Advances in Light-Emitting Dendrimers

Organic Heterostructures with Dendrimer Based Mixed Layer for Electronic Applications

Recently, much research has focused on the search for new mixed donor-acceptor layers for applications in organic electronics. Organic heterostructures with layers based on the generation 1 poly(propylene thiophenoimine) (G1PPT) dendrimer, N,N'-diisopropylnaphthalene diimide (MNDI), and a combination of the two were prepared and their electrical properties were investigated. Single layers of G1PPT and MNDI and a mixed layer (G1PPT:MNDI) were obtained via spin coating on quartz glass, silicon, and glass/ITO substrates, using chloroform as a solvent. The absorption mechanism was investigated, the degree of disorder was estimated, and the emission properties of the layers were highlighted using spectroscopic methods (UV-Vis transmission and photoluminescence). The effects of the concentration and surface topographical particularities on the properties of the layers were analyzed via atomic force microscopy. All of the heterostructures realized with ITO and Au electrodes showed good conduction, with currents of the order of mA. Additionally, the heterostructure with a mixed layer exhibited asymmetry in the current-voltage curve between forward and reverse polarization in the lower range of the applied voltages, which was more significant at increased concentrations and could be correlated with rectifier diode behavior. Consequently, the mixed-layer generation 1 poly(propylene thiophenoimine) dendrimer with N,N'-diisopropylnaphthalene diimide can be considered promising for electronic applications.

Using a Dendritic Sensor as a Feasible Method for Detection of Copper in Water Samples

Due to the severe dangers of copper on human health, development of identification and measurement copper methods in aquatic environments as well as prevention transfer methods of these substances to water resources have received much attention. Among of this expansion, rapid, simple, safe, sensitive and economically viable detection methods are more considerable. In this paper, the sensor activity of the poly(amidoamine) dendrimer containing eight methoxy groups modified with naphthalimide fluorescent derivative is studied. The sensor potential of dendrimer-naphthalimide fluorescence was evaluated in various solvents with different polarities, and results indicated that the detection of cuprum cations (Cu²⁺) is possible at low concentration. Also, the fluorescence properties of dendrimer-naphthalimide system are measured in the presence of diverse metal cations. In light of above, from the obtaining results, it can be concluded that dendritic sensor can be used as a feasible method to detect of copper in water samples in low concentrations.

Cibalackrot Dendrimers for Hyperfluorescent Organic Light-Emitting Diodes

Hyperfluorescent organic light-emitting diodes (HF-OLEDs) enable a cascading Förster resonance energy transfer (FRET) from a suitable thermally activated delayed fluorescent (TADF) assistant host to a fluorescent end-emitter to give efficient OLEDs with relatively narrowed electroluminescence compared to TADF-OLEDs. Efficient HF-OLEDs require optimal FRET with minimum triplet diffusion via Dexter-type energy transfer (DET) from the TADF assistant host to the fluorescent end-emitter. To hinder DET, steric protection of the end-emitters has been proposed to disrupt triplet energy transfer. In this work, the first HF-OLEDs based on structurally well-defined macromolecules, dendrimers is reported. The dendrimers contain new highly twisted dendrons attached to a Cibalackrot core, resulting in high solubility in organic solvents. HF-OLEDs based on dendrimer blend films are fabricated to show external quantum efficiencies of >10% at 100 cd m^-2 . Importantly, dendronization with the bulky dendrons is found to have no negative impact to the FRET efficiency, indicating the excellent potential of the dendritic macromolecular motifs for HF-OLEDs. To fully prevent the undesired triplet diffusion, Cibalackrot dendrimers HF-OLEDs are expected to be further improved by adding additional dendrons to the Cibalackrot core and/or increasing dendrimer generations.

