Electroactive Dyes Research Articles

Electroactive Dyes Based on 1,8-Naphthalimide with Acetylene Linkers as Promising OLED Materials - the Relationship Between Structure and Photophysical Properties.

Four A-π-D-π-A type small organic molecules with 1,8-naphthalimide motifs were successfully synthesised. The designed compounds are built of two 1,8-naphthalimide units linked via ethynyl π-linkages with selected functionalised donor motifs i. e. 2,2'-bithiophene, fluorene, phenothiazine and carbazole derivative. The synthesis based on Sonogashira cross-coupling allowed us to obtain the presented dyes with good yields. The resulting symmetrical small molecules' optical, electrochemical and thermal properties were thoroughly investigated, and their potential applicability for the OLED devices was demonstrated. In addition, the relationship between molecular structure and properties was considered by employing experimental and theoretical studies. As a result of using various donor groups, it was possible to achieve efficient electroluminescence in the range from green (DEV4) to orange-red light (DEV3) with a maximum luminance of 3 820 cd/m2 for DEV4. Upon the insertion of an acetylene linker to the designed molecules, the free rotation of D and A fragments, and hence the effective π-electron communication within the entire molecule, is possible, which was confirmed by DFT studies. The obtained dyes are characterised by high thermal stability, reversible oxidation-reduction process, satisfactory optoelectronic properties and good solubility in organic solvents, which is advisable for the application in small molecular organic light-emitting diodes (SM-OLEDs) technology.

Simultaneous detection of exosomal microRNAs by nucleic acid functionalized disposable paper-based sensors

Compared with free microRNAs (miRNAs) in blood, miRNAs in exosomes are more abundant and stable. However, simple, reliable and simultaneous detection of exosomal microRNAs remains a challenging. In this study, we proposed a disposable paper-based electrochemical strategy based on nucleic acid functionalized Zr-MOF, which is label-free and enzyme-free, and could simultaneously detect multiple tumor exosomal miRNAs. We constructed a functionalized metal–organic framework (MOF) with electroactive dyes and capped it with hairpin DNA. This proposed bio-platform and MOF can display different electrochemical signals for different target analyses by changing the structures of dye-loaded and hairpin DNA. In view of this, we skill fully designed two kinds of functional MOFs (Zr/MB and Zr/BG) and used them to simultaneously detect exosomal miRNA-155 and exosomal miRNA-21 (as proof-of-concept analysis). This robust biosensor eliminates multiple time-consuming steps associated with existing miRNAs quantification methods, such as reverse transcription and thermocycler amplification, and achieves molecular-level sensitivity to exosomal miRNA-155 (33.4 aM) and exosomal miRNA-21 (23.1 aM). This study combines the advantages of simultaneous biosensing, which disposable paper-based biosensing strategies and represents an important advance in the field of electrochemical analysis and provides unlimited possibilities for the development of flexible, easy-to-use, and inexpensive bioelectrodes.

Proton-responsive annunciator based on i-motif DNA structure modified metal organic frameworks for ameliorative construction of electrochemical immunosensing interface

Reformative exploitation for metal organic frameworks (MOFs) has been a topic subject in electrochemical sensing, in which the loading of electroactive species is always introduced to enable them to generate electrochemical signal. However, insulation shielding of MOFs and flimsy combination method interfere with the signal readout of electroactive dyes when they are co-immobilized on electrode surface, indicating that an amelioration is imperatively proposed to solve these issues. Herein, a proton-activated annunciator for responsive release of methylene blue (MB) based on i-motif DNA structure modified UIO-66-NH2 was presented to design electrochemical immunosensor (Squamous cell carcinoma antigen was used as the model analyte). With the catalysis of a ZIF-8 immunoprobe contained glucose oxidase (GOx) to glucose in test tube, protons are produced in ambient solution and then they can be used as the key to unlock the i-motif functionalized UIO-66-NH2, releasing the loaded MB molecules to be readout on an improved electrode. This stimuli-responsive mode not merely eliminates the insulation effect of MOFs but also provides a firm loading method for electroactive dyes. Under the optimal conditions, the proposed immunoassay for SCCA had displayed excellent performance with a wide linear range from 1 µg mL−1 to 1 pg mL−1 and an ultralow detection limit of 1.504 fg mL−1 (S/N = 3) under the optimal conditions.

