A bidentate borane as colorimetric fluoride ion sensor

π-Extended 9b-Boraphenalenes: Synthesis, Structure, and Physical Properties

Boraphenalenes, compounds in which one carbon atom in the phenalenyl skeleton is replaced with a boron atom, have attracted attention for their solid-state and electronic structures; however, the construction of boraphenalene skeletons remains challenging because of the lack of suitable methods. Through this study, we showed that the tandem borylative cyclization of C3-symmetric dehydrobenzo[12]annulenes produces a new class of fully fused boron-atom-embedded polycyclic hydrocarbons possessing a 9b-boraphenalene skeleton. The obtained compounds exhibited high electron-accepting characteristics, and their two-step redox process was reversible in the reductive region, involving interconversion of 9b-boraphenalene between Hückel aromaticity and antiaromaticity. Notably, the benzo[b]fluorene-fused derivative exhibited a stepwise single-crystal-to-single-crystal (SCSC) phase transition triggered by thermal annealing. Intermolecular electron coupling calculation of the crystal structures suggested a significant improvement of charge transporting ability associated with the SCSC phase transition. Moreover, adequate photoconductivity was observed for the single crystals before and after the SCSC phase transition through flash photolysis-time-resolved microwave conductivity.

Anion-Responsive Colorimetric and Fluorometric Red-Shift in Triarylborane Derivatives: Dual Role of Phenazaborine as Lewis Acid and Electron Donor

Photophysical modulation of triarylboranes (TABs) through Lewis acid-base interactions is a fundamental approach for sensing anions. Yet, design principles for anion-responsive TABs displaying significant red-shift in absorption and photoluminescence (PL) have remained elusive. Herein, a new strategy for modulating the photophysical properties of TABs in a red-shift mode has been presented, by using a nitrogen-bridged triarylborane (1,4-phenazaborine: PAzB) with a contradictory dual role as a Lewis acid and an electron donor. Following the strategy, PAzB derivatives connected with an electron-deficient azaaromatic have been developed, and these compounds display a distinct red-shift in their absorption and PL in response to an anion. Spectroscopic analyses and quantum chemical calculations have revealed the formation of a tetracoordinate borate upon the addition of fluoride, narrowing the HOMO-LUMO gap and enhancing the charge-transfer character in the excited state. This approach has also been demonstrated in modulating the photophysical properties of solid-state films.

Heteroatom-Promoted Polyhexagonal Saddle-Shaped Molecular Structures and their Supramolecular Coassembly with C60

Molecules with curved architecture can exhibit unique optoelectronic properties due to the concave-convex π-surface. However, synthesizing negatively curved saddle-shaped aromatic systems has been challenging due to the internal structural strain. Herein, we report the facile synthesis of two polyhexagonal molecular systems, 1 and 2, with saddle shape geometry by judiciously varying the aromatic moiety, avoiding the harsh synthetic methods as that of heptagonal aromatic saddle systems. The unique geometry preferences of B, N, and S furnish suitable curvature to the molecules, featuring saddle shape. The saddle geometry also enables them to interact with fullerene C60 , and the supramolecular interactions of fullerene C60 with 1 and 2 modify their optoelectronic properties. Crystal structure analysis reveals that 1, with a small π-surface, forms a double columnar array of fullerenes in the solid state. In contrast, 2 with a large π-surface produces a supramolecular capsule entrapping two discrete fullerenes. The intermolecular interactions between B, N, S, and the aryl-π surface of the host and C60 guest are the stabilizing factors for creating these supramolecular structures. Comprehensive computational, optical, and Raman spectroscopic studies establish the charge transfer interactions between B-N doped heterocycle host and fullerene C60 guest.

Bidentate boron Lewis acids: synthesis by tin boron exchange reaction and host-guest complex formation

Four bidentate boron Lewis acids based on the 1,8-diethynylanthracene backbone have been synthesized by a tin-boron exchange reaction with various chloroboranes, yielding the products in good to excellent yields. Complexation experiments of the host compounds with pyridine, pyrimidine and TMEDA demonstrated striking differences in terms of formation and solubility of the supramolecular adducts. The host-guest complexes were investigated by multinuclear NMR spectroscopy and structurally characterized by X-ray diffraction experiments, illustrating the adaptation of the host system upon adduct formation with different neutral guest molecules.

