High Solid-state Fluorescence Research Articles

Novel triphenylamine-pyrene-based AIEgens: Specific detection and imaging of H2O2 in aqueous solution and cells

H2O2 plays a key regulatory role as a bioendogenous reactive oxygen species in cells and organisms. However, excessive production or accumulation of H2O2 during mitochondrial oxidative stress may lead to oxidative damage of cellular proteins and trigger rheumatic diseases, cancers, and a variety of neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. In addition, H2O2 is a very useful chemical widely employed in the textile and chemical industries, and its excessive emission not only pollutes the environment but also jeopardizes human health. Therefore, the sensitive and specific detection and removal of H2O2 is important for early diagnosis of diseases, treatment prognosis and environmental pollution monitoring. We have designed two novel triphenylamine-based AIEgens MOTPP and MOTPP-B, which each have a high solid-state fluorescence quantum yield and excellent aggregation-induced emission properties. MOTPP-B has high selectivity and anti-interference ability toward H2O2, a wide pH tolerance range, a sensing process that is complete in under 40 min, and a low detection limit of 120.77 nM. It has been successfully applied for the detection of low concentrations of H2O2 in the environment and to dual-channel imaging of low concentrations of exogenous H2O2 in living cells.

Impact of the phenyl on fluorescence properties of cyanostilbene modified tetraphenylethene compounds

Two novel cyanostilbene-modified tetraphenylethene derivatives were constructed by Williamson etherification, Suzuki coupling and Knoevenagel condensation reactions. Both compounds exhibited aggregation-induced emission and strong solid-state fluorescence behaviors with extremely high fluorescence quantum yield due to the distorted molecular conformation. Strangely, the compound without additional phenyl spacer did not show mechanochromic behavior, whereas, the compound with an additional phenyl spacer exhibited distinct mechanochromic behavior with the red-shifted emission wavelength from 480 nm to 503 nm upon grinding. The distinct differences in mechanochromic behaviors between the reported compounds could be attributed to that the additional phenyl spacer had benefits for the molecular planarization with external mechanical force. This investigation provided a method to construct mechanochromic material with aggregation-induced emission behavior and high solid-state fluorescence quantum yield and promoted the utilization in rewritable luminescent paper.

Anion-directed cationic supramolecular dyes with reversible mechanochromism and fabric staining

It is vital to create supramolecular dyes with excellent photo-luminescence properties based on host-gust interaction. In this study, we present three novel self-assembled cationic supramolecular dyes driven by host-guest electrostatic interaction and with ultrasmall cavities. These cationic dyes were developed and synthesized using pyridine-substituted phenanthrene, triphenylamine (TPA), and tetraphenyl ethylene (TPE) as chromophores through the pyridine quaternary ammonium salt reaction. These anion-trapped supramolecular dyes exhibit outstanding aggregation-induced emission (AIE) characteristics as well as reversible mechanochromism behavior and high solid-state fluorescence quantum yields (∼60.87 %). Furthermore, the cationic supramolecular dyes directly stain cotton fibers with 50 % dyeing rate in water-methanol solutions, in which the deprotonated glucose-O- guest possibly interacts with the cationic dye through host-guest encapsulation. Additionally, we characterized the dyeing process through IR spectroscopy, UV–vis spectroscopy, fluorescence spectroscopy, and energy-dispersive X-ray spectroscopy (EDS). Due to the reversible, tractable, and high-contrast mechanochromism of the dyes, they can make up a color-changing flower pattern. Thus, we anticipate that these dyes will have potential applications in information security storage and anti-counterfeiting.

