Achieving Order in Disorder: Stabilizing Red Light-Emitting α-Phase Formamidinium Lead Iodide.

While formamidinium lead iodide (FAPbI3) halide perovskite (HP) exhibits improved thermal stability and a wide band gap, its practical applicability is chained due to its room temperature phase transition from pure black (α-phase) to a non-perovskite yellow (δ-phase) when exposed to humidity. This phase transition is due to the fragile ionic bonding between the cationic and anionic parts of HPs during their formation. Herein, we report the synthesis of water-stable, red-light-emitting α-phase FAPbI3 nanocrystals (NCs) using five different amines to overcome these intrinsic phase instabilities. The structural, morphological, and electronic characterization were obtained using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), and X-ray photoelectron spectroscopy (XPS), respectively. The photoluminescence (PL) emission and single-particle imaging bear the signature of dual emission in several amines, indicating a self-trapped excited state. Our simple strategy to stabilize the α-phase using various amine interfacial interactions could provide a better understanding and pave the way for a novel approach for the stabilization of perovskites for prolonged durations and their multifunctional applications.

Nitrogen-Doped CuO@CuS Core-Shell Structure for Highly Efficient Catalytic OER Application.

Water electrolysis is a highly efficient route to produce ideally clean H2 fuel with excellent energy conversion efficiency and high gravimetric energy density, without producing carbon traces, unlike steam methane reforming, and it resolves the issues of environmental contamination via replacing the conventional fossil fuel. Particular importance lies in the advancement of highly effective non-precious catalysts for the oxygen evolution reaction (OER). The electrocatalytic activity of an active catalyst mainly depends on the material conductivity, accessible catalytically active sites, and intrinsic OER reaction kinetics, which can be tuned via introducing N heteroatoms in the catalyst structure. Herein, the efficacious nitrogenation of CuS was accomplished, synthesized using a hydrothermal procedure, and characterized for its electrocatalytic activity towards OER. The nitrogen-doped CuO@CuS (N,CuO@CuS) electrocatalyst exhibited superior OER activity compared to pristine CuS (268 and 602 mV), achieving a low overpotential of 240 and 392 mV at a current density of 10 and 100 mA/cm2, respectively, ascribed to the favorable electronic structural modification triggered by nitrogen incorporation. The N,CuO@CuS also exhibits excellent endurance under varied current rates and a static potential response over 25 h with stability measured at 10 and 100 mA/cm2.

Solid-State Synthesis and Optical Studies of Water-Stable Pb2+-Doped Mn2+ Complexes.

The limited Mn2+ doping that occurs in lead halide perovskites has been widely described, while the Pb2+ doping that occurs in Mn2+ halide perovskites has not been studied well. Generally, a large amount of doping of Mn2+ in lead halide perovskite degrades the perovskite structure; eventually, high orange luminescence of Mn2+ dopant has not been achieved. In our present study, we followed a reverse strategy, i.e., Pb2+ doping in Mn2+ halide perovskites, to increase the amount of Mn2+ in halide perovskites through the high-energy ball milling method. This strategy yields bright-fluorescence orange light-emitting Mn2+-doped perovskite with a Mn/Pb ratio of 95%, which is the highest among Mn2+-doped perovskites. Zero-dimensional (0D) Mn2+ perovskites and two-dimensional (2D) Pb2+-doped Mn2+-based perovskites were successfully synthesized and characterized. During the mechanochemical engineering, Pb2+ ions partially occupy the site of Mn2+ ions and act as a luminescence activator. Mn2+-based 2D perovskites with the proper amounts of Pb2+ ions as dopant ions and phenylethylammonium (PEA+) as dielectric organic cations show enhanced stability in water. The dual-emissive properties of these 2D-Pb2+-doped Mn2+-based perovskites were also investigated by using single-particle imaging fluorescence. We believe that these findings will pave the way for designing eco-friendly dimension and bandgap tunable layered perovskites.

Polymer Backbone Stabilized Methylammonium Lead Bromide Perovskite Nano Islands.