A Bidentate Ligand Featuring Ditopic Lewis Acids in the Second Sphere for Selective Substrate Capture and Activation

We present a ligand platform featuring appended ditopic Lewis acids to facilitate capture/activation of diatomic substrates. We show that incorporation of two 9-borabicyclo[3.3.1]nonane (9-BBN) units on a single carbon tethered to a pyridine pyrazole scaffold maintains a set of unquenched nitrogen donors available to coordinate FeII , ZnII , and NiII . Using hydride ion affinity and competition experiments, we establish an additive effect for ditopic secondary sphere boranes, compared to the monotopic analogue. These effects are exploited to achieve high selectivity for binding NO2 - in the presence of competitive anions such as F- and NO3 - . Finally, we demonstrate hydrazine capture within the second-sphere of metal complexes, followed by unique activation pathways to generate hydrazido and diazene ligands on Zn and Fe, respectively.

Recent Advances in the Synthesis of Borinic Acid Derivatives

Borinic acids [R2B(OH)] and their chelate derivatives are a subclass of organoborane compounds used in cross-coupling reactions, catalysis, medicinal chemistry, polymer or optoelectronics materials. In this paper, we review the recent advances in the synthesis of diarylborinic acids and their four-coordinated analogs. The main strategies to build up borinic acids rely either on the addition of organometallic reagents to boranes (B(OR)3, BX3, aminoborane, arylboronic esters) or the reaction of triarylboranes with a ligand (diol, amino alcohol, etc.). After general practical considerations of borinic acids, an overview of the main synthetic methods, their scope and limitations is provided. We also discuss some mechanistic aspects.

Boronic ester functionalised 1,8-diboryl-naphthalene scaffolds: fluoride versus oxide chelation

1,8-Bis(boronic ester) derivatives of naphthalene, 1,8-C10H6{B(OR)2}2, present an attractive target as receptors for the fluoride ion via B-F-B chelation, but are synthetically challenging to access due to the competing formation of a very stable anhydride containing a B-O-B motif. By contrast, unsymmetrical systems of the type 1,8-C10H6{B(OR)2}(BR'2) can be synthesized for (OR)2 = 1,2-O2C6H4 (i.e. Cat) and R' = Mes. This system is shown to be competent for the uptake of F-, making use of a chelating mode of action and the formation of a bridging B-F-B motif between the two boron centres. However, both experimental and quantum chemical studies indicate that the μ2-F adduct is the kinetic product of fluoride uptake, with an alternative structural motif featuring a terminal B-F bond and a B-O-B bridge using one of the catechol oxygens being (marginally) more favourable thermodynamically.

Synthesis of B/Si Bidentate Lewis Acids, o-(Fluorosilyl)borylbenzenes and o-(Difluorosilyl)borylbenzenes, and Their Fluoride Ion Affinities

Herein, we report detailed studies on a series of o-(silyl)(boryl)benzenes (1-4), in which the two Lewis acid centers consisting of silicon and boron atoms are linked via an o-phenylene skeleton. o-(Fluorosilyl)(dimesitylboryl)benzenes 1 and 2 were prepared by the reaction of fluorodimesitylborane with [o-(fluorodimethylsilyl)phenyl]lithium (7) and [o-(fluorodiphenylsilyl)phenyl]lithium (8), respectively. o-(Difluorosilyl)(dimesitylboryl)benzenes 3 and 4 were also prepared by the reaction of fluorodimesitylborane with o-{[di(methoxy)methylsilyl]phenyl}lithium (11) and o-{[di(methoxy)phenylsilyl]phenyl}lithium (12), respectively, and their subsequent treatment with HF·pyridine. Compounds 1-4 readily capture a fluoride ion in the presence of 18-crown-6 or [2.2.2]cryptand to afford their corresponding μ-fluoro-bridged ate complexes (15-18). The structures of 15-18 were revealed by NMR spectroscopy and X-ray crystallography. DFT studies and natural bond orbital analysis of 15-18 were conducted to elucidate the nature of the Si-F and B-F bonding interactions in the μ-fluoro-bridges. The fluoride ion affinities of 1-4 were investigated by ¹H NMR spectroscopy to monitor their competitive reactions. The dynamic behaviors of 15-18 at variable temperatures were monitored using ¹⁹F NMR spectroscopy.

