This study presents the potential of gallium not only for preparing solid-state emissive conjugated polymers but also for fabricating low-band gap materials by employing the conjugated ligand.

Photophysics and redox properties of aza-BODIPY dyes with electron-withdrawing groups

The optical and electrochemical properties are compared for aza-BODIPY dyes that differ by virtue of the substituents at 1,7- and 3,5-positions of the aza-BODIPY backbone.

Construction and properties of a light-harvesting antenna system for phosphorescent materials based on oligofluorene-tethered Pt–porphyrins

Tetramerous molecular assemblies composed of four oligofluorenes as a light-harvesting antenna (LHA) and a Pt–porphyrin core as a phosphorescent chromophore were designed and synthesized for obtaining efficient phosphorescent materials.

Development of solid-state emissive o-carboranes and theoretical investigation of the mechanism of the aggregation-induced emission behaviors of organoboron “element-blocks”

This paper presents the aggregation-induced emission (AIE) properties of o-carborane derivatives and proposes a potential strategy for constructing AIE-active organoboron complexes via the enhancement of freedom of intramolecular mobility. Initially, the optical properties of o-carborane derivatives with or without the fused ring structure at the C–C bond in o-carborane in which elongation should be induced by photo-excitation according to theoretical calculations were compared. Accordingly, it was shown that large mobility at the C–C bond in o-carborane should be responsible for the annihilation of emission in solution, leading to the AIE property. From this result, it was presumed that by enhancing the freedom of intramolecular mobility in conventional luminescent organoboron complexes, the deactivation of the excited state in solution and emission recovery in the aggregate can be induced. Based on this idea, we have performed several studies and introduce two representative results. Firstly, the decrease in luminescent properties of boron dipyrromethene (BODIPY) in solution by introducing a movable functional group is explained. Next, the AIE behaviors of boron ketoiminates and the potential mechanism concerning conformational changes for the deactivation of the excited state in the solution state are illustrated. It is proposed that enhancement of the freedom of mobility in the excited state of luminescent organoboron complexes could be a potential strategy for realizing AIE behaviors.

Preservation of main-chain conjugation through BODIPY-containing alternating polymers from electronic interactions with side-chain substituents by cardo boron structures

This manuscript describes the synthesis and electronic structures of the modified boron dipyrromethene derivatives containing cardo boron.

Azadipyrromethenes: from traditional dye chemistry to leading edge applications

The journey of azadipyrromethenes from accidental dye chemistry to a compound class with widely applicable near infrared photophysical properties is documented.

Synthesis, Luminescent Properties of aza-Boron-Diquinomethene Difluoride Complexes and Their Application for Fluorescent Security Inks

Two aza-boron-diquinomethene (aza-BODIQU) complexes bearing phenyl and carbazyl substituents were synthesized and characterized. Their photophysical properties were investigated systematically via spectroscopic and theoretical methods. Both complexes exhibit strong (1)π-π* transition absorptions (λ(abs) = 400-540 nm) and intense fluorescent emissions (λ(em) = 440-600 nm, Φ(PL) = 0.93 and 0.78) in CH2Cl2 solution and in solid state at room temperature. Compared to the complex with phenyl groups, the complex bearing carbazyl groups shows significant bathochromic shift in both absorption and emission. This could be attributed to the larger π-electron conjugation of the carbazole unit and intramolecular charge transfer feature from carbazole to aza-BODIQU component. In addition, the complexes exhibit intense photoluminescence and good stability on antacid, anti-alkali and stability in printing ink samples, which makes them potential dopants for the application of fluorescent security inks.

Liquid scintillators with near infrared emission based on organoboron conjugated polymers

The organic liquid scintillators based on the emissive polymers are reported. A series of conjugated polymers containing organoboron complexes which show the luminescence in the near infrared (NIR) region were synthesized. The polymers showed good solubility in common organic solvents. From the comparison of the luminescent properties of the synthesized polymers between optical and radiation excitation, similar emission bands were detected. In addition, less significant degradation was observed. These data propose that the organoboron conjugated polymers are attractive platforms to work as an organic liquid scintillator with the emission in the NIR region.

Polymers and the p-block elements

A survey of the state-of-the-art in the development of synthetic methods to incorporate p-block elements into polymers is given. The incorporation of main group elements (groups 13-16) into long chains provides access to materials with fascinating chemical and physical properties imparted by the presence of inorganic groups. Perhaps the greatest impedance to the widespread academic and commercial use of p-block element-containing macromolecules is the synthetic challenge associated with linking inorganic elements into long chains. In recent years, creative methodologies have been developed to incorporate heteroatoms into polymeric structures, with perhaps the greatest advances occurring with hybrid organic-inorganic polymers composed of boron, silicon, phosphorus and sulfur. With these developments, materials are currently being realized that possess exciting chemical, photophysical and thermal properties that are not possible for conventional organic polymers. This review focuses on highlighting the most significant recent advances whilst giving an appropriate background for the general reader. Of particular focus will be advances made over the last two decades, with emphasis on the novel synthetic methodologies employed.