A bidentate borane as colorimetric fluoride ion sensor

Luminescence properties of C-diazaborolyl-ortho-carboranes as donor-acceptor systems

Seven derivatives of 1,2-dicarbadodecaborane (ortho-carborane, 1,2-C(2)B(10)H(12)) with a 1,3-diethyl- or 1,3-diphenyl-1,3,2-benzodiazaborolyl group on one cage carbon atom were synthesized and structurally characterized. Six of these compounds showed remarkable low-energy fluorescence emissions with large Stokes shifts of 15100-20260 cm(-1) and quantum yields (Φ(F)) of up to 65% in the solid state. The low-energy fluorescence emission, which was assigned to a charge-transfer (CT) transition between the cage and the heterocyclic unit, depended on the orientation (torsion angle, ψ) of the diazaborolyl group with respect to the cage C-C bond. In cyclohexane, two compounds exhibited very weak dual fluorescence emissions with Stokes shifts of 15660-18090 cm(-1) for the CT bands and 1960-5540 cm(-1) for the high-energy bands, which were assigned to local transitions within the benzodiazaborole units (local excitation, LE), whereas four compounds showed only CT bands with Φ(F) values between 8-32%. Two distinct excited singlet-state (S(1)) geometries, denoted S(1)(LE) and S(1)(CT), were observed computationally for the benzodiazaborolyl-ortho-carboranes, the population of which depended on their orientation (ψ). TD-DFT calculations on these excited state geometries were in accord with their CT and LE emissions. These C-diazaborolyl-ortho-carboranes were viewed as donor-acceptor systems with the diazaborolyl group as the donor and the ortho-carboranyl group as the acceptor.

Multistage complexation of fluoride ions by a fluorescent triphenylamine bearing three dimesitylboryl groups: controlling intramolecular charge transfer

A propeller-shaped boron-nitrogen compound (NB(3)) with three binding sites for fluoride anions was synthesized and investigated by optical absorption, luminescence, and ((1)H, (11)B, (13)C, (19)F) NMR spectroscopy. Binding of fluoride in dichloromethane solution occurs in three clearly identifiable steps and leads to stepwise blocking of the three initially present nitrogen-to-boron charge transfer pathways. As a consequence, the initially bright blue charge transfer emission is red-shifted and decreases in intensity, until it is quenched completely in presence of large fluoride excess. Fluoride binding constants were determined from global fits to optical absorption and luminescence titration data and were found to be K(a1) = 4 × 10(7) M(-1), K(a2) = 2.5 × 10(6) M(-1), and K(a3) = 3.2 × 10(4) M(-1) in room temperature dichloromethane solution. Complexation of fluoride to a given dimesitylboryl site increases the electron density at the central nitrogen atom of NB(3), and this leads to red shifts of the remaining nitrogen-to-boron charge transfer transitions involving yet unfluorinated dimesitylboryl groups.

A highly Lewis acidic triarylborane bearing peripheral o-carborane cages

A triarylborane (2) bearing three o-carborane cages at peripheral positions on the aryl groups was prepared and its crystal structure was determined from X-ray diffraction study. Treatment of 2 with KF in the presence of 18-crown-6 led to the potassium salt, [2F](-). A UV-vis titration experiment carried out in THF/H(2)O (9/1 v/v) showed that 2 binds fluoride ions with a binding constant (K) of 4.8 × 10(4) M(-1), which is an order-of-magnitude greater than K for the mono-carborane substituted triarylborane. The enhanced fluoride ion affinity of 2 indicates an apparent additive effect of multiple carborane substitutions on the Lewis acidity enhancement of the triarylborane. The highly Lewis acidic nature of 2 was further utilized in evaluating the fluoride ion affinity of tris(pentafluorophenyl)borane (B(C(6)F(5))(3)). A fluoride exchange reaction between [2F](-) and B(C(6)F(5))(3) resulted in 15 times higher fluorophilicity for B(C(6)F(5))(3) than for 2. The lower Lewis acidity of 2 compared with B(C(6)F(5))(3) was confirmed from its greater cathodic reduction potential.

Chromogenic and fluorogenic chemosensors and reagents for anions. A comprehensive review of the year 2009

This critical review is focused on examples reported in the year 2009 dealing with the design of chromogenic and fluorogenic chemosensors or reagents for anions (264 references).