Fluoride ion sensing with an acridinium borane

With our continuing interest in the chemistry of cationic boranes, we have synthesizedthe tetrafluoroborate salt of 1-dimesitylboron-4-(N-methyl-9-acridinium)-phenylene which acts as a turn-on fluoride anion sensor, visibly changing from yellow to orange upon binding fluoride. To understand this reactivity, we spectroscopically and computationally analyzed the cation and triarylfluoroborate adduct. UV-vis spectroscopy and TD-DFT revealed the basis of the color change to be a red shift in a low-energy absorption band resulting from intramolecular charge-transfer. Electrochemical studies were undertaken to further probe this system. Cyclic voltammetry indicated a reversible one-electron reduction for the cation and a cathodic shift of -0.12 V in the first reduction wave upon fluoride binding. Chemical reduction of the cation yielded the acridine borane radical which was verified by EPR spectroscopy.

Tuning Diradical Properties of Boron-Containing π-Systems by Structural Isomerism

Tuning diradical character is an important topic for organic diradicaloids. Herein, we report the precise borylation enabling structural isomerism as an effective strategy to modulate diradical character and thereby properties of organic diradicaloids. We synthesized a new B-containing polycyclic hydrocarbon that has the indeno[1,2-b]fluorene π-skeleton with the β-carbons bonding to two boron atoms. Detailed theoretical and experimental results show that this bonding pattern leads to its distinctive electronic structures and properties in comparison to that of its isomeric molecule. This molecule has the efficient conjugation between boron atoms and π-skeleton, resulting in downshifted LUMO and HOMO levels. Moreover, it exhibits smaller diradical character and thereby inhibited diradical properties, such as significantly blue-shifted light absorption, larger energy bandgap and weak para-magnetic resonance. Notably, this B-containing polycyclic hydrocarbon possesses much stronger Lewis acidity and its Lewis acid-base adducts display enhanced diradical character, demonstrating the positive effects of Lewis coordination on modulating diradical performance.

Fluorescent small molecules with alternating triarylamine-substituted selenophenothiophene and triarylborane: synthesis, photophysical properties and anion sensing studies

Two novel D-π-A fluorophores based on selenopheno[3,2-b]thiophene, possessing triphenylamine and 4,4'-dimethoxytriphenylamine units as donors and dimesitylborane as an acceptor, linked through a π-conjugated thiophene spacer (BTPAST and BOMeTPAST, respectively) were synthesized. Their photophysical properties were investigated in both solution and the state of aggregation and compared to those of their corresponding donor parts, having no dimesitylborane units (TPAST and OMeTPAST). All the compounds displayed large Stokes shifts between 100 and 140 nm with positive solvatochromism in solvents having different polarities. While BTPAST displayed both aggregation induced emission (AIE) and twisted intramolecular charge transfer (TICT) characteristics, the others preponderated with TICT effects. The sensing abilities of BTPAST and BOMeTPAST towards different anions were studied. Both exhibited chromogenic and fluorogenic responses to small anions such as fluoride and cyanide, for which the detection limits were found to be 0.12 and 2.43 ppm with BTPAST and 0.59 and 0.92 ppm with BOMeTPAST, respectively. These results provide guidance for the development of novel fused selenophenothiophene sensors in the field of anion sensing.

