Electrochemistry and Electrogenerated Chemiluminescence Processes of the Components of Aluminum Quinolate/Triarylamine, and Related Organic Light-Emitting Diodes

Compositional and structural identification of organic matter contributing to high residual soluble aluminum after coagulation

Understanding the complexation of aluminum (Al) with dissolved organic matter (DOM) is of great significance for the control of residual Al in drinking water after treatment. Here, we used high-resolution and accurate mass measurements to identify the composition and structure of DOM contributing to the formation of soluble organically-bound Al during coagulation at near neutral pH (pH 7.50). The results showed that the organic compounds contributing to soluble organically-bound Al were primarily phenolic compounds and aliphatic compounds. Among them, phenolic compounds with a sulfonic acid group could greatly enhance the hydrolysis of polymeric Al and the formation of high concentrations of monomeric/oligomeric Al-DOM complexes. These organic molecules had a mass-to-charge ratio concentrated below 350. Based on the assumption that oxygen-containing functional groups providing unsaturation in the molecular structure were carboxyl groups, it was inferred that the maximum number of carboxyl groups in phenolic compounds and aliphatic compounds was concentrated between 1-2 and 2-4, respectively. The presence of these molecules was responsible for soluble organically-bound Al accounting for over 80 % of the total soluble Al in the supernatant after coagulation in this study. These findings deepen the understanding of the complexation of Al with DOM. In drinking water treatment plants, the combination of coagulation with processes that can remove such characteristic organics is beneficial for controlling residual Al.

CRISPR/Cas12a-Mediated Aptasensor Based on Tris-(8-hydroxyquinoline)aluminum Microcrystals with Crystallization-Induced Enhanced Electrochemiluminescence for Acetamiprid Analysis

Improving the electrochemiluminescence (ECL) efficiency of luminophores has always been the goal of the ECL field. Herein, a novel crystallization-induced enhanced ECL (CIE ECL) strategy was exploited to significantly enhance the ECL efficiency of metal complex tris-(8-hydroxyquinoline)aluminum (Alq₃). Alq₃ monomers self-assembled and directionally grew to form Alq₃ microcrystals (Alq₃ MCs) in the presence of sodium dodecyl sulfate. The highly ordered crystal structure of Alq₃ MCs not only constrained the intramolecular rotation of Alq₃ monomers to decrease nonradiative transition but also accelerated the electron transfer between Alq₃ MCs and coreactant tripropylamine to increase radiative transition, thus leading to a CIE ECL effect. Alq₃ MCs exhibited brilliant anode ECL emission, which was 210-fold stronger than that of Alq₃ monomers. The exceptional CIE ECL performance of Alq₃ MCs coupled the efficient trans-cleavage activity of CRISPR/Cas12a assisted by rolling circle amplification and catalytic hairpin assembly to fabricate a CRISPR/Cas12a-mediated aptasensor for acetamiprid (ACE) detection. The limit of detection was as low as 0.79 fM. This work not only innovatively exploited a CIE ECL strategy to enhance the ECL efficiency of metal complexes but also integrated CRISPR/Cas12a with a dual amplification strategy for the ultrasensitive monitoring of pesticides such as ACE.

Highly efficient electrochemiluminescence labels comprising iridium(iii) complexes

Highly efficient iridium ECL labels exhibiting various emission colors have been developed. Importantly, BSA labeled with the novel iridium labels displays much more intense ECL than the same amount labeled by a traditional ruthenium label in ProCell buffer solution.

π-Stacked poly(vinyl ketone)s with accumulated push–pull triphenylamine moieties in the side chain

Poly(vinyl ketone)s bearing push–pull triphenyamine moiety indicated remarkable absorption hypochromism, reduced redox potentials, and emission red shifts due to a π-stacked conformation.