Dendronized Porphyrins: Molecular Design and Synthesis

Abstract:

In this review, we report different methods and strategies to synthesize flexible and rigid dendronized porphyrins. We will focus on porphyrin dendrimers that have been reported in the last 10 years. Particularly, in our research group, we have designed and synthesized different series of dendronized porphyrins (free base and metallated) with pyrene units at the periphery and Fréchet-type dendritic arms. The Lindsey methodology has allowed the synthesis of meso-substituted porphyrins with various substitution patterns, such as symmetric, dissymmetric, or unsymmetric. Porphyrin dendrimers have been prepared by different synthetic methodologies; one of the most reported being the convergent method, where the dendrons are first prepared and further linked to a meso-substituted functionalized porphyrin unit, which will constitute the core of the dendrimer. Another interesting synthetic approach is the use of a reactive dendron bearing a terminal aldehyde functional group to form the final porphyrin core. In this way, a two-armed dendronized dissymmetric porphyrin core can be prepared from a dendritic precursor and a dipyrromethene derivative. This strategy is very convenient to prepare low-generation dendritic porphyrins. The divergent approach is another well-known methodology for porphyrin dendrimer synthesis, mostly used for the obtainment of high-generation dendrimers. Click chemistry reaction has been advantageous for the development of more complex porphyrin dendritic structures. This reaction presents important advantages, such as high yields and mild reaction conditions which permit the assembly of different multiporphyrin dendritic structures. In the constructs presented in this review, the emission of the porphyrin moiety has been observed, leading to potential applications in artificial photosynthesis, sensing, nanomedicine, and biological sciences.

Review of photoresponsive and glycoside dendrimers in biomaterials and sensors applications

Dendrimers are branched molecules with well-defined lengths, shapes, molecular weights, and monodispersity in comparison to linear polymers.

Dendritic polyphenylene AIEgens: fluorescence detection of explosives and stimulus-responsive luminescence

Dendritic AIEgens with polyphenylene peripherals and TPE luminescent core had shown detection capability to picric acid and tunable response to external stimulus.

Aggregation-Induced Emission Properties in Fully π-Conjugated Polymers, Dendrimers, and Oligomers

Aggregation-Induced Emission (AIE) in organic molecules has recently attracted the attention of the scientific community because of their potential applications in different fields. Compared to small molecules, little attention has been paid to polymers and oligomers that exhibit AIE, despite having excellent properties such as high emission efficiency in aggregate and solid states, signal amplification effect, good processability and the availability of multiple functionalization sites. In addition to these features, if the molecular structure is fully conjugated, intramolecular electronic interactions between the composing chromophores may appear, thus giving rise to a wealth of new photophysical properties. In this review, we focus on selected fully conjugated oligomers, dendrimers and polymers, and briefly summarize their synthetic routes, fluorescence properties and potential applications. An exhaustive comparison between spectroscopic results in solution and aggregates or in solid state has been collected in almost all examples, and an opinion on the future direction of the field is briefly stated.

Pharmacological Evaluation of Novel Organoiron Dendrimers as Antimicrobial and Anti-Inflammatory Agents

The synthesis of a novel and attractive class of nonsteroidal anti-inflammatory and antimicrobial organoiron dendrimers attached to the well-known drug ibuprofen is achieved. The structures of these dendrimers are established by spectroscopic and analytical techniques. The antimicrobial activity of these dendrimers is investigated and tested against five human pathogenic Gram-positive and Gram-negative bacteria, and minimum inhibitory concentrations are reported. Some of these synthesized dendrimers exhibit higher inhibitory activity against methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecium, and Staphylococcus warneri compare to the reference drugs. As well, the in vitro and in vivo anti-inflammatory activities of these dendrimers are evaluated. The results of in vivo anti-inflammatory activity and histopathology of inflamed paws show that all dendrimers display considerable anti-inflammatory activity; however, second-generation dendrimer (G2-D6) shows the best anti-inflammatory activity, which is more potent than the commercial drug ibuprofen at the same tested dose. Results of the toxicity study reveal that G2-D6 is the safest drug on biological tissues.

Synthetic strategies tailoring colours in multichromophoric organic nanostructures

Mimicking nature to develop light-harvesting materials is a timely challenge. This tutorial review examines the chemical strategies to engineer and customise innovative multi-coloured architectures with specific light-absorbing and emitting properties.