Mechanochromic luminescence from N,O-Chelated diphenylborinates

A series of N,O-bidentated BPh2 complexes (B1–B3) have been designed and synthesized through the direct reaction of N,O-chelate ligands and diaryl borate solutions. Their crystal structures, photophysical and mechanochromic properties were systematically studied. As verified by both experimental and calculated results, all these compounds possess inherent D-A structures, and adopt highly distorted molecular conformations. Multiple weak intermolecular interactions and relatively loose packing are prevailing in their crystal structures. These favorable structure features promise high solid-state fluorescence efficiency and high color contrast reversible mechanochromic for the three dyes. Moreover, their photophysical and mechanical responsive properties have been found structurally dependent, which are mainly modulated by electronic and steric effects derived from different substitutions in the ligand and the boron atom. As a result, B2 with the most twisted and loosely packed structure shows a most sensitive and pronounced mechanochromic response. Our study thus shows that selection of a N,O-bidentated BPh2 based emitter enables the development of excellent MCL-active materials. The current design strategy will be beneficial for the facile access to various advanced BPh2 based dyes for promising applications in optical force sensors, optoelectronic devices and so on.

Self-absorption-free excited-state intramolecular proton transfer (ESIPT) emitters for high brightness and luminous efficiency organic fluorescent electroluminescent devices

ESIPT derivatives functionalized with N-electron donating moieties show pure keto form emissions with high solid-state fluorescence. As emitters, their OLEDs exhibit exceptionally high brightness (41 292–44 820 cd m−2) and high luminous efficiency (8.41–10.30 cd A−1).

Configuration-controllable synthesis of Z/E isomers based on o-carborane-functionalized tetraphenylethene

Two Z/E isomers, namely, Z-TPE-2Car and E-TPE-2Car, with clear configuration were synthesized using an effective route and have high solid-state fluorescence quantum yields, reaching 99% and 90%, respectively.

Dual responsive cellulose microspheres with high solid-state fluorescence emission

Materials that respond to multiple stimuli such as magnetic field and light are attractive for security and medical diagnostic applications. One of the major challenges in dual functional microspheres is that the presence of magnetic nanoparticles can quench fluorescence emission. Also, there is a probability of solid-state quenching due to the proximity of the fluorophore. We report here a facile approach to prepare cellulose microspheres with high solid-state fluorescence using 40 % tetrabutylammonium hydroxide (TBAH). The fluorescence quenching effect due to the presence of Fe3O4 nanoparticles and solid-state quenching due to aggregation of fluorophore was systematically investigated. Microspheres with the detectable magnetic response and fluorescence quantum yield as high as 0.57 (FMB 414) was obtained by optimizing the reaction conditions. Such a high quantum yield has not been reported before for dual stimuli-responsive fluorescent microspheres. The magnetic and fluorescent properties were found to be durable even after multiple washing cycles. These dual responsive cellulose microspheres can be added as security features to authenticate documents such as passports, degree certificates, currency notes, financial documents etc.

Remarkable mechanofluorochromism and low efficiency-off electroluminescence from a fully aromatic D-A cruciform emitter

Two-dimensional aryl center-crossed cruciforms generally exhibit the strongly twisted conformation and the spatial separation of frontier molecular orbitals, which can render the emitters destructible packing structures and high solid-state fluorescence efficiency. In the current work, we design and synthesize a benzene-centered cruciform emitter (DOT) with two adjacent phenyloxadiazoles and two adjacent triphenylamines starting from commercially available chemicals. Single crystal analysis indicates that DOT molecules loosely pack together in a twisted conformation and weak inter-molecular interactions. Upon mechanical grinding, the crystalline DOT is changed into an amorphous state, accompanying with a remarkable (56 nm) mechanofluorochromism (MFC). In view of the crossed donor and acceptor structure and the strong solid-state fluorescence, the non-doped electroluminescence (EL) devices with the structures ITO/HATCN/NPB or TAPC/DOT/TPBi/LiF/Al are fabricated. The devices efficiently emit 500 nm green EL with the low turn on voltage of 2.7 V and the low efficiency roll-off. Thus, we have provided a feasible synthetic strategy for various isomers and analogues of fully aromatic benzene-centered D‒A cruciforms and demonstrated a new class of candidates for MFC and EL materials.