Self-assembled systems of water soluble metal 8-hydroxyquinolates with surfactants and conjugated polyelectrolytes

We have studied the interaction of 8-hydroxyquinoline-5-sulfonate (8-HQS) with the metal ions Al(iii) and Zn(ii) in aqueous solution in the presence of tetraalkylammonium surfactants using UV/vis absorption, fluorescence, NMR spectroscopy and electrical conductivity measurements, complemented by DFT calculations and molecular dynamics (MD) simulations. Under appropriate conditions, complexes between 8-HQS and metal ions form rapidly, and have similar electronic, spectroscopic and photophysical properties to the corresponding metal quinolates, such as Alq3. These interact with the cationic surfactants, leading to marked increases in fluorescence intensity. However, significant differences are seen in the behavior of the two metal ions. With aluminium, a stable [Al(8-QS)3](3-) anion is formed, and interacts, predominantly through electrostatic interactions, with the surfactant, without disrupting the metal ion coordination sphere. In contrast, with Zn(ii), there is a competition between the metal ion and surfactants in the interaction with 8-HQS, although the [Zn(8-QS)2(H2O)2](2-) species is stable at appropriate pH and surfactant concentration. The studies are extended to systems with the conjugated polyelectrolyte (CPE) poly-(9,9-bis(6-N,N,N-trimethylammonium)hexyl)-fluorene-phenylene bromide (HTMA-PFP), which has a similar alkylammonium chain to the surfactants. Mixing metal salt, 8-HQS and HTMA-PFP in the presence of a nonionic surfactant leads to the formation of a metal complex/CPE supramolecular assembly between the conjugated polyelectrolyte and the metal/8-HQS complex, as demonstrated by electronic energy transfer. The potential of these systems in sensing, light harvesting, and electron injection/transport layers in organic semiconductor devices is discussed.

A structure-property study toward π-extended phosphole chromophores with ambipolar redox properties

We report the synthesis of a series of π-extended dithienophospholes with phenyl or biphenyl terminal groups via Suzuki Miyaura cross-coupling procedures. The incorporation of the dithienophosphole core into the scaffold on oligophenylenes was found to lead to pronounced luminescence properties in solution and the solid state, the latter of which also responded to different solid-state morphologies, i.e., powder versus crystal. More importantly, the investigated molecular architectures also allowed — for the first time — the observation of ambipolar redox behavior of such species, with the biphenyl-extended species in particular showing quasi-reversible reduction and oxidation processes; the observed experimental features were correlated with computational density functional theory studies.

Charge carrier mobility and electronic properties of Al(Op)3: impact of excimer formation

We have studied the electronic properties and the charge carrier mobility of the organic semiconductor tris(1-oxo-1H-phenalen-9-olate)aluminium(III) (Al(Op)3) both experimentally and theoretically. We experimentally estimated the HOMO and LUMO energy levels to be -5.93 and -3.26 eV, respectively, which were close to the corresponding calculated values. Al(Op)3 was successfully evaporated onto quartz substrates and was clearly identified in the absorption spectra of both the solution and the thin film. A structured steady state fluorescence emission was detected in solution, whereas a broad, red-shifted emission was observed in the thin film. This indicates the formation of excimers in the solid state, which is crucial for the transport properties. The incorporation of Al(Op)3 into organic thin film transistors (TFTs) was performed in order to measure the charge carrier mobility. The experimental setup detected no electron mobility, while a hole mobility between 0.6 × 10(-6) and 2.1 × 10(-6) cm(2)·V(-1)·s(-1) was measured. Theoretical simulations, on the other hand, predicted an electron mobility of 9.5 × 10(-6) cm(2)·V(-1)·s(-1) and a hole mobility of 1.4 × 10(-4) cm(2)·V(-1)·s(-1). The theoretical simulation for the hole mobility predicted an approximately one order of magnitude higher hole mobility than was observed in the experiment, which is considered to be in good agreement. The result for the electron mobility was, on the other hand, unexpected, as both the calculated electron mobility and chemical common sense (based on the capability of extended aromatic structures to efficiently accept and delocalize additional electrons) suggest more robust electron charge transport properties. This discrepancy is explained by the excimer formation, whose inclusion in the multiscale simulation workflow is expected to bring the theoretical simulation and experiment into agreement.

