Sheri Madhu

Boron-dipyrromethene based reversible and reusable selective chemosensor for fluoride detection.

We synthesized benzimidazole substituted boron-dipyrromethene 1 (BODIPY 1) by treating 3,5-diformyl BODIPY 2 with o-phenylenediamine under mild acid catalyzed conditions and characterized by using various spectroscopic techniques. The X-ray structure analysis revealed that the benzimidazole NH group is involved in intramolecular hydrogen bonding with fluoride atoms which resulted in a coplanar geometry between BODIPY and benzimidazole moiety. The presence of benzimidazole moiety at 3-position of BODIPY siginificantly altered the electronic properties, which is clearly evident in bathochromic shifts of absorption and fluorescence bands, improved quantum yields, increased lifetimes compared to BODIPY 2. The anion binding studies indicated that BODIPY 1 showed remarkable selectivity and specificity toward F(-) ion over other anions. Addition of F(-) ion to BODIPY 1 resulted in quenching of fluorescence accompanied by a visual detectable color change from fluorescent pink to nonfluorescent blue. The recognition mechanism is attributed to a fluoride-triggered disruption of the hydrogen bonding between BODIPY and benzimidazole moieties leading to (i) noncoplanar geometry between BODIPY and benzimidazole units and (ii) operation of photoinduced electron transfer (PET) from benzimidazole moiety to BODIPY unit causing quenching of fluorescence. Interestingly, when we titrated the nonfluorescent blue 1-F(-) solution with TFA resulted in a significant enhancement of fluorescence intensity (15-fold) because the PET quenching is prevented due to protonation of benzimidazole group. Furthermore, the reversibility and reusability of sensor 1 for the detection of F(-) ion was tested for six cycles indicating the sensor 1 is stable and can be used in reversible manner.

3,5-Diformylboron dipyrromethenes as fluorescent pH sensors.

A series of boron dipyrromethene (BODIPY) dyes containing two aldehyde functional groups at the 3 and 5 positions have been synthesized in low-to-decent yields in two steps. In the first step, the meso-aryl dipyrromethanes were treated with POCl(3) in N,N-dimethylformamide to afford 1,9-diformylated dipyrromethanes. In the second step, the diformylated dipyrromethanes were first in situ oxidized with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and then reacted with BF(3)·OEt(2) to afford 3,5-diformylboron dipyrromethenes. The X-ray structural analysis indicated that the aldehyde groups are involved in intramolecular hydrogen bonding with fluoride atoms, which may be responsible for the stability of the diformylated BODIPY compounds. The presence of two formyl groups significantly alters the electronic properties, which is clearly evident in downfield shifts in the (1)H and (19)F NMR spectra, bathochromic shifts in the absorption and fluorescence spectra, better quantum yields, and increased lifetimes compared to 3,5-unsubstituted BODIPYs. Furthermore, 3,5-diformylboron dipyrromethenes are highly electron-deficient and undergo facile reductions compared to unsubstituted BODIPYs. These compounds exhibit pH-dependent on/off fluorescence and thus act as fluorescent pH sensors.

Sensing Hg(II) in Vitro and in Vivo Using a Benzimidazole Substituted BODIPY

A multisignaling Hg(II) sensor based on a benzimidazole substituted BODIPY framework was designed, which displays excellent selectively toward Hg(II) in vitro and in vivo. Optical and fluorogenic measurements in solution reveal that the sensor can detect mercury ions at submicromolar concentrations, with high specificity. The detection of Hg(II) is associated with a blue-shift in optical spectra and a simultaneous increase in the fluorescence quantum yield of the sensor, which is attributed to a decrease in charge delocalization and inhibition of photoinduced electron transfer upon binding to Hg(II). Using several spectroscopic measurements, it is shown that the binding mechanism involves two sensor molecules, where lone pairs of the benzimidazole nitrogen coordinate to a single mercury ion. The utility of this BODIPY sensor to detect Hg(II) in vivo was demonstrated by fluorescence imaging and spectroscopy of labeled human breast adenocarcinoma cells. While average emission intensity of the sensor over a large number of cells increases with incubated mercury concentrations, spatially resolved fluorescence spectroscopy performed on individual cells reveals clear spectral blue-shifts from a subensemble of sensors, corroborating the detection of Hg(II). Interestingly, the emission spectra at various submicrometer locations within cells exhibited considerable inhomogeneity in the extent of blue-shift, which demonstrates the potential of this sensor to monitor the local (effective) concentration of mercury ions within various subcellular environments.