Organic-inorganic hybrid perovskite materials continue to attract significant interest due to their optoelectronic application. However, the degradation phenomenon associated with hybrid structures remains a challenging aspect of commercialization. To overcome the stability issue, we have assembled the methylammonium lead bromide nano islands (MNIs) on the backbone of poly-3-dodecyl-thiophene (PDT) for the first time. The structural and morphological properties of the MNI-PDT composite were confirmed with the aid of X-ray diffraction (XRD) studies, Field emission scanning electron microscope (FESEM), and X-ray photoelectron spectroscopy (XPS). The optical properties, namely absorption studies, were carried out by ultraviolet-visible spectroscopy. The fluorescent behavior is determined by photoluminescence (PL) spectroscopy. The emission peak for the MNI-PDT was observed at 536 nm. The morphology studies supported by FESEM indicated that the nano islands are completely covered on the surface of the polymer backbone, making the hybrid (MNI-PDT) stable under environmental conditions for three months. The interfacial interaction strategy developed in the present work will provide a new approach for the stabilization of hybrids for a longer time duration.

Recent update on the electroactive oligopyrrolic macrocyclic hosts with a Bucky-ball heart.

Supramolecular chemistry is a multidisciplinary research area mostly associated with the investigation of host-guest interactions within intricate three-dimensional (3D) molecular architectures held together reversibly by various non-covalent interactions. Continuous efforts to develop such kinds of complex host-guest systems with designer oligopyrrolic macrocyclic receptors are a rapidly growing research domain, which is deeply involved in applied supramolecular chemistry research. These host-guest supramolecular complexes can be constructed by combining suitable electron-rich oligopyrrolic donors (as a host) with complementary electron-poor guests (as acceptors), held together by the ionic force of attraction triggered by intermolecular charge/electron transfer (CT/ET) transitions. Some of these resulting CT/ET ensembles are potential candidates for the construction of efficient optoelectronic materials, optical sensors, molecular switches, etc. In this Feature Article we aim to focus on these supramolecular ensembles composed by size and shape complementary electroactive oligopyrrolic molecular containers, which are suitable for spherical guest (e.g., buckminsterfullerene) complexation. We also provide a "state-of-the-art" overview on plausible applications of these particular host-guest systems. Our aim is to cover only specific electron-rich tetrathiafulvalene (TTF)-based oligopyrrolic receptors, e.g., TTF-calix[4]pyrroles, TTF-cryptands, TTF-porphyrins and exTTF-porphyrin-based molecular motifs reported to date, along with a brief outlining of their "functional behaviour" in materials chemistry research.

Microstructure and Oxygen Evolution Property of Prussian Blue Analogs Prepared by Mechanical Grinding.

Solvent-free mechanochemical synthesis of efficient and low-cost double perovskite (DP), like a cage of Prussian blue (PB) and PB analogs (PBAs), is a promising approach for different applications such as chemical sensing, energy storage, and conversion. Although the solvent-free mechanochemical grinding approach has been extensively used to create halide-based perovskites, no such reports have been made for cyanide-based double perovskites. Herein, an innovative solvent-free mechanochemical synthetic strategy is demonstrated for synthesizing Fe4[Fe(CN)6]3, Co3[Fe(CN)6]2, and Ni2[Fe(CN)6], where defect sites such as carbon-nitrogen vacancies are inherently introduced during the synthesis. Among all the synthesized PB analogs, the Ni analog manifests a considerable electrocatalytic oxygen evolution reaction (OER) with a low overpotential of 288 mV to obtain the current benchmark density of 20 mA cm-2. We hypothesize that incorporating defects, such as carbon-nitrogen vacancies, and synergistic effects contribute to high catalytic activity. Our findings pave the way for an easy and inexpensive large-scale production of earth-abundant non-toxic electrocatalysts with vacancy-mediated defects for oxygen evolution reaction.

Recent progress in the stabilization of low band-gap black-phase iodide perovskite solar cells.