Electrochemical-Based DNA Logic Devices Regulated by the Diffusion and Intercalation of Electroactive Dyes.

Electrochemical-based logic gates are simple to operate, sensitive, controllable, and easy to integrate with silicon-based semiconductor logic devices, showing great application prospects and remaining largely unexplored. Herein, an immobilization-free dual-output electrochemical molecular logic system based on the different diffusivity of electroactive dyes ferrocene (Fc) and methylene blue (MB) toward an indium tin oxide (ITO) electrode under different DNA hybridization reactions was developed. In this system, the hybridization of the catalytic strand IN1 with Fc-modified hairpin DNA H1 triggered an exonuclease III (Exo III) cleavage cycle to obtain free Fc and produce a large number of long double-stranded DNAs via the hybridization chain reaction for intercalating MB, which was previously in the free state. Such a hybridization reaction caused a significant change in the diffusion capacity of MB and Fc toward the ITO electrode, resulting in two electrochemical signals with opposite changes. On this basis, a contrary logic pair library, a parity generator/checker system for differentiating the erroneous bits during data transmission, a parity checker to identify the even/odd natural numbers from 0 to 9, and a series of concatenated logic circuits for meeting the needs of computational complexity were developed. The proposed electrochemical-based molecular logic system greatly expanded the application of the electrochemical method in the construction of logic circuits and provided a conceptual prototype for the development of more advanced and complicated logic devices.

Simultaneous electrochemical determination of nuc and mecA genes for identification of methicillin-resistant Staphylococcus aureus using N-doped porous carbon and DNA-modified MOF.

The detection of Staphylococcus aureus specific gene in combination with the mecA gene is vitally important for accurate identification of methicillin-resistant Staphylococcus aureus (MRSA). A homogeneous electrochemical DNA sensor was fabricated for simultaneous detection of mecA and nuc gene in MRSA. Metal-organic framework (type UiO-66-NH2) was applied as nanocarrier. Two electroactive dyes, methylene blue (MB) and epirubicin (EP), were encapsulated in UiO-66-NH2,respectively, and were locked by the hybrid double-stranded DNA. Based on the target-response electroactive dye release strategy, once target DNA exists, it completely hybridizes with displacement DNA (DEP and DMB). So DEP and DMB is displaced from the MOF surface, causing the release of electroactive dyes. Co-Zn bimetallic zeolitic imidazolate framework-derived N-doped porous carbon serves for electrode modification to improve electrocatalytic performance and sensitivity. The differential pulse voltammetry peak currents of MB and EP were accurately detected at - 0.14V and - 0.53V versus the Ag/AgCl reference electrode, respectively. Under the optimal conditions, the detection limits of mecA gene and nuc gene were 3.7fM and 1.6fM, respectively. Combining the effective application of MOFs and the homogeneous detection strategy, the sensor exhibited satisfactory performance for MRSA identification in real samples. The recovery was 92.6-103%, and the relative standard deviation was less than 5%. Besides, MRSA and SA can also be distinguished. This sensor has great potential in practical applications.

Simple homogeneous electrochemical target-responsive aptasensor based on aptamer bio-gated and porous carbon nanocontainer derived from ZIF-8

A simple homogeneous electrochemical aptasensor was designed by using target-responsive substrate releasing from aptamer-gated zeolitic imidazolate framework-8 (ZIF-8)-derived porous carbon nanocontainer. The nanocontainer (Z-700) was prepared by calcination of ZIF-8 at 700 °C. Z-700 had great biocompatibility, high surface areas and pore volume, especially the graphene-like π-rich structure, which was beneficial for adsorbing aptamer easily. The electroactive dyes methylene blue (MB) was then trapped in the pores of Z-700 and easily capped with aptamer as gatekeeper based on π-stacking interaction. Upon addition of target protein thrombin (Thb), the Thb could specifically recognize and combine with its aptamer to form complex. Thereafter, the aptamer bio-gate opened and the MB released from the pores, which could be detected on the screen-printed electrode. Under the optimized conditions, the proposed Thb aptasensor showed a wide detection range from 1 fM to 1 nM with a low detection limit of 0.57 fM. The strategy by using ZIF-8-derived porous carbon and aptamer bio-gate provides a promising scheme for developing simple, rapid, reliable and ultrasensitive bioassays, which has a great potential as a powerful tool in disease diagnosis and biomedicine.