Synthesis of 3,5-Bis(acrylaldehyde) Boron-dipyrromethene and Application in Detection of Cysteine and Homocysteine in Living Cells

Synthesis, characterization, and spectral and electrochemical properties of 3,5-bis(acrylaldehyde) BODIPY are described. The compound exhibited higher selectivity toward cysteine/homocysteine than toward other amino acids and thiol-containing compounds as shown by absorption and emission titration experiments and by experiments in living cells.

BODIPY based fluorescent chemodosimeter for explosive picric acid in aqueous media and rapid detection in the solid state

A novel fluorescent chemodosimeter, for specific recognition of explosive picric acid over other nitroaromatic compounds, was developed. It was also demonstrated for the first time that the reported chemodosimeter can selectively detect picric acid, both in solution and solid state.

Synthesis, spectral, electrochemical, and anion binding properties of 3,5-bis(dipyrromethanyl) boron-dipyrromethenes.

Four new boron-dipyrromethenes (BODIPYs) containing dipyrromethanyl substituents at 3,5-positions, bis(3,5-dipyrromethanyl) BODIPYs 5-8, were synthesized by treating their corresponding 3,5-diformyl BODIPYs 1-4 with excess pyrrole under mild acid catalyzed reaction conditions. The compounds 5-8 are stable and freely soluble in common organic solvents. One-dimensional, two-dimensional NMR, high resolution mass spectrometry (HRMS), absorption, fluorescence, and electrochemical techniques were used to characterize the compounds. The spectral and electrochemical studies indicated that dipyrromethanyl groups at 3,5-positions of BODIPY are less electron deficient compared to formyl groups at the same positions. The anion binding studies indicated that bis(3,5-dipyrromethanyl) BODIPY compounds containing four pyrrole NH groups showed preferential binding with F(-) ion over other anions, as confirmed by using NMR, fluorescence, and electrochemical studies.

A boron-dipyrrin–mercury(II) complex as a fluorescence turn-on sensor for chloride and applications towards logic gates

Chloride (Cl−) plays an important role in many cellular responses, including control of membrane potential, neurotransmission, regulation of cell volume and charge balance. Due to its physiological relevance, there is a growing need for improved optical sensors that can detect Cl− ions in biological and environmental samples. Herein, we have developed new N-acylhydrazone substituted BODIPY–mercury(II) based fluorescent turn-on sensors 1–Hg2+ and 2–Hg2+, which showed remarkable selectivity and specificity towards Cl− ions under physiological conditions. The new BODIPY compounds 1 and 2 were synthesized by treating their corresponding 3,5-diformyl BODIPYs 3 and 4 with isonicotinohydrazide in one step under simple reaction conditions. Compounds 1 and 2 absorb in 615–650 nm and emit in 625–660 nm regions. BODIPYs 1 and 2 showed exclusive sensing towards Hg2+ and formed 1–Hg2+ and 2–Hg2+ complexes, respectively, which resulted in the quenching of fluorescence. Jobs plot analyses and HR-MS studies supported the formation of 1–Hg2+ and 2–Hg2+ complexes. Complexes 1–Hg2+ and 2–Hg2+ were found to be exclusive fluorescence turn-on sensors for chloride ions. Upon addition of Cl− ions to 1–Hg2+ and 2–Hg2+ complexes, the mercury(II) ions were extracted from the complexes by releasing the free BODIPYs 1 and 2 which reflected in the significant enhancement of fluorescence intensity (22-fold) with a detection limit of 108 nM. The reversibility and reusability of sensors for the detection of Hg2+ and Cl− ions were tested for six cycles. Interestingly, the sensor can be used to construct an IMPLIES logic gate system as demonstrated in this paper. Furthermore, the probe is cell membrane-permeable and can readily be used to detect the intracellular Cl− ions.