All-inorganic and organic-inorganic hybrid perovskite solar cells (PSCs) have taken a quantum leap owing to their high performance and low-cost solution processability. Their efficiency has been dramatically increased up to ∼26%, matching the conventional inorganic photovoltaics like monocrystalline Si (26.1%), polycrystalline Si (21.6%), CdTe (22.1%), and CIGS (22.3%). Such outstanding performance has been achieved due to their excellent optoelectronic properties, such as a direct bandgap in the visible region, a very high absorption coefficient, a long charge-carrier diffusion length, and ambipolar carrier transport characteristics. FAPbI3 (FA = formamidinium) and CsPbI3 perovskites among the pool of perovskites are recommended for solar cell applications because they meet all the requirements for photovoltaic applications. However, the fundamental problem of these perovskites is that their photoactive black phase is highly unstable under ambient conditions due to small and large sizes of Cs+ and FA+ ions, respectively. The instability of the black phase of these perovskites hinders their applications in photovoltaic devices as a high-quality light absorber layer. Several approaches have been employed to prevent the formation of the photo-inactive yellow phase or to enhance the stability of the black phase of perovskites, such as dimensional and compositional engineering, the addition of external additives, and dimensional engineering. This perspective summarizes the various methods for stabilizing the black phase of CsPbI3 and FAPbI3 perovskites at room temperature as well as their application in photovoltaic devices.

Supramolecular Recognition within a Nanosized "Buckytrap" That Exhibits Substantial Photoconductivity.

We report here a nanosized "buckytrap", 1, constructed from two bis-zinc(II) expanded-TTF (exTTF) porphyrin subunits. Two forms, 1a and 1b, differing in the axial ligands, H2O vs tetrahydrofuran (THF), were isolated and characterized. Discrete host-guest inclusion complexes are formed upon treatment with fullerenes as inferred from a single-crystal X-ray structural analyses of 1a with C70. The fullerene is found to be encapsulated within the inner pseudohexagonal cavity of 1a. In contrast, the corresponding free-base derivative (2) was found to form infinite ball-and-socket type supramolecular organic frameworks (3D-SOFs) with fullerenes, (2•C60)n or (2•C70)n. This difference is ascribed to the fact that in 1a and 1b the axial positions are blocked by a H2O or THF ligand. Emission spectroscopic studies supported a 1:1 host-guest binding stoichiometry, allowing association constants of (2.0 ± 0.5) × 104 M-1 and (4.3 ± 0.9) × 104 M-1 to be calculated for C60 and C70, respectively. Flash-photolysis time-resolved microwave conductivity (FP-TRMC) studies of solid films of the Zn-complex 1a revealed that the intrinsic charge carrier transport, i.e., pseudo-photoconductivity (ϕ∑µ), increases upon fullerene inclusion (e.g., ϕ∑µ = 1.53 × 10-4 cm2 V-1 s-1 for C60⊂(1a)2 and ϕ∑µ = 1.45 × 10-4 cm2 V-1 s-1 for C70⊂(1a)2 vs ϕ∑µ = 2.49 × 10-5 cm2 V-1 s-1 for 1a) at 298 K. These findings provide support for the notion that controlling the nature of self-assembly supramolecular constructs formed from exTTF-porphyrin dimers through metalation or choice of fullerene can be used to regulate key functional features, including photoconductivity.

Mechanochemically interlocked cubane copper complex interface for WOLED.

In the rapid development of organic light-emitting diodes (OLEDs), phosphorescent transition metal complexes have played a crucial role as the most promising candidates for next generation display and lighting applications. However, most devices are fabricated using iridium and platinum-based complexes which are expensive and available in very limited quantities, whereas using relatively abundant organometallic complexes for fabrication results mostly in inefficient performance results. To overcome these issues, we have synthesized tetra copper iodide with tetra triphenyl cage like structure (denoted as CIPh) as an emerging class of luminescent material by mechanochemical grinding followed by thermal treatment for application in white OLED. The CIPh complex exhibits considerable quantum yield and a millisecond decay lifetime. Phosphorescent OLEDs were fabricated using CIPh complex as emitter shows a remarkable performance with external quantum efficiency and current efficiency of 5.28 % and 22.76 cd/A, with a high brightness of 4200 cd m-2, respectively. White OLEDs were also fabricated with a fluorescent blue and phosphorescent red emitted with (CIPh) as green emitter and achieved an impressive CRI of 82 with an EQE of over 3 %. This is the first ever attempt at fabricating WOLEDs using organocopper complex.