Boron-Containing Organic Diradicaloids: Dynamically Modulating Singlet Diradical Character by Lewis Acid-Base Coordination

Organic diradicaloids have unique open-shell structures and properties and promising applications in organic electronics and spintronics. Incorporation of heteroatoms is an effective strategy to alter the electronic structures of organic diradicaloids. However, B-containing organic diradicaloids are very challenging due to their high reactivities, which are caused by not only diradical nature but also the B atom. In this article, we report a new kind of organic diradicaloids containing boron atoms. Our strategy is to incorporate planarized triarylboranes to antiaromatic polycyclic hydrocarbons (PHs). We synthesized two isomeric B-containing PHs composed of indenofluorene π-skeletons and two dioxa-bridged triphenylborane moieties. As proved by theoretical and experimental results, both of them have excellent ambient stability and open-shell singlet diradical structures, as well as intriguing magnetic and optoelectronic properties, such as thermally accessible triplet species, reversible multiredox ability, and narrow energy gaps. Notably, they possess sufficient Lewis acidity, which has never been observed for organic diradicaloids. In addition, they can coordinate with Lewis bases to form Lewis adducts, achieving unprecedented dynamic modulations of (anti)aromaticity and thus diradical character of organic diradicaloids.

Highly Electron-Deficient Dicyanomethylene-Functionalized Triarylboranes with Low-Lying LUMO and Strong Lewis Acidity

A series of dicyanomethylene-functionalized triarylboranes is reported in this work, with low-lying LUMO energy levels at ca. -3.66 eV for ^FMesB-ACN. The single-crystal structures of the mono- and dianion of Mes*B-ACN were obtained via chemical reduction, which revealed a conversion from a quinoidal to an aromatic structure. The strong Lewis acidity of these compounds is reflected in a fluoride-anion binding experiment. This work introduces a facile strategy for modulating the electron deficiency of boron-containing compounds.

Distiboranes based on ortho-phenylene backbones as bidentate Lewis acids for fluoride anion chelation

As part of our efforts in the chemistry of main group platforms that support anion sensing and transport, we are now reporting the synthesis of anitmony-based bidentate Lewis acids featuring the o-C6F4 backbone. These compounds can be easily accessed by reaction of the newly synthesized o-C6F4(SbPh2)2 (5) with o-chloranil or octafluorophenanthra-9,10-quinone, affording the corresponding distiboranes 6 and 7 of general formula o-C6F4(SbPh2(diolate))2 with diolate = tetrachlorocatecholate for 6 and octafluorophenanthrene-9,10-diolate for 7, respectively. While 6 is very poorly soluble, its octafluorophenanthrene-9,10-diolate analog 7 readily dissolves in CH2Cl2 and undergoes swift conversion into the corresponding fluoride chelate complex [7-μ2-F]- which has been isolated as a [nBu4N]+ salt. The o-C6H4 analog of 7, referred to as 8, has also been prepared. Although less Lewis acidic than 7, 8 also forms a very stable fluoride chelate complex ([8-μ2-F]-). Altogether, our experiental results, coupled with computational analyses and fluoride anion affinity calculations, show that 7 and 8 are some of the strongest antimony-based fluoride anion chelators prepared to date. Another notable aspect of this work concerns the use of the octafluorophenanthrene-9,10-diolate ligand and its ablity to impart advantageous solubility and Lewis acidity properties.

Hydrogen-bond-induced selectivity of a head-to-head photo-dimerisation of dialkynylanthracene - access to tetradentate Lewis acids

Using 2-hydroxypropyl-protecting groups, 1,8-dialkynylanthracene photo-dimers were prepared in head-to-head-configuration by UV irradiation on a multi-gram scale. In non-polar solvents, the combination of non-covalent hydrogen bonds and π-π-interactions induces the formation of the syn-isomer in up to 85% yield. Instead, more polar solvents or irradiation of unprotected 1,8-diethynylanthracene led to formation of the corresponding anti-isomer in large excess. Cleavage of the protecting groups under basic conditions affords a rigid hydrocarbon skeleton with four directional functions. This was used as a building block for a tetradentate boron Lewis acid. Its applicability as a host for Lewis-base substrates was demonstrated by the formation of adducts with various nitrogen bases. Adduct formation with hydrazine leads to impressive networks between the tetraboron host and the substrate molecules.