Nucleic Acid-Functionalized Metal-Organic Framework-Based Homogeneous Electrochemical Biosensor for Simultaneous Detection of Multiple Tumor Biomarkers.

Simultaneous detection of multiple tumor biomarkers is in great demand for early and accurate cancer diagnosis. A homogeneous electrochemical biosensor has been proven to possess high sensitivity, but achieving simultaneous detection of multiple tumor biomarkers is still a challenge. Herein, we develop a novel homogeneous electrochemical biosensor for simultaneous detection of multiple tumor biomarkers based on the functionalized metal-organic frameworks (MOFs). The functionalized MOFs were prepared by using porous UIO-66-NH2 as nanocontainer to load electroactive dyes and dsDNA as a gatekeeper to cap MOFs. In this context, two functionalized MOFs (MB@UIO and TMB@UIO) were fabricated and applied to simultaneous detection of let-7a and miRNA-21, used as the proof-of-concept analytes. The recognition and hybridization of PX with target miRNAs impel the generation of RNA-DNA complexes, which separated from MOFs and allowed the electroactive dyes to be released. In comparison with the case when target miRNAs are absent, two stronger signals are recorded, and dependent on target miRNA concentrations. Thus, simultaneous detection of let-7a and minRNA-21 is achieved, with detection limits down to 3.6 and 8.2 fM, respectively, comparable or lower than those of reported strategies that concentrated on single miRNA detection. Moreover, the proposed biosensor has also been successfully applied for simultaneous detection of target miRNAs spiked in serum samples. Therefore, the proposed strategy was expected to provide more information for early and accurate cancer diagnosis and was an useful application in disease diagnosis and clinical biomedicine.

Diffusivity and intercalation of electroactive dyes-mediated truly ratiometric homogeneous electrochemical strategy for highly sensitive biosensing.

A truly ratiometric homogeneous electrochemical biosensor has been developed for sensitive miRNA detection based on the unique diffusion/intercalation properties of electroactive dyes without the need for electrode modification or materials preparation.

Electro-oxidation of indole-based squaraine dye: A combined in-situ spectroelectrochemical and theoretical study

Indole-based squaraine (ISQ) is a promising group of electroactive dyes that have been widely used as organic photoelectric materials. However, their chemical structure is stable and will cause environmental pollution after being released into nature. Herein, the electrochemical redox chemistry of ISQ and its degradation mechanism on a Pt polycrystalline electrode was investigated. Many results are obtained from voltammograms, electrochemical in-situ UV–Vis and FTIR spectra and quantum chemical calculations: 1) while the potentials were below 1.2 V, ISQ was first oxidized to the radical anion with CO bond formation whereas oxidation shows fully electrochemical irreversibility. 2) an unexpected IR band of CO2 was collected at increasing potentials whereas a new absorption of 420 nm appeared in UV–Vis spectra, suggesting that cleavage of the CC double bond had occurred in the molecular structure of ISQ. 3) The oxidation products of ISQ were 1‑methyl‑3,3‑dimethylndolenium‑2‑one and 3‑oxo‑cyclobut‑1‑enol anion. These findings provide useful information for better understanding the reaction mechanism and designing a suitable treatment strategy for dye pollutants.