Precursor silanization assisted synthesis and optical tuning of dual-phase perovskite nanocrystals embedded in silica matrix with high environmental stability.

Ligand-assisted re-precipitation (LARP) is one of the most practicing techniques for synthesizing colloidal nanocrystals (NCs). But due to its fast reaction kinetics, it offers limited synthesis control. In the present study, we report a novel, precursor silanization-based room temperature technique unveiling slow crystallization of Cs4PbBr6/CsPbBr3 dual-phase nanocrystals (DPNCs) protected with a dense silica cloud-like matrix. Unlike conventional LARP, we can observe the tuneable optical bandgap of the DPNCs as a function of reaction time because of the slow reaction kinetics. The as-synthesized DPNCs exhibit a high photoluminescence quantum yield (PLQY) of 76% with ultrahigh stability while retaining âˆ¼ 100% of their initial PLQY in an ambient environment with a relative humidity of 55% for more than 1 year. DPNCs demonstrates ambient photostability of 560 h, and water stability of 25 days. This interesting precursor silanization technique developed here can be extended for the synthesis of other nanomaterials.

Oligopyrrolic Cages: From Classic Molecular Constructs to Chemically Responsive Polytopic Receptors.

"Functional molecular systems", discrete and self-assembled constructs where control over molecular recognition, structure, bonding, transport, release, catalytic activity, etc., is readily achieved, are a topic of current interest. Within this broad paradigm, oligopyrrolic cages have garnered attention due to their responsive recognition features. Due to the presence of slightly polar pyrrole subunits which can also behave as hydrogen-bonding donors, these oligopyrrolic cages are potential receptors for various polarized species. In this Account, we summarize recent advances involving the syntheses and study of (1) covalent oligopyrrolic macrobicyclic cages, (2) oligopyrrolic metallacages, and (3) oligopyrrolic noncovalently linked cages. Considered in concert, these molecular constructs have allowed advances in applied supramolecular chemistry; to date, they have been exploited for selective guest encapsulation studies, anion binding and ion-channel formation, and gas absorption, among other applications. While key findings from others will be noted, in this Account will focus on our own contributions to the chemistry of discrete oligopyrrolic macrocycles and their use in supramolecular host-guest chemistry and sensing applications. In terms of specifics, we will detail how oligopyrrole cages with well-defined molecular geometries permit reversible guest binding under ambient conditions and how the incorporation of pyrrole subunits within larger superstructures allows effective control over anion/conjugate acid binding activity under ambient conditions. We will also provide examples that show how derivatization of these rudimentary macrocyclic cores with various sterically congested ß-substituted oligopyrroles can provide entry into more complex supramolecular architectures. In addition, we will detail how hybrid systems that include heterocycles other than pyrrole, such as pyridine and naphthyridine, can be used to create self-assembled materials that show promise as gas-absorbing materials and colorimetric reversible sensors. Studies involving oligopyrrolic polymetallic cages and oligopyrrolic supramolecular cages will also be reviewed. First, we will discuss all-carbon-linked oligopyrrolic bicycles and continue on to present systems linked via amines and imines linkages. Finally, we will summarize recent work on pyrrolic cages created through the use of metal centers or various noncovalent interactions. We hope that this Account will provide researchers with an initial foundation for understanding oligopyrrolic cage chemistry, thereby allowing for further advances in the area. It is expected that the fundamental design and recognition principles made in the area of oligopyrrole cages, as exemplified by our contributions, will be of general use to researchers targeting the design of functional molecular systems. As such, we have structured this Account so as to summarize the past while setting the stage for the future.

Correction: A hybrid blue perovskite@metal-organic gel (MOG) nanocomposite: simultaneous improvement of luminescence and stability.