Molecular Conformational Effect on Optical Properties and Fluoride Induced Color Changes in Triarylborane-Vinylbithiophene-BODIPY Conjugates

Three new triads [bis(mesityl)boryl (Mes₂B)-vinylbithiophene-BODIPY] bearing zero (1), two (2), and four (3) methyl groups on the BODIPY core are synthesized, and their optical properties are reported. The vinyl linker between the thiophene rings in the spacer moiety improved the electronic communication between the boryl and BODIPY units. It displayed a bathochromic shift in the absorption and emission spectra compared to the Mes₂B-bithiophene-BODIPY triad reported elsewhere. These compounds exhibit intriguing multiple-emission features due to an incomplete energy transfer from donor borane to the acceptor BODIPY unit. These compounds' photoluminescence color can be conveniently fine-tuned by fluoride binding at the coordinatively unsaturated tricoordinate boron center. Triad 3, with a rigid molecular structure, showed a sharp emission band, whereas triads 1 and 2, with flexible molecular structures, displayed broad emission bands with a robust bathochromic shift, ascribed to their excited state structural reorganizations. These triads selectively bind fluoride ions and show colorimetric responses, which can be seen with an unaided eye. DFT computational studies were performed to rationalize the optical signatures of these compounds.

Temperature-sensitive triarylboron compounds based on naphthalene substituents

Since temperature is one of the most important physical parameters, it is of great significance to measure temperature with high space resolution and accuracy. Herein, a series of π-conjugated triarylboron compounds with temperature sensitivity based on naphthalene aromatic groups were designed and synthesized. Their photophysical properties were studied in detail by steady state absorption, emission spectroscopy and time-dependent density functional theory calculation. As the temperature increased, their emission spectra exhibited obvious blue shifts in liquid organic solvent, making ratiometric fluorescence sensing of temperature achievable.

A Colorimetric Chemosensor Based on a Nozoe Azulene That Detects Fluoride in Aqueous/Alcoholic Media

Colorimetry is an advantageous method for detecting fluoride in drinking water in a resource-limited context, e. g., in parts of the developing world where excess fluoride intake leads to harmful health effects. Here we report a selective colorimetric chemosensor for fluoride that employs an azulene as the reporter motif and a pinacolborane as the receptor motif. The chemosensor, NAz-6-Bpin, is prepared using the Nozoe azulene synthesis, which allows for its rapid and low-cost synthesis. The chemosensor gives a visually observable response to fluoride both in pure organic solvent and also in water/alcohol binary solvent mixtures.

Synthesis, structure and anion binding properties of 1,8-bis(dimesitylboryl)anthracene and its monoborylated analog

Two boranes, 1-(dimesitylboryl)anthracene (1) and 1,8-bis(dimesitylboryl)anthracene (2), have been synthesized with the spectrophysical properties showing how the inclusion of one or two boron atoms progressively perturbs the π-system of the anthracene backbone. This perturbation is caused by conjugation of the anthracene-π* orbital with the vacant p-orbital on boron. Additionally, both 1 and 2 have a high affinity for fluoride and cyanide anions which are complexed in a 1 : 1 guest-host ratio. The mono-borane 1 is particularly well-suited for cyanide binding, displaying a binding constant of 3 × 107 in THF. Furthermore, as a result of their unique electronic structures, these boranes display a fluorescence response to fluoride anion characterized by a blue shift in the case of 1 and a red shift in the case of 2.

Polymorphism and pseudosymmetry of 10,10'-oxybis(9-thia-10-hydro-10-boraanthracene)

We have encountered two polymorphs of the title compound, C24H16B2OS2, both of which display almost the same unit-cell parameters. Compound (I) crystallizes in the non-centrosymmetric space group P21 with four mol-ecules in the asymmetric unit. These mol-ecules are related by pseudosymmetry. As a result, the space group looks like P21/c, but the structure cannot be refined successfully in that space group. Compound (II) on the other hand crystallizes in the centrosymmetric space group P21/c with only two mol-ecules in the asymmetric unit. The crystals studied for (I) and (II) were both non-merohedral twins.

