Characteristic Evaluation of Gas Chromatography with Different Detectors for Accurate Determination of Sulfur Hexafluoride.

Sulfur hexafluoride (SF6), which survives in the atmosphere for an extremely long period of time, is the most potent greenhouse gas regulated under the Kyoto Protocol. So, the accurate monitoring of atmospheric SF6 plays an important role in the study of the control policies for reducing greenhouse gas emissions. The instruments for SF6 measurement are typically calibrated using certified reference materials. The concentrations of the commercially available SF6 reference materials usually have a broad range, from 1 µmol/mol to 6000 µmol/mol. Some characteristics including sensitivity, linear range, relative standard deviation, and accuracy are crucial for the determination of SF6 in such a broad concentration range. Therefore, the selection of a proper detector for the accurate determination of SF6 with such a broad range is extremely important to establish a gas chromatography (GC) method for developing SF6 reference materials. In this paper, several typical GC methods with different detectors, including a thermal conductivity detector (TCD), a pulsed discharge helium ionization detector (PDHID), and a flame photometric detector (FPD), were carefully established for the accurate determination of SF6 with different concentrations. The results show that an FPD detector has a relatively narrow linearity range, thus a quadratic equation should be established for building a calibration curve. The PDHID and TCD have good linearity with coefficients of 1.0000 in the concentration range of 10-100 µmol/mol (using a PDHID), and 100-1000 µmol/mol (using a TCD), respectively. Further considering the measurement errors of indication results, the PDHID is suitable for SF6 measurement when the concentrations are below 100 µmol/mol, whereas the TCD is suitable for SF6 measurement when the concentrations are over 100 µmol/mol. These results provide useful guidance in choosing an appropriate GC detector for the accurate determination of SF6, which are especially very helpful for developing SF6 reference materials.

Disilane-bridged architectures: an emerging class of molecular materials.

Disilanes are organosilicon compounds that contain saturated Si-Si bonds. The structural characteristics of Si-Si single bonds resemble those of C-C single bonds, but their electronic structure is more similar to that of C[double bond, length as m-dash]C double bonds, as Si-Si bonds have a higher HOMO energy level. These organosilicon compounds feature unique intramolecular σ electron delocalization, low ionization potentials, polarizable electronic structure, and σ-π interaction. It has been demonstrated that the employment of disilane units (Si-Si) is a versatile and effective approach for finely adjusting the photophysical properties of organic materials in both solution and solid states. In this review, we present and discuss the structure, properties, and relationships of novel σ-π-conjugated hybrid architectures with saturated Si-Si σ bonds. The application of disilane-bridged σ-conjugated compounds as optoelectronic materials, multifunctional solid-state emitters, CPL, and non-linear optical and stimuli-responsive materials is also reviewed.

Novel organoboron complexes with robust core: Synthesis, functionalization, and subcellular targeting.

The construction of novel organoboron complexes with facile synthesis and unique advantages for biological imaging remains a challenge and thus has garnered considerable attention. Herein, we developed a new molecular platform, boron indolin-3-one-pyrrol (BOIN3OPY) via a two-step sequential reaction. The molecular core is robust enough to allow for post-functionalization to produce versatile dyes. When compared to the standard BODIPY, these dyes feature an N,O-bidentate seven-membered ring center, significantly redshifted absorption, and a larger Stokes shift. This study establishes a new molecular platform that provides more flexibility for the functional regulation of dyes.

Si-Bridged annulated BODIPYs: synthesis, unique structure and photophysical properties.

Two novel Si-bridged meso-annulated BODIPY dyes have been prepared through intermolecular C-I silylation and subsequent intramolecular C-H silylation in a one-pot reaction. A marked redshift of the main spectral bands was observed since the efficient σ*-π* conjugation results in a notable stabilization of the LUMOs. Si-annulation blocks the non-radiative decay and contributes to higher fluorescence quantum yields. This strategy is very attractive for the construction of highly emissive polycyclic aromatic hydrocarbons.

Rationalizing the effect of benzo-fusion at [a] and [b] positions of BODIPY on fluorescence yields.

The origin of the large difference of fluorescence yields between benzo[a] and benzo[b] BODIPY derivatives was investigated. The benzo[a]-BODIPY chromophore shows high fluorescence yields while the totally quenched fluorescence of benzo[b]-BODIPYs is observed. Quantum calculations indicated that larger spin-orbit coupling (SOC) and smaller singlet-triplet energy gaps result in non-fluorescence for benzo[b]-BODIPY. Benzo[b]-fusion makes a partial contribution to the HOMO but a full contribution to the HOMO-1, and thus the S1→ S0 and T2→ S0 transitions, involved in HOMO-LUMO and HOMO-1-LUMO, have different characteristics, which leads to spin flipping for intersystem crossing (ISC) and increases the SOC to 1.70 cm-1. However, benzo[a] contributes to HOMO and HOMO-1 equally, and minimizes the SOC between S1 and T2, leading to slow ISC from S1, thus possessing strong fluorescence. These results are useful for the rational design of heavy-atom-free triplet organic chromophores.

Nonsymmetric Benzo[a]fused and Thiophene/Thieno[3,2-b]thiophene[b]fused BODIPYs: Synthesis and Photophysical Properties.