[This corrects the article DOI: 10.1039/C9SC03829A.].

Modulation of the optical bandgap and photoluminescence quantum yield in pnictogen (Sb3+/Bi3+)-doped organic-inorganic tin(IV) perovskite single crystals and nanocrystals.

Water-stable, lead-free zero-dimensional (0D) organic-inorganic hybrid colloidal tin(IV) perovskite, A2SnX6 (A is a monocationic organic ion and X is a halide) nanocrystals (NCs) with high photoluminescence (PL) quantum yield (QY) have rarely been explored. Herein, we report solution-processed colloidal NCs of blue light-emitting T2SnCl6 and orange light-emitting T2Sn1-xSbxCl6 [T+ = tetramethylammonium cation] from their corresponding single crystals (SCs). These colloidal NCs are well-dispersible in non-polar solvents, thereby maintaining their bright emission. This paves the way for fabricating homogeneous thin films of these NCs. Due to organic cation (T+)-controlled large spin-orbit coupling (SOC), the T2Sn1-xSbxCl6 NCs exhibit bright orange emission with an enhancement in PL QY of 41% compared to their bulk counterpart. Furthermore, we explore T2Sn1-xBixCl6 and T2Sn1-x-yBixSbyCl6 SCs, which show blue and green emission, respectively; the latter is attributed to the newly formed Sb 5p and Sb 5 s orbital-driven band structures confirmed by applying density functional theory (DFT) calculations. The SCs and NCs exhibit excellent stability in water under ambient conditions because of the in-situ generation of a hydrophobic and oxygen-resistant passivating layer of oxychloride in the presence of water. Our findings open a pathway for designing lead-free perovskites materials for thin-film-based optoelectronic devices.

Progress and challenges of graphene and its congeners for biomedical applications.

Nanomaterials by virtue of their small size and enhanced surface area, present unique physicochemical properties that enjoy widespread applications in bioengineering, biomedicine, biotechnology, disease diagnosis, and therapy. In recent years, graphene and its derivatives have attracted a great deal of attention in various applications, including photovoltaics, electronics, energy storage, catalysis, sensing, and biotechnology owing to their exceptional structural, optical, thermal, mechanical, and electrical. Graphene is a two-dimensional sheet of sp2 hybridized carbon atoms of atomic thickness, which are arranged in a honeycomb crystal lattice structure. Graphene derivatives are graphene oxide (GO) and reduced graphene oxide (rGO), which are highly oxidized and less oxidized forms of graphene, respectively. Another form of graphene is graphene quantum dots (GQDs), having a size of less than 20 nm. Contemporary graphene research focuses on using graphene nanomaterials for biomedical purposes as they have a large surface area for loading biomolecules and medicine and offer the potential for the conjugation of fluorescent dyes or quantum dots for bioimaging. The present review begins with the synthesis, purification, structure, and properties of graphene nanomaterials. Then, we focussed on the biomedical application of graphene nanomaterials with special emphasis on drug delivery, bioimaging, biosensing, tissue engineering, gene delivery, and chemotherapy. The implications of graphene nanomaterials on human health and the environment have also been summarized due to their exposure to their biomedical applications. This review is anticipated to offer useful existing understanding and inspire new concepts to advance secure and effective graphene nanomaterials-based biomedical devices.

A bio-compatible pyridine-pyrazole hydrazide based compartmental receptor for Al3+ sensing and its application in cell imaging.

For practical applications, the development of bio-compatible organic molecules as p-block ion chemosensors is critical. Herein, we report the single crystal (SC) of new pyridine-pyrazole derived Al3+ sensor H2PPC [(Z)-N'-(2,3-dihydroxybenzylidene)-5-methyl-1-(pyridin-2-yl)-1H-pyrazole-3-carbohydrazide] as well as its Cu-complex SC. The probe exhibits an "off-on" fluorescence response towards Al3+ ions, and this has been modulated with different solvents. For selective detection of Al3+ ions, a special coordination pocket in the structural backbone is advantageous. The chemosensor exhibits a submicromolar detection level (LOD = 4.78 µM) for Al3+. The density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations of H2PPC and [Al(HPP)2]+ (1) reveal that a change of the structural conformation of probe H2PPC upon complexation causes the pyrazole and pyridine units to create a specific cavity to tether Al3+, and consequently H2PPC proves to be a promising molecule for Al3+ detection. Furthermore, the probe has been successfully used to evaluate Al3+ as a low-cost kit using filter paper strips, and the in situ Al3+ ion imaging in Vero cells as well as A549 cell lines shows the sensor's nuclear envelope penetrability, indicating that it has great potential for biological and environmental applications.