A reaction-based chromogenic and fluorescent chemodosimeter for fluoride anions

An innovative trihexylsilylacetylene-containing BODIPY dye was designed and proved to be a highly selective, sensitive, and fast chromogenic and fluorescent chemodosimeter for fluorides.

DFT/TDDFT investigation of the modulation of photochromic properties in an organoboron-based diarylethene by fluoride ions

The diarylethene derivative 1,2-bis-(5'-dimesitylboryl-2'-methylthieny-3'-yl)-cyclopentene (1) containing dimesitylboryl groups is an interesting photochromic material. The dimesitylboryl groups can bind to F(-), which tunes the optical and electronic properties of the diarylethene compound. Hence, the diarylethene derivative 1 containing dimesitylboryl groups is sensitive to both light and F(-), and its photochromic properties can be tuned by a fluoride ion. Herein, we studied the substituent effect of dimesitylboron groups on the optical properties of both the closed-ring and open-ring isomers of the diarylethene molecule by DFT/TDDFT calculations and found that these methods are reliable for the determination of the lowest singlet excitation energies of diarylethene compounds. The introduction of dimesitylboron groups to the diarylethene compound can elongate its conjugation length and change the excited-state properties from π→π* transition to a charge-transfer state. This explains the modulation of photochromic properties through the introduction of dimesitylboron groups. Furthermore, the photochromic properties can be tuned through the binding of F(-) to a boron center and the excited state of the diarylethene compound is changed from a charge-transfer state to a π→π* transition. Hence, a subtle control of the photochromic spectroscopic properties was realized. In addition, the changes of electronic characteristics by the isomerization reaction of diarylethene compounds were also investigated with theoretical calculations. For the model compound 2 without dimesitylboryl groups, the closed-ring isomer has better hole- and electron-injection abilities, as well as higher charge-transport rates, than the open-ring isomer. The introduction of dimesitylboron groups to diarylethene can dramatically improve the charge-injection and -transport abilities. The closed isomer of compound 1 (1 C) has the best hole- and electron-injection abilities, whereas the charge-transport rates of the open isomer of compound 1 (1 O) are higher than those of 1 C. Importantly, 1 O is an electron-accepting and -transport material. These results show that the diarylethene compound containing dimesitylboryl groups has promising potential to be applied in optoelectronic devices and thus is worth to be further investigated.

Extending pi-conjugation of triarylborons with a 2,2-bpy core: impact of donor-acceptor geometry on luminescence, anion sensing, and metal ion binding

Four new 2,2'-bipyridine-based molecules functionalized by either BMes(2)-phenyl (Mes = mesityl) or NPh(2)-phenyl--5,5'-(p-BMes(2)-phenyl)(2)-2,2'-bpy (5,5'-BP2bpy, 1), 4,4'-(p-BMes(2)-phenyl)(2)-2,2'-bpy (4,4'-BP2bpy, 2), 4-(p-BMes(2)-phenyl)-4'-(p-NPh(2)-phenyl)-2,2'-bipy (4,4'-BPNPbpy, 4), and 4,4'-(p-NPh(2)-phenyl)(2)-2,2'-bpy (4,4'-NP2bpy, 5)--have been synthesized. Their complexes with PtPh(2) have been synthesized and fully characterized. The electronic and photophysical properties of the new molecules have been examined by electrochemical, absorption, and luminescence spectroscopic analysis and DFT calculations, which show significant differences from those of the related but smaller 2,2'-bpy derivatives functionalized directly by either BMes(2) or NPh(2) groups that we reported previously. Molecules 1, 2, and 4 and their Pt(II) complexes respond to fluoride ions in both absorption and emission modes. The donor-acceptor molecule 4 and its Pt(II) complex have a distinct fluorescence/phosphorescence turn-on response toward fluoride or cyanide ions. Molecules 1, 2, 4, and 5 also respond to Zn(II) ions in both absorption and emission modes. The diboryl molecules 1 and 2 have a distinct and contrasting fluorescence response toward Zn(II) ion--turn-off for 1 and turn-on for 2--demonstrating the significant impact of molecular geometry on metal ion binding and fluorescence.