Quantitative and rapid detection of explosives using an efficient luminogen with aggregation-induced emission characteristics

The development of fluorescent sensors for explosive detection with high sensitivity is of great importance for antiterrorism and environmental protection. A new efficient AIE luminogen, abbreviated as TPE-SFX, is designed and synthesized. It enjoys typical AIE features and high solid-state fluorescence quantum yield. It can be fabricated into fluorescent dots for explosive detection with good selectivity and rapid response. The fluorescence quenching process and mechanism are investigated. Taking advantage of its high solid-state fluorescence efficiency, TPE-SFX is further utilized on filter paper as solid-state sensor. Through analysis of grayscale variation of fluorescence images, a simple and reliable method is developed for quantitative analysis of picric acid (PA) with a low detection limit to 0.12 nmol/cm2. It is the first report of efficient luminogen utilized on filter paper for quantitative analysis of explosives with high sensitivity. Moreover, the fluorescent filter paper can be regenerated through an environmentally benign method simply by washing with water. In addition, the fluorescent filter paper enjoys good thermal stability, which can endure a high temperature up to 100 °C. These good results will shed some light on the development of quantitative, sensitive, and portable devices for in situ explosive detection in the environment.

Synthesis, aggregation-induced emission (AIE) and electroluminescence of carbazole-benzoyl substituted tetraphenylethylene derivatives

Aggregation-induced emission (AIE) materials offer a solution to obtain high fluorescence efficiencies in solid state which is desirable for optoelectronic devices and display. Here in this work, three new types of D-π-A-π-D AIE luminogens based on carbazole-benzoyl substituted tetraphenylethylene (TPE) derivatives were designed and successfully synthesized. Meanwhile, their photophysical properties as well as electroluminescence (EL) characteristics were studied. These luminogens show good AIE property with high solid-state fluorescence quantum yields. Furthermore, the emission wavelengths for these three luminogens, both in solutions and in solid state, exhibit negligible variation by increasing the number of donor group. All three luminogens show solvatochromism and negative solvatokinetic effect in different solvents. More interesting is that on increasing number of donor groups, their thermal and morphological stability present regular change by increasing the number of carbazole-benzoyl group. The performance of non-doped OLED device based on TPE-3BZ-Cz is superior than the other two luminogens, which has been proved by further electroluminescence evaluation.

Red/NIR-Emissive Benzo[d]imidazole-Cored AIEgens: Facile Molecular Design for Wavelength Extending and In Vivo Tumor Metabolic Imaging.

Aggregation-induced emission (AIE) luminogens (AIEgens) with red/near-infrared (NIR) emissions are appealing for applications in optoelectronics and biomedical engineering owing to their intrinsic advantages of efficient solid-state emission, low background, and deep tissue penetration. In this context, an AIEgen with long-wavelength emission is synthesized by introducing tetraphenylethene (TPE) to the periphery of electron-deficient spiro-benzo[d]imidazole-2,1'-cyclohexane (BI). The resulting AIEgen, abbreviated as 2TPE-BI, adopts a donor-acceptor structure and shows bathochromic absorption and emission with a larger Stokes shift of 157 nm in acetonitrile than that based on benzo[c][1,2,5]thiadiazole. It also exhibits a high solid-state fluorescence quantum yield of 56.6%. By further insertion of thiophene to its molecular structure generates 2TPE-2T-BI with higher conjugation and NIR emission. 2TPE-2T-BI can be fabricated into AIE dots for in vivo metabolic labeling through bio-orthogonal click chemistry. These results open a new approach for facile construction of long-wavelength emissive AIEgens based on the BI core.

Benzo[4,5]thiazolo[3,2- c][1,3,5,2]oxadiazaborinines: Synthesis, Structural, and Photophysical Properties.

A family of highly emissive benzo[4,5]thiazolo[3,2- c][1,3,5,2]oxadiazaborinines, conjugated with the donor 4-dimethylaminophenyl group, was designed and synthesized. Their photophysical, both in solution and in the solid state, and structural properties were investigated. The influence of donor and acceptor substituents (R) in the benzothiazole unit on photophysical properties of complexes was found out. The tetrafluorobenzothiazole analogue exhibits nonbonded nuclear spin-spin coupling between fluorines from the BF2 group and α-fluorine atom at the benzene ring. Additionally, this boron complex demonstrates a comparatively high solid-state fluorescence quantum yield (Φ = 0.34).