The electrochemical catalytic behavior of pyrogallol at an 8-hydroxyquinoline-aluminum complex modified carbon paste electrode and its detection in tomato

Tomato (Solanum lycopersicum) fruit is an excellent food for promoting human health and wellbeing due to its containing polyphenols as antioxidants.

Highly efficient electrochemiluminescence from iridium(iii) complexes with 2-phenylquinoline ligand

Bis-(methylated 2-phenylquinoline) iridium(iii) complexes demonstrated the strongest ECL.

Synthesis, structure, and spectral and electrochemical properties of chromium(iii) tris-(8-hydroxyquinolinate)

Having the HOMO of chromium(iii) tris-(8-hydroxyquinolinate) mainly on metal 3d orbitals and the LUMO on the ligand leads to increased electrochemical stability.

Selective Interlayers and Contacts in Organic Photovoltaic Cells

Organic photovoltaic cells (OPVs) are promising solar electric energy conversion systems with impressive recent optimization of active layers. OPV optimization must now be accompanied by the development of new charge-selective contacts and interlayers. This Perspective considers the role of interface science in energy harvesting using OPVs, looking back at early photoelectrochemical (photogalvanic) energy conversion platforms, which suffered from a lack of charge carrier selectivity. We then examine recent platforms and the fundamental aspects of selective harvesting of holes and electrons at opposite contacts. For blended heterojunction OPVs, contact/interlayer design is especially critical because charge harvesting competes with recombination at these same contacts. New interlayer materials can modify contacts to both control work function and introduce selectivity and chemical compatibility with nonpolar active layers and add thermodynamic and kinetic selectivity to charge harvesting. We briefly discuss the surface and interface science required for the development of new interlayer materials and take a look ahead at the challenges yet to be faced in their optimization.

Long-Term Degradation Mechanism of Organic Light Emitting Devices Based on Small Molecules

The intrinsic degradation of tris(8-hydroxyquinoline) aluminum (AlQ3)-based organic light emitting devices, that leads to the long-term decrease in the electroluminescence efficiency of the devices operated under constant current conditions, is studied. The injection of holes in A1Q3 is found to be the main factor responsible for device degradation. OLEDs with dual HTLs in different arrangements are also presented to demonstrate the proposed degradation mechanism. The role of various approaches to increase OLED lifetime, such as, doping the hole transport layer, introducing a buffer layer at the hole-injecting contact, or using a mixed emitting layer of hole and electron transporting molecules, is explained.

Electronic tuning of ruthenium complexes by 8-quinolate ligands

A series of Ru(II) complexes were synthesized with the deprotonated forms of the ligands 8-hydroxyquinoline (quo(-)) and 5-NO(2)-8-hydroxyquinoline (5-NO(2)-quo(-)) as analogs to the prototypical complex [Ru(bpy)(3)](2+) (bpy = 2,2'-bipyridine). Electrochemistry, spectroscopy and density functional theory calculations were utilized to investigate the electronic tuning of the occupied t(2g)-type orbitals of the metal center with variation in the ligation sphere. The maximum of the lowest energy absorption of complexes containing one, two and three 8-quinolate ligands progressively redshifts from 452 nm in [Ru(bpy)(3)](2+) to 510 nm in [Ru(bpy)(2)(quo)](+), 515 nm in [Ru(bpy)(quo)(2)] and 540 nm in [Ru(quo)(3)](-) in water. This bathochromic shift results from the increase in energy of the occupied t(2g)-type orbital across the series afforded by coordination of each subsequent quo(-) ligand to the Ru(II) center. Time-dependent density functional theory calculations along with electrochemical analysis reveals that the lowest energy transition has contributions in the highest occupied molecular orbital from both the quo(-) ligand and the metal, such that the lowest energy transition is not from an orbital that is purely metal-centered in character as in [Ru(bpy)(3)](2+).