Resonantly Pumped Bright-Triplet Exciton Lasing in Cesium Lead Bromide Perovskites.

The surprising recent observation of highly emissive triplet-states in lead halide perovskites accounts for their orders-of-magnitude brighter optical signals and high quantum efficiencies compared to other semiconductors. This makes them attractive for future optoelectronic applications, especially in bright low-threshold nanolasers. While nonresonantly pumped lasing from all-inorganic lead-halide perovskites is now well-established as an attractive pathway to scalable low-power laser sources for nano-optoelectronics, here we showcase a resonant optical pumping scheme on a fast triplet-state in CsPbBr3 nanocrystals. The scheme allows us to realize a polarized triplet-laser source that dramatically enhances the coherent signal by 1 order of magnitude while suppressing noncoherent contributions. The result is a source with highly attractive technological characteristics, including a bright and polarized signal and a high stimulated-to-spontaneous emission signal contrast that can be filtered to enhance spectral purity. The emission is generated by pumping selectively on a weakly confined excitonic state with a Bohr radius ∼10 nm in the nanocrystals. The exciton fine-structure is revealed by the energy-splitting resulting from confinement in nanocrystals with tetragonal symmetry. We use a linear polarizer to resolve 2-fold nondegenerate sublevels in the triplet exciton and use photoluminescence excitation spectroscopy to determine the energy of the state before pumping it resonantly.

Solvent-Controlled Self-Assembled Oligopyrrolic Receptor.

We report a fully organic pyridine-tetrapyrrolic U-shaped acyclic receptor 10, which prefers a supramolecular pseudo-macrocyclic dimeric structure (10)2 in a less polar, non-coordinating solvent (e.g., CHCl3). Conversely, when it is crystalized from a polar, coordinating solvent (e.g., N,N-dimethylformamide, DMF), it exhibited an infinite supramolecular one-dimensional (1D) "zig-zag" polymeric chain, as inferred from the single-crystal X-ray structures. This supramolecular system acts as a potential receptor for strong acids, e.g., p-toluenesulfonic acid (PTSA), methane sulfonic acid (MSA), H2SO4, HNO3, and HCl, with a prominent colorimetric response from pale yellow to deep red. The receptor can easily be recovered from the organic solution of the host-guest complex by simple aqueous washing. It was observed that relatively stronger acids with pKa < -1.92 in water were able to interact with the receptor, as inferred from 1H NMR titration in tetrahydrofuran-d8 (THF-d8) and ultraviolet-visible (UV-vis) spectroscopic titrations in anhydrous THF at 298 K. Therefore, this new dynamic supramolecular receptor system may have potentiality in materials science research.

Solvent-Regulated Fluorimetric Differentiation of Al3+ and Zn2+ Using an AIE-Active Single Sensor.