Highly stable and fast blue color/fluorescence dual-switching polymer realized through the introduction of ether linkage between tetraphenylethylene and triphenylamine units

A novel electroactive/AIE-active polymer with tetraphenylethylene (TPE) and triphenylamine (TPA) units was prepared from a newly synthesized diamine, 4-tetraphenylethyleneoxy-4′,4″-diaminotriphenylamine, and cyclohexanedicarboxylic acid. By ingenious introduction of ether linkage between TPE and TPA units, the obtained polymer simultaneously exhibited high solid-state fluorescence, colorless neutral state, excellent electrochemistry stability, rapid responsive rate and long-term blue (one of the three primary colors) electrochromic/electrofluorochromic dual-switching, demonstrating great potential in optoelectronic applications.

Specific Two-Photon Imaging of Live Cellular and Deep-Tissue Lipid Droplets by Lipophilic AIEgens at Ultralow Concentration

Lipid droplets are highly associated with obesity, diabetes, inflammatory disorders, and cancer. A reliable two-photon dye for specific lipid droplets imaging in live cells and live tissues at ultralow concentration has rarely been reported. In this work, four new aggregation-induced emission luminogens (AIEgens) based on the naphthalene core were designed and synthesized for specific two-photon lipid droplet staining. The new molecules, namely, NAP AIEgens, exhibit large Stokes shift (>110 nm), high solid-state fluorescence quantum yield (up to 30%), good two-photon absorption cross section (45–100 GM at 860 nm), high biocompatibility, and good photostability. They could specifically stain lipid droplets at ultralow concentration (50 nM) in a short time of 15 min. Such ultralow concentration is the lowest value for lipid droplets staining in live cells reported so far. In vitro and ex vivo two-photon imaging of lipid droplets in live cells and live mice liver tissues were successfully demonstrated. In ad...

Synthesis, aggregation-induced emission and electroluminescence of new luminogens based on thieno[3,2-b]thiophene S,S-dioxide

Organic luminescent materials with high fluorescence efficiencies in the solid state are highly desired in OLED devices. In this work, we report the synthesis and characterization of a series of novel dipolar luminogens based on thieno [3,2-b]thiophene S,S-dioxide (TTDO). The crystal structures, photophysical property, thermal stability, electronic structures and electrochemical behaviors of these TTDO-based luminogens are investigated. These luminogens have good aggregation-induced emission (AIE) property with high solid-state fluorescence quantum yields, and their emission wavelengths are tuned from green to red by different electron-donating substituents. They enjoy high thermal and morphological stabilities and have low LUMO energy levels. Nondoped OLEDs are fabricated with these new luminogens, providing orange to red electroluminescence (568–610 nm) with maximum external quantum efficiencies of up to 2.79%. These results demonstrate that these new AIE-active luminogens could be promising candidates for OLEDs.

AIE-Active Polyamide Containing Diphenylamine-TPE Moiety with Superior Electrofluorochromic Performance.

Electrofluorochromism has attracted great attention due to the intelligence optoelectronic and sensing applications. The intrinsically switchable fluorophores with high solid-state fluorescence are regarded as key for ideal electrofluorochromic materials. Here, we reported an AIE-active polyamide with diphenylamine and tetraphenylethylene units, showing high fluorescence quantum yield up to 69.1% for the solid polymer film and stable electrochemical cycling stability. The polyamide exhibited reversible color and emission switching even in hundreds of cycles, and the fluorescence on/off contrast ratio was determined up to 417, which is the highest value to our knowledge. Furthermore, as the response time is vital for the real-life applications, to speed up the response of electrofluorochromism, a porous polymer film was readily prepared through a facile method, notably exhibiting high fluorescence contrast, long-term stability and obviously improved response, due to the sharply increased surface area. Therefore, the AIE-functionalization combining the porous structure strategy will synergistically and dramatically improve the electrofluorochromic performance, which will also promote their practical applications in the near future.

