AIE-Active Fluorene Derivatives for Solution-Processable Nondoped Blue Organic Light-Emitting Devices (OLEDs)

An Intervention into the Diverse Utilities of Fluorenes: A Brobdingnagian Family

The keyword "Fluorene" search in SciFinder found more than 57,000 results, including high-impact journal articles, review articles, patents, books, proceedings, etc. Against this background, a detailed enquiry has been made by our group on various classes of fluorenes and their relevancy. For the past several decades, fluorene and its related compounds have experienced extensive studies, which are attributed to the vast range of applications they possess in various fields like sensors, polymers, OLED devices and even in the pharmaceutical industries. Since fluorene is an important member of the 'polyaromatic-hydrocarbon' family and has proved its relevancy in multidisciplinary areas, summarising those milestones might be worthwhile for future researchers. Here, we intend to highlight the key applications of fluorene derivatives in the form of a review article and have put much effort into consolidating some of their most imperative applications, including those in sensors and medicinal, optoelectronic and electrochemical fields. The manuscript divides the fluorene family into multiple subclasses, counting mono- and polyfluorenes, spirofluorenes, silicon-cored fluorenes, indenofluorenes, etc., based on their structure, and portrays all the critical properties of each class. Since fluorenes are globally accepted as outstanding candidates for numerous applications and practicalities, our effort may find crucial acceptance in the near future.

Threonine-Based Stimuli-Responsive Nanoparticles with Aggregation-Induced Emission-Type Fixed Cores for Detection of Amines in Aqueous Solutions

Stimuli-responsive polymeric nanoparticles (NPs) exhibit reversible changes in the dispersion or aggregation state in response to external stimuli. In this context, we designed and synthesized core-shell NPs with threonine-containing weak polyelectrolyte shells and fluorescent cross-linked cores, which are applicable for the detection of pH changes and amine compounds in aqueous solution. Stable and uniform NP(dTh) and NP(Fl), consisting of fluorescent symmetric diphenyl dithiophene (dTh) and diphenyl fluorene (Fl) cross-linked cores, were prepared by site-selective Suzuki coupling reactions in self-assembled block copolymer. NP(Fl) with the Fl unit in the core showed a high fluorescence intensity in different solvents, which is regarded as an aggregation-induced emission-type NP showing strong emission in aggregated states in the cross-linked core. Unimodal NPs were observed in water at different pH values, and the diameter of NP(Fl) changed from 122 (pH = 2) to 220 nm (pH = 11). Furthermore, pH-dependent changes of the fluorescence peak positions and intensities were detected, which may be due to the core aggregation derived from the deprotonation of the threonine-based shell fragment. Specific interactions between the threonine-based shell of NP(Fl) and amine compounds (triethylamine and p-phenylenediamine) resulted in fluorescence quenching, suggesting the feasibility of fluorescent amine detection.

Blue organic light-emitting diodes with hybridized local and charge-transfer excited state realizing high external quantum efficiency

Donor-spacer-acceptor (D-π-A) materials CAPI and CCAPI, with hybridized local and charge transfer (HLCT) emissive states, have been synthesized. The twisting D-π-A architecture promotes the partial separation of HOMO and LUMO, leading to an enhanced % CT component, and the anthracene moiety in CAPI and CCAPI increases the conjugation length, leading to an enhanced % LE component. The non-doped device with CCAPIb shows the blue emission (450 nm) with maximum current efficiency (η c), power efficiency (η p), and external quantum efficiency (η ex) of 16.83 cd A-1, 15.32 lm W-1, and 12.0%, respectively, as well as exciton utilization efficiency (EUE) of 95% with a luminance of 32 546 cd m-2 and a roll-off efficiency of 0.53%. The new design strategy has great potential for developing high-performance blue electroluminescent materials.