The absence of d-orbital electrons or presence of full-filled d-orbital electrons in metal ions is a well-known Achilles' heel problem for the detection of these metal ions by a simple UV-visible study. For this reason, detection of metal ions such as Al3+ with no d-orbital electrons or Zn2+ with filled d-orbital electrons is a challenging task. Herein, we report a 2-naphthol-based fluorescent probe [1-((E)-((E)-(5-bromo-2-hydroxybenzylidene)hydrazono)methyl)naphthalen-2-ol] (H2L) that has been used to sense and discriminate Al3+ and Zn2+ via solvent regulation. The probe exhibits excellent selectivity and swift sensitivity toward Al3+ in MeOH-water (9:1, v/v) and toward Zn2+ in dimethyl sulfoxide (DMSO)-water (9:1, v/v) among various metal ions. The respective detection limit is found to be 9.78 and 3.65 µM. The sensing mechanism is attributed to multiple processes, viz., the inhibition of photo-induced electron transfer (PET) along with the introduction of chelation-enhanced emission (CHEF) and excited-state intramolecular proton transfer (ESIPT) inhibition, which are experimentally well verified by UV-vis absorption spectroscopy, emission spectroscopy, and NMR spectroscopy. The probe shows aggregation-induced emissive (AIE) response in ≥70% aqueous media as well as in the solid state. The experimental results are well corroborated by time-resolved photoluminescence (TRPL) and density functional theory (DFT) calculations. An advanced-level OR-AND-NOT logic gate has been constructed from a different chemical combinational input and emission output. The reversible recognition of both Al3+ in MeOH-water (9:1, v/v) and Zn2+ in DMSO-water (9:1, v/v) is also ascertained in the presence of Na2EDTA, enabling the construction of a molecular memory device. The probe H2L also detects intracellular Al3+/Zn2+ ions in Hela cells. Altogether, our fundamental findings will pave the way for designing and synthesis of unique chemosensors that could be used for cell imaging studies as well as constructing molecular logic gates.

Benzo-Tetrathiafulvalene- (BTTF-) Annulated Expanded Porphyrins: Potential Next-Generation Multielectron Reservoirs.

Two sterically crowded benzo-tetrathiafulvalene (BTTF)-annulated expanded porphyrins (BTTF7-F and BTTF8) are synthesized. Detailed photophysical investigations reveal their intrinsic intramolecular charge transfer (CT) character, originated from partial electron transfer from electron-rich TTF units to the relatively electron-deficient macrocyclic core. This finding stands in contrast to what was observed in the previously reported Figure-of-eight conformer of BTTF-annulated [28]hexaphyrin (BTTF6), in which a typical π-π* electronic transition from HOMO to LUMO was observed. However, core expansion in BTTF7-F and BTTF8 makes the oligopyrrole macrocyclic cores relatively more electron-deficient, facilitating the effective intramolecular CT process. Comparative electrochemical investigations reveal that the current generated at the oxidative region is directly proportional to the number of TTF units attached to the macrocyclic core. This work demonstrates the control of the intramolecular CT process through incremental addition of TTF units to the macrocyclic core. Facile multielectron electrochemical oxidations of these expanded porphyrins suggest that they behave like potential multielectron reservoirs.

Acetate ion augmented fluorescence sensing of Zn2+ by Salen-based probe, AIE character, and application for picric acid detection.

Counter anion-triggered metal ion detection has been rarely reported by fluorimetric method. To address this challenging issue, a fluorescent probe (H2L) has been synthesized from bromo-salicylaldehyde and hydrazine hydrate, and structurally characterized by single crystal X-ray diffraction. The probe shows very weak fluorescence itself. However, its emission intensity increases in the presence of Zn2+ over other metal ions. Surprisingly, the emission profile of this probe in presence of Zn2+ is augmented only when acetate anion (OAc¯) is present as counter anion, that allows for precise quantitative analysis by spectroscopic studies. The compositions and complexation among the probe, Zn2+ ion, and OAc¯ are supported by ESI-MS, 1H-NMR, and Job's plot. Based on these studies, it is confirmed that the binding ratio between probe: metal is 1:2 and the detection limit (LOD) for the Zn2+ is 2.18 µM. The probe is capable of recognizing Zn2+ ion in the wide range of pH∼6.5-9.5, and it could be efficiently recycled by EDTA. Furthermore, the combinatorial molecular logic gate and memory device have been constructed from the fluorescent behavior of H2L with Zn2+, OAc¯, and EDTA input as based on NOT and AND gates. Interestingly, the aggregation-induced emission (AIEE) phenomenon is also perceived with greater than 50% water content in organic water mixtures, which are then useful for the detection of picric acid often used as explosive.