Design, Synthesis and Self-Assembly of Functional Amphiphilic Metallodendrimers

A new family of alkynylated, amphiphilic dendrimers consisting of amidoamine linkers connected to 5,5'-functionalized 2,2'-bipyridine cores has been developed and evaluated in the formation of metallodendrimers of different generations and in self-assembly protocols. A convergent synthetic strategy was applied to provide dumbbell-shaped amphiphilic dendrimers, where the 2,2'-bipyridine cores could be coordinated to FeII centers to afford corresponding metallodendrimers. The ability of the metallic- and non-metallic dendritic structures to self-assemble into functional supramolecular aggregates were furthermore evaluated in aqueous solution. Spherical aggregates with sizes of a few hundred nanometers were generally produced, where controlled disassembly of the metallodendrimers through decomplexation could be achieved.

Recent advances in metallopolymer-based drug delivery systems

Metallopolymers (MPs) or metal-containing polymers have shown great potential as new drug delivery systems (DDSs) due to their unique properties, including universal architectures, composition, properties and surface chemistry. Over the past few decades, the exponential growth of many new classes of MPs that deal with these issues has been demonstrated. This review presents and assesses the recent advances and challenges associated with using MPs as DDSs. Among the most widely used MPs for these purposes, metal complexes based on synthetic and natural polymers, coordination polymers, metal-organic frameworks, and metallodendrimers are distinguished. Particular attention is paid to the stimulus- and multistimuli-responsive metallopolymer-based DDSs. Of considerable interest is the use of MPs for combination therapy and multimodal systems. Finally, the problems and future prospects of using metallopolymer-based DDSs are outlined. The bibliography includes articles published over the past five years.

Exploring the Effect of the Irradiation Time on Photosensitized Dendrimer-Based Nanoaggregates for Potential Applications in Light-Driven Water Photoreduction

Fourth generation polyamidoamine dendrimer (PAMAM, G4) modified with fluorescein units (F) at the periphery and Pt nanoparticles stabilized by L-ascorbate were prepared. These dendrimers modified with hydrophobic fluorescein were used to achieve self-assembling structures, giving rise to the formation of nanoaggregates in water. The photoactive fluorescein units were mainly used as photosensitizer units in the process of the catalytic photoreduction of water propitiated by light. Complementarily, Pt-ascorbate nanoparticles acted as the active sites to generate H2. Importantly, the study of the functional, optical, surface potential and morphological properties of the photosensitized dendrimer aggregates at different irradiation times allowed for insights to be gained into the behavior of these systems. Thus, the resultant photosensitized PAMAM-fluorescein (G4-F) nanoaggregates (NG) were conveniently applied to light-driven water photoreduction along with sodium L-ascorbate and methyl viologen as the sacrificial reagent and electron relay agent, respectively. Notably, these aggregates exhibited appropriate stability and catalytic activity over time for hydrogen production. Additionally, in order to propose a potential use of these types of systems, the in situ generated H2 was able to reduce a certain amount of methylene blue (MB). Finally, theoretical electronic analyses provided insights into the possible excited states of the fluorescein molecules that could intervene in the global mechanism of H2 generation.

Surface Functionalization of Cotton Fabric with Fluorescent Dendrimers, Spectral Characterization, Cytotoxicity, Antimicrobial and Antitumor Activity

Poly(propylenimine) dendrimers from first and third generations modified with 1,8-naphthalimide units and their Zn(II) complexes have been investigated by absorption and fluorescence spectroscopy. These dendrimers have been deposited on a cotton cloth by the extraction method, producing yellow-colored textile materials. They have been characterized by defining their color coordinates L*a*b*, XYZ and xy. The antimicrobial activity of dendrimers has been investigated in vitro against model gram-positive and gram-negative bacteria and yeasts. Being deposited onto the surface of cotton fabric, the studied dendrimers reduced bacterial growth and prevented the formation of bacterial biofilm. Anticancer and cytotoxicity activities have also been performed against HeLa and Lep-3 human tumor cell lines as model systems.

PAMAM dendrimers with a porphyrin core as highly selective binders of Li+ in an alkaline mixture. A spectroscopic study

The selectivity of porphyrin-PAMAM dendrimers toward lithium in an alkaline mixture at the submicromolar levels is promising for sensing applications.