Highly fluorescent aryl-cyclopentadienyl ligands and their tetra-nuclear mixed metallic potassium-dysprosium clusters

Two alkyl substituted triaryl-cyclopentadienyl ligands [4,4′-(4-phenylcyclopenta-1,3-diene-1,2-diyl)bis(methylbenzene) (1) and 4,4′,4′′-(cyclopenta-1,3-diene-1,2,4-triyl)tris(methylbenzene) (2)] have been synthesized via cross-aldol condensation followed by Zn-dust mediated cyclization and acid catalyzed dehydration reactions. The fluorescence properties of 1 and 2 have been studied in solution and solid state. The ligands exhibited aggregation-induced emission enhancement (AIEE) in THF/water solution. 1 and 2 have been found to be significantly more fluorescent in the solid state than in their respective solutions. This phenomenon can be attributed to the strong intermolecular CH⋯π interactions present in 1 and 2 which leads to the tight packing of molecules in their solid-state. Both 1, 2 and their corresponding anions have been studied by theoretical calculations. Ligands 1 and 2 have been shown to react with anhydrous DyCl₃ in the presence of potassium metal at high temperature to afford two fluorescent chloride-bridged tetra-nuclear mixed potassium–dysprosium metallocenes [(Me₂Cp)₄Dy₂^IIICl₄K₂]·3.5(C₇H₈) (5) and [(Me₃Cp)₄Dy₂^IIICl₄K₂]·3(C₇H₈) (6), respectively in good yields.

Alkyl substituted triaryl-cyclopentadienyl ligands with aggregation-induced emission enhancement (AIEE) properties and their applications in the syntheses of novel chloride bridged tetra-nuclear mixed potassium–dysprosium metallocenes.

A Facile Approach towards Fluorescent Nanogels with AIE-Active Spacers

A facile and efficient approach for design and synthesis of organic fluorescent nanogels has been developed by using a pre-synthesized polymeric precursor. This strategy is achieved by two key steps: (i) precise synthesis of core⁻shell star-shaped block copolymers with crosslinkable AIEgen-precursor (AIEgen: aggregation induced emission luminogen) as pending groups on the inner blocks; (ii) gelation of the inner blocks by coupling the AIEgen-precursor moieties to generate AIE-active spacers, and thus, fluorescent nanogel. By using this strategy, a series of star-shaped block copolymers with benzophenone groups pending on the inner blocks were synthesized by grafting from a hexafunctional initiator through atom transfer radical copolymerization (ATRP) of 4-benzoylphenyl methacrylate (BPMA) or 2-(4-benzoylphenoxy)ethyl methacrylate (BPOEMA) with methyl methacrylate (MMA) and tert-butyldimethylsilyl-protected 2-hydroxyethyl methacrylate (ProHEMA) followed by a sequential ATRP to grow PMMA or PProHEMA. The pendent benzophenone groups were coupled by McMurry reaction to generate tetraphenylethylene (TPE) groups which served as AIE-active spacers, affording a fluorescent nanogel. The nanogel showed strong emission not only at aggregated state but also in dilute solution due to the strongly restricted inter- and intramolecular movement of TPE moiety in the crosslinked polymeric network. The nanogel has been used as a fluorescent macromolecular additive to fabricate fluorescent film.

Synthesis and properties of dicarbazolyltriphenylethylene-substituted fluorene derivatives exhibiting aggregation-induced emission enhancement

Two novel dicarbazolyltriphenylethylene-substituted fluorene derivatives DctF and Dct 2 F were synthesized by the Wittig-Horner and Suzuki coupling reactions. It was reasoned that introducing linear alkyl chains into the fluorene structure could facilitate the deposition of high-quality films by an economical and simple process. The thin solid films of DctF and Dct 2 F show strongly enhanced emissions in comparison to their dilute solutions, which indicate the aggregation-induced emission enhancement (AIEE). Their decomposition temperatures (T d) exceed 400°C and the glass transition temperature (T g) of DctF is 105°C. The maximum fluorescence emission wavelengths are in the region of 458–469 nm.