Pyrazinoindole-Based Lewis-Acid/Base Assembly: Intriguing Intramolecular Charge-Transfer Switching through the Dual-Sensing of Fluoride and Acid

Pyrazinoindole-based Lewis-acid/base assemblies are prepared through the use of regioselective formal [3 + 3] cycloaddition reactions, and their intriguing photophysical properties are described. The assemblies exhibit strong emissions in THF solution, which are attributed to through-space intramolecular charge-transfer (ICT) transitions between the branched Lewis-acid/base moieties. Furthermore, these show ratiometric color-change responses in PL titration experiments, which give rise to new colors through turn-on emissions ascribable to ICT transitions that alternate between the pyrazinoindole units and each triarylboryl or amino moiety, a consequence of the binding of the fluoride or acid. Pieces of filter paper covered by these assemblies exhibited blue-shifted color changes when immersed in aqueous acidic solutions, suggesting that these are promising candidate indicators that detect acid through emissive color. Computational data for these assemblies and their corresponding adducts verify the existence of ICT transitions that alternate through fluoride or acid binding.

Bidentate Boron Lewis Acids: Selectivity in Host-Guest Complex Formation

Bidentate boron Lewis acids based on 1,8-diethynylanthracene were synthesised in two steps by initial stannylation of the terminal alkynes and subsequent tin-boron exchange with different chloroboranes. The reactions were very selective, and the target compounds were obtained in high purity and good to excellent yields. Complexation experiments of 1,8-bis[(diphenylboranyl)ethynyl]anthracene with nitrogen bases (pyridine, pyrimidine, TMEDA) afforded three stable adducts, which were structurally characterised by X-ray diffraction. Competition experiments demonstrated the selective exchange of guests, and quantum-chemical calculations provided information on their energetics. NMR experiments at low temperature gave insight into the dynamic behaviour of the TMEDA adduct.

Supramolecular Pt(II) and Ru(II) Trigonal Prismatic Cages Constructed with a Tris(pyridyl)borane Donor

We report a novel example of supramolecular cages containing a Lewis acidic trigonal boron center. Self-assembly of the tris(pyridyl)borane donor 1 with diruthenium (2) or platinum (3), as an electron acceptor, furnished boron-containing trigonal prismatic supramolecular cages 5 and 6, which were characterized by 1H NMR and electrospray ionization time-of-flight mass spectroscopy and X-ray crystallography. The molecular structure of cage 5 was confirmed as a trigonal prismatic cage with an inner dimension of about 400 Å3. The fluoride binding properties of borane ligand 1 and Pt cage 6 were studied. UV/vis absorption titration studies demonstrated that the boron center of cage 6 undergoes strong binding interaction with the fluoride ion, with an estimated binding constant of 1.3 × 1010 M-2 in acetone based on the 1:2 binding isotherm. The binding was also confirmed by 1H NMR titration. Photoluminescence titration studies showed that cage 6 emitted borane-centered fluorescence (τ = 2.21 ns), which was gradually quenched upon addition of fluoride. When excess fluoride was added to a solution of 6, however, dissociation of the pyridyl ligand from the Pt(II) center was observed.

A planarized B-phenyldibenzoborepin: impact of structural constraint on its electronic properties and Lewis acidity

Planarization of B-phenyldibenzo[b,f]borepin allows π-expansion across the B-phenyl group and makes this scaffold a useful electron-accepting unit for donor-π-acceptor type fluorophores.