An effective electroanalytical approach for the monitoring of electroactive dyes and intermediate products formed in electro-Fenton treatment

Reactive Black 5 (RB5) is an electroactive diazo dye compound derivate of H-acid (coupling reaction), which cannot be effectively degraded by conventional or biological processes. In this work, the feasibility of electro-Fenton (EF) process to treat a simulated effluent polluted by RB5 dye and the effectiveness of electroanalysis by Linear Sweep Voltammetry (LSV) to monitor RB5, intermediates and by-products during the EF treatment have been demonstrated. Several variables on the electrochemical behaviour of RB5 have been determined under EF experimental conditions. The key factors are scan rate and dye concentration (in the presence and the absence of iron) and their effect on shape, position and height of RB5 peaks have been determined to obtain the best sensitivity and selectivity in the voltammetric analysis. Moreover, the iron appears as a strong electrocatalyst that promotes the electron transfer for the oxidation reaction of RB5 on screen-printed carbon electrode, in part, due to a very stable coordinate complex formed with RB5. Besides that, the degradation profiles have revealed the main stages along the EF process and the voltammetric kinetic data has given selective information about the RB5 degradation and the evolution of the electroactive products generated. The formation of aromatic/cyclic organic intermediates, and evolution of carboxylic acids, as well as the inorganic ions released during the treatment were validated by other techniques and a plausible pathway is proposed based on the obtained results.

Electro-optical Properties of Neutral and Radical Ion Thienosquaraines.

Thienosquaraines are an interesting class of electroactive dyes that are useful for applications in organic electronics. Herein, the redox chemistry and electrochromic response of a few newly synthesized thienosquaraines are presented. These properties are compared to those of the commercial 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl]squaraine. The stability of the radical ions formed in electrochemical processes strongly affects these properties, as shown by cyclic voltammetry, in situ spectroelectrochemistry, and quantum chemical calculations. Furthermore, all of the dyes show aggregation tendency resulting in panchromatic absorption covering the whole UV/Vis spectral range.

Large area, soft crystalline thin films of N,N′,N′′-trialkyltriazatriangulenium salts with homeotropic alignment of the discotic cores in a lamellar lattice

N,N′,N′′-Trialkyltriazatriangulenium (R-TATA+) tetrafluoroborate (BF4−) salts form highly ordered thin films directly when spin-cast onto rotating substrates. The homogeneous and crystalline thin films show macroscopic order over centimetres. The crystal structures of the R-TATA·BF4 salts are investigated and compared for the propyl, 3-methylpentyl and octyl derivatives. In all cases the molecules pack in hexagonally ordered bilayers, with segregation of the ionic groups and the alkyl chains. This is a rare packing motif with the rigid discotic TATA+ cores organized co-planarly in sheets separated by perpendicularly oriented alkyl chains, somewhat similar to a crystallized lamellar phase of phospholipid bilayers and the lamellar smectic mesophase of liquid crystals. The structure of the thin films is investigated by optical spectroscopy, X-ray reflectometry and grazing incidence X-ray diffraction. All techniques confirm that the 15–30 nm thick films maintain the lamellar structure of the bulk crystals, are flat on macroscopic length scales, and are completely ordered relative to the substrate. The triazatriangulenium molecules are electroactive dyes, and in the highly anisotropic polycrystalline thin film structure they show intense fluorescence and efficient exciton transport.

A New Approach to Design Light Emitting Devices Using Electroactive Dyes

ABSTRACTOrganic electroluminescence (EL) single layer devices using electroactive dyes incorporated in poly-vinylcarbazole (PVK) were fabricated. The molecular structures of the two-photon dyes are the generic D-π-A;, D-π-D, and A-π-A;, structural motif, composed of a diphenylamine donor (D), a distyrylfluorene π-bridge, and an oxadiazole acceptor (A). A single layer type of EL device of ITO/PVK:DYE/Ca/Al was fabricated. The light emission peak and the threshold of the electroluminescence emission depend on the structure and concentration of the dye. The EL intensity increases with the dye concentration and it was found that as the voltage is increased the brightness increases and reaches a value 498 cd/m2 at an applied voltage of 25 V for the D-π-A; dye. We present a physical explanation of this observed behavior and show that this has significant impact on the design of light emitting devices using these organic dyes.