Thermally Stable and Highly Luminescent Green Emissive Fluorophores with Acenaphtho[1,2‐k]fluoranthene Cores and Aromatic Amine Groups

Four acenaphtho[1,2-k]fluoranthene-cored fluorophores 1-4 attached by a variety of N-containing electron-donating groups have been designed and synthesized. The appending N-containing moieties and the central acenaphtho[1,2-k]fluoranthene core form twisted molecular configurations and lead to separated HOMO and LUMO frontier molecular orbitals. X-ray crystallographic analysis demonstrates that the substituted aromatic amines separate the luminescent π-conjugated cores in the solid state. These compounds display excellent thermal and amorphous stabilities, high solid-state fluorescence quantum efficiencies, and ambipolar charge transporting properties, indicating that they are ideal candidates for fabricating non-doped organic light-emitting diodes (OLEDs). The device based on compound 4 exhibits the best electroluminescent performance with an external efficiency of 2.82 % and brightness of 45800 cd m-2 , demonstrating the potential applications of this compound for OLED displays and lighting.

Branched truxene and triindole compounds and their solid-state luminescent enhancement

C3-symmetric truxene and triindole have been widely used to design the branched optoelectronic molecules. However, most of them exhibit high luminous efficiency in the solution and quenched luminescence in the solid state. Here, we respectively chose alkylated truxene and triindole as the central core, 2-methylphenyl as the peripheral functional groups to synthesize three branched compounds. Their photophysical properties have been explored combining with the theoretical calculation. The three compounds exhibit good solubility and high solid-state fluorescence quantum yields. The absorption and emission peaks of triindole compound exhibit apparent red-shift in comparison with those of truxene compounds, which indicates triindole more highly electron delocalization than truxene. The single-crystal structure shows that alkylation of the central core and branched steric bulkiness of these molecules effectively reduce the intermolecular π⋯π stacking and avoid the non-radiative transition of these molecules from excited state to ground state in the solid state.

9-Arylvinyl- and 9,10-bis(arylvinyl)-anthracenes with phenyl and naphthyl as aryl moieties: Differential aggregation behaviors and optoelectronic properties

In this paper, we have synthesized our simple twisting arylvinyl anthracene derivatives, 9-styrylanthracene (ASB), 9,10-bis(styryl)anthracene (SB), 9-(2-(naph- thalen-1-yl)vinyl)anthracene (ASN) and 9,10-bis((naphthalen-1-yl)vinyl)anthracene (SN), to demonstrate the effect of skeleton symmetry on optical and optoelectronic properties. The results showed that SB and SN are weak emission with the fluorescence quantum yields (Φ) of ca. 7% but ASB and ASN are highly fluorescent (Φ≈50%) in THF solution, although they all exhibit high solid-state fluorescence efficiencies (22~50%). Grinding could induce about 20nm of spectral shift of ASB and ASN crystalline fluorescence, but SB and SN crystals hardly exhibit mechano- fluorochromic behavior. Furthermore, the evaporated films of SB and SN are fragile due to re-crystallization soon, but those of ASB and ASN are stable and could be used as the bulk emissive layer exhibiting commendable electroluminescent performances. This finding indicates that the geometric structures of conjugated skeletons could influence the electronic and aggregate structure of organic luminogens, and then alter their optical and optoelectronic properties.

Synthesis and High Solid-State Fluorescence of Cyclic Silole Derivatives

Cyclotetrasiloxanes 1–3 containing different silole-based fluorogenic units (silafluorene, 1,3-diphenyl-9-silafluorene, tetraphenylsilole) were synthesized by cohydrolysis and condensation reactions. Their optical properties in solution and as crystals were studied. These compounds have low quantum yields in solution (Φfl = 0.01–0.18) with fluorescence maxima at 359–375 nm for silafluorene-containing compounds 1 and 3 and at 491 nm for AEE-active tetraphenylsilole compound 2. However, 1–3 have high solid-state quantum yields (Φfl = 0.65–0.78) with fluorescence maxima at 377–390 nm for compounds 1 and 3 and at 517 nm for tetraphenylsilole- and silafluorene-containing compound 2. Packing analysis of 1–3 in the crystal structure and MO and excited-state calculations were performed to explore possible fluorescence mechanisms in these compounds.