Non-Planar [n]Cyclo-1,8-carbazolylenes (n=3,4,6) and [3]Cyclo-1,8-carbazolylenyl B, P, PO, SiPh Complexes

A new family of non-planar heterocyclic molecules consisting of carbazoles was created. A bowl-shaped cyclodimer, a flake-shaped cyclotrimer, a double-decker-ring-shaped cyclotetramer and a cyclohexamer were synthesized by Ni⁰ -mediated one-shot cyclo-oligomerization of 1,8-dibromocarbazole, and were named [n]cyclo-1,8-carbazolylenes (n=3,4,6). [3]Cyclo-1,8-carbazolylene was found to act as a trivalent tridentate ligand for heteroatoms (B, P, Si), giving flake-shaped complexes. The boron derivative acted as a Lewis acid, and the tetra-coordinated complexes showed an unprecedented red-shift of absorption and emission spectra by the coordination. The synthetic method, the distorted C₂ or C₁ symmetric shape, the trivalent tridentate coordination ability and the kinds of introduced heteroatoms of [3]cyclo-1,8-carbazolylenes, the electronic structure, the photophysical property, and the Lewis acidity were distinct from those of related subporphyrins/subphthalocyanines.

Crystal structure of bis(2-(2′-hydroxy-5′-methoxyphenyl)-1H-benzimidazole)boron – tetrahydrofuran (1/1), C36H37N4O6B

C36H37N4O6B, monoclinic, C2/c, a = 9.3404(4) Å, b = 19.8395(10) Å, c = 17.8985(9) Å, β = 103.301(5)°, V = 3226.0(3) Å3, Z = 4, R gt(F) = 0.0626, wR ref(F 2) = 0.2086, T = 293 K.

Recent developments in and perspectives on three-coordinate boron materials: a bright future

The empty p z -orbital of a three-coordinate organoboron compound leads to its electron-deficient properties, which make it an excellent π-acceptor in conjugated organic chromophores. The empty p-orbital in such Lewis acids can be attacked by nucleophiles, so bulky groups are often employed to provide air-stable materials. However, many of these can still bind fluoride and cyanide anions leading to applications as anion-selective sensors. One electron reduction generates radical anions. The π-acceptor strength can be easily tuned by varying the organic substituents. Many of these compounds show strong two-photon absorption (TPA) and two-photon excited fluorescence (TPEF) behaviour, which can be applied for e.g. biological imaging. Furthermore, these chromophores can be used as emitters and electron transporters in OLEDs, and examples have recently been found to exhibit efficient thermally activated delayed fluorescence (TADF). The three-coordinate organoboron unit can also be incorporated into polycyclic aromatic hydrocarbons. Such boron-doped compounds exhibit very interesting properties, distinct from their all-carbon analogues. Significant developments have been made in all of these areas in recent years and new applications are rapidly emerging for this class of boron compounds.

Structurally simple azo based chromogenic R1 for the selective sensing of cyanide ion in aqueous medium

Structurally simple azo linked Schiff base R1 was synthesized and characterized using IR, ¹H NMR and mass spectroscopic techniques. The selective sensing of cyanide anion over other anions such as fluoride, chloride, bromine, iodide, acetate, nitrate, hydrogen sulphate and dihydrogenphosphate was revealed by naked-eye color change and UV-vis spectra. Addition of CN^- ions to the R1 showed a dramatic change in color from pale yellow to intense yellow along with the formation of a new band at 415nm in the absorption spectrum even in 100% aqueous medium. The interaction between R1 and cyanide was also investigated using ¹H NMR titration study. The R1 showed limit of detection (LOD) up to micromolar level at 2.72×10^-6M. Job's plot reveals the existing binding mode of R1 and CN^- ion in molar ratio of 1:1 (R1:CN^-).

Synthesis and photophysical properties of phenanthroimidazole–triarylborane dyads: intriguing ‘turn-on’ sensing mediated by fluoride anions

Phenanthroimidazole-based triarylborane compounds with an N-phenyl or N-biphenyl bridge were prepared and these compounds show ratiometrical ‘turn-on’ response in PL spectra upon fluoride binding to the borane moiety.

Microaxicave colour analysis system for fluoride concentration using a smartphone

Layout of our fluoride measurement system and the correlation between the concentration of fluoride and the peak of value–hue curves.