3,5-Bis(dithioacetal) meso-aryl BODIPYs: selective chemodosimeters for Hg(II) ions

Boron-dipyrromethenes containing dithioacetal substituents at 3,5-positions, 3,5-bis(dithioacetal) BODIPYs 1 and 2, were synthesized by treating their corresponding 3,5-diformyl BODIPYs 3 and 4 with excess methyl thioglycolate under mild acid catalyzed reaction conditions. The spectral and electrochemical studies indicated that 3,5-bis(dithioacetal) BODIPYs are less electron deficient compared to 3,5-diformyl BODIPYs. Furthermore, dithioacetal functional groups are very useful for binding metal ions and our studies clearly showed that these dyes can act as selective chemodosimetric probes for the recognition of Hg(II) ions over various other metal ions. The sensing phenomenon employs unique and irreversible Hg(II) promoted deprotection of the dithioacetal groups to aldehyde groups which is clearly demonstrated by absorption, fluorescence, HR-MS and NMR studies. Competitive binding experiments demonstrate that BODIPY 1 can specifically detect Hg(II) ions even in the presence of various other metal ions.

Porphyrin Self-Assembled Monolayer as a Copper Diffusion Barrier for Advanced CMOS Technologies

This paper investigates properties of zinc porphyrin self-assembled monolayer (SAM) as a Cu diffusion barrier for advanced back-end complementary metal-oxide-semiconductor technologies. The SAM layers are integrated with various inter-layer dielectrics (ILDs) such as HSQ and black diamond (BD). Monolayer formation on ILDs was studied using X-ray photoelectron spectroscopy, atomic force microscopy, contact angle, FTIR, and UV-Vis techniques. Degradation study of the Cu/ILD and Cu/SAM/ILD systems was performed using stress-induced CV and IV at elevated temperatures. Time-of-flight secondary ion mass spectrometry was employed to establish effectiveness of these films as Cu diffusion barriers. The results indicate that SAM films, in addition to improving the ILDs moisture resistance, may help in thinning down the existing barrier layer thickness on the low-k porous ILDs. Effect of SAM layers on the mechanical properties of BD film was studied using nanoindentation.

Synthesis, X-ray structure, spectral and electrochemical properties of a β-meso covalently linked BODIPY–Ru(II) dipyrrin complex

We synthesized the BODIPY–Ru(II) dipyrrin complex in decent yield by reacting β-dipyrromethanyl substituted BODIPY with [{(η6-C10H14)RuCl(μ-Cl)}2] under simple reaction conditions. The BODIPY–Ru(II) dipyrrin complex was characterized by 1D, 2D, 13C, 11B, 19F NMR, HR-MS, UV-vis, fluorescence and electrochemical techniques. The BODIPY–Ru(II) dipyrrin complex was further characterized by X-ray structure analysis, which showed that the Ru(II)-dipyrrin complex is in perpendicular orientation to the BODIPY plane in the BODIPY–Ru(II) dipyrrin complex. The ruthenium metal ion in the BODIPY–Ru(II) dipyrrin complex is bonded to dipyrrin nitrogens, one chloro group and arene ring (arene = C10H14) in an η6 manner resulting in a hexa coordination geometry around the Ru(II) ion. The absorption and steady-state fluorescence spectra of the BODIPY–Ru(II) dipyrrin complex showed a broad and hypsochromically shifted absorption and emission bands compared to that of β-dipyrromethanyl substituted BODIPY. The electrochemical studies indicated that the BODIPY–Ru(II) dipyrrin complex was easy to reduce compared to β-dipyrromethanyl substituted BODIPY supporting the electron deficient nature of the BODIPY–Ru(II) dipyrrin complex.