A planar, chip-based, dual-beam refractometer using an integrated organic light-emitting diode (OLED) light source and organic photovoltaic (OPV) detectors

We present a simple chip-based refractometer with a central organic light-emitting diode (OLED) light source and two opposed organic photovoltaic (OPV) detectors on an internal reflection element (IRE) substrate, creating a true dual-beam sensor platform. For first-generation platforms, we demonstrate the use of a single heterojunction OLED based on electroluminescence from an Alq(3)/TPD heterojunction (tris-(8-hydroxyquinoline)aluminum/N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine) and light detection with planar heterojunction pentacene/C(60) OPVs. The sensor utilizes the considerable fraction of emitted light from conventional thin-film OLEDs that is coupled into guided modes in the IRE, instead of into the forward (display) direction. A ray-optics description is used to describe light throughput and efficiency-limiting factors for light coupling from the OLED into the substrate modes, light traversing through the IRE substrate, and light coupling into the OPV detectors. The arrangement of the OLED at the center of the chip provides for two sensing regions: a "sample" channel and a "reference" channel, with detection of light by independent OPV detectors. This configuration allows for normalization of the sensor response against fluctuations in OLED light output, stability, and local fluctuations (temperature) that might influence sensor response. The dual-beam configuration permits significantly enhanced sensitivity to refractive index changes, relative to single-beam protocols, and is easily integrated into a field-portable instrumentation package. Changes in refractive index (DeltaRI) between 10(-2) and 10(-3) RI units could be detected for single beam operation, with sensitivity increased to DeltaRI approximately 10(-4) RI units when the dual-beam configuration is employed.

Metal quinolinolate-fullerene(s) donor-acceptor complexes: evidence for organic LED molecules acting as electron donors in photoinduced electron-transfer reactions

Tris(quinolinolate)aluminum(III) (AlQ3) is the most widely used molecule in organic light-emitting devices. There exists a strong demand for understanding the photochemical and photophysical events originating from this class of molecules. This paper provides the first report on the electron donor ability of MQ(n) (M = Al or Zn for n = 3 or 2) complexes covalently connected to a well-known electron acceptor, fullerene. To accomplish this, fullerene was functionalized with 8-hydroxyquinoline at different ligand positions and their corresponding zinc(II) and aluminum(III) complexes were formed in situ. The weakly fluorescent metal quinolinolate-fullerene complexes formed a new class of donor-acceptor conjugates. The stoichiometry and structure of the newly formed metal quinolinolate-fullerene complexes were established from various spectroscopic methods including matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and computational density functional theory studies. Electrochemical studies involving free-energy calculations suggested the possibility of photoinduced electron transfer from excited metal-quinolinolate complex to the appended fullerene entity. Femtosecond transient absorption studies confirmed such a claim and analysis of the kinetic data allowed us to establish the different photophysical events in sufficient detail. The novel features of this class of donor-acceptor conjugates include faster charge recombination compared to charge separation and decay of the charge-separated state to populate the low-lying fullerene triplet state in competition with direct charge recombination to the ground state.

ESR/DFT study of bis-iminophosphorane cation radicals

Bis-iminophosphoranes containing various types of linkers between two R3P==N moieties were electrochemically oxidized at controlled potential in situ in the electron spin resonance (ESR) cavity. For linkers constituted of phenylenes, conjugated phenylenes or merely a dicyanoethylenic bond, this oxidation led to well-resolved ESR spectra which were characterized by their g values and by their 1H, 14N and 31P isotropic hyperfine constants. These coupling constants agree with those calculated by DFT for the corresponding cation radicals. Experimental and theoretical results clearly indicate that in these species the unpaired electron is mostly delocalized on the bridge and on the nitrogen atoms while the spin density on the phosphorus atoms is particularly small. Cyclic voltammetry and ESR spectra show that the nature of the bridge between the two iminophosphoranes considerably influences the oxidation potential of the compound as well as the stability of the radical cation. Information about the conformation of the precursor containing two Ph3P==N moieties separated by a --C(CN)==C(CN)--group was obtained from its crystal structure.