The fusion of sufficient-electron heterocycle rings into the[a]/[b]-position of the BODIPY core would result in a large redshift wavelength, thus achieving red or near infrared emission. In this paper, we described the synthesis of nonsymmetric benzo[a]fused and thiophene/thieno[3,2-b]thiophene[b]fused BODIPY derivatives 2-3 while containing a reactive site, and then, 4-7 were developed by nucleophilic substitution reactions of 3 with various nucleophilic agents in high yields. X-ray crystallographic analysis of 2-7 revealed that the core structure adopted a planar geometry and π-π interactions were observed in the packing structure. BODIPYs 4 and 6-7 displayed a hypochromic shift in the absorption and bathochromic shift in the emission with increasing solvent polarity because of the formation of resonance structures resulting from the change of the C-N distance, which was rationalized by density functional theory (DFT)/time-dependent-DFT calculations.

Oligosilanyl-Bridged Biscarbazoles: Structure, Synthesis, and Spectroscopic Properties.

Oligosilanyl-bridged systems are expected to give rise to unique optoelectronic properties because of σ-π conjugation between the Si-Si σ orbital and the aryl π orbital. Herein, we synthesized a small series of novel biscarbazoles bridged with permethylated oligosilanyl units (-[Si(CH3)2]n-, n = 1-4) and examined their spectroscopic properties in detail. In the target molecules BCzSin , n = 2-4, the efficient σ-π conjugation elevated the highest occupied molecular orbital energy level with no influence on the lowest unoccupied molecular orbital. In the solid state, the emission full width at half-maximum (fwhm) of all the compounds narrowed significantly, while the emission efficiency increased and the emission color of carbazole was retained. This research provided a very simple and general way of subtly manipulating the electronic properties of organic materials to construct an emissive color-retaining system for multifunctional applications.

A General Strategy for the Construction of NIR-emitting Si-rhodamines and Their Application for Mitochondrial Temperature Visualization.

Si-rhodamine (SiR) is an ideal fluorophore because it possesses bright emission in the NIR region and can be implemented flexibly in living cells. Currently, several promising approaches for synthesizing SiR are being developed. However, challenges remain in the construction of SiR containing functional groups for bioimaging application. Herein, we introduce a general and simple approach by a condensation reaction of diarylsilylether and arylaldehyde in o-dichlorobenzene to synthesize a series of SiRs bearing various functional substituents. These SiRs have moderate to high quantum efficiency, tolerance to photobleaching, and high water solubility as well as NIR emitting, and their NIR fluorescence properties can be controlled through the photoinduced electron transfer (PET) mechanism. Fluorescence OFF-ON switching effect is observed for SiR 9 in the presence of acid, which is rationalized by DFT/TDDFT calculations. Moreover, reversible stimuli response toward temperature is achieved. Since positive charge enables mitochondrial targeting ability and chloromethyl unit can covalently immobilize the dyes onto the mitochondrial via click reaction between the benzyl choride and protein sulfhydryls, SiR 8 is identified as a valuable fluorescent marker to visualize the morphology and monitor the temperature change of mitochondria with high photostability.

Real-time monitoring of newly acidified organelles during autophagy enabled by reaction-based BODIPY dyes.

Real-time monitoring of newly acidified organelles during autophagy in living cells is highly desirable for a better understanding of intracellular degradative processes. Herein, we describe a reaction-based boron dipyrromethene (BODIPY) dye containing strongly electron-withdrawing diethyl 2-cyanoacrylate groups at the α-positions. The probe exhibits intense red fluorescence in acidic organelles or the acidified cytosol while exhibiting negligible fluorescence in other regions of the cell. The underlying mechanism is a nucleophilic reaction at the central meso-carbon of the indacene core, resulting in the loss of π-conjugation entailed by dramatic spectroscopic changes of more than 200 nm between its colorless, non-fluorescent leuco-BODIPY form and its red and brightly emitting form. The reversible transformation between red fluorescent BODIPY and leuco-BODIPY along with negligible cytotoxicity qualifies such dyes for rapid and direct intracellular lysosome imaging and cytosolic acidosis detection simultaneously without any washing step, enabling the real-time monitoring of newly acidified organelles during autophagy.

Lysosome-targeting turn-on red/NIR BODIPY probes for imaging hypoxic cells.

A small series of fluorescent lysosome-targeting probes based on the BODIPY fluorophore and containing morpholine and nitro groups were rationally designed. These probes emitted light from green to NIR wavelengths, and provided specificity for imaging the lysosomes of hypoxic cells. The electron-withdrawing nitrophenyl group at the meso position was found to lead to highly efficient nonradiative decay of the S1 state, and hence a recovery of fluorescence when reduction of the nitro group occurred under hypoxic conditions.

Thieno[3,2-b]thiophene fused BODIPYs: synthesis, near-infrared luminescence and photosensitive properties.

The fusion of π-sufficient heteroaryl moieties has proven to be an effective strategy for achieving the red shift of the main spectral bands of BODIPY. In this paper, thieno[3,2-b]thiophene-fused BODIPY derivatives 1 and 2 have been designed and characterized by various spectroscopic methods, and their photosensitive properties have also been explored. Both dyes absorb in the near-infrared region with extremely high molar extinction coefficients, due to the extension of π-conjugation by fusion of the thieno[3,2-b]thiophene moiety. Their fluorescence quantum yields and singlet oxygen generation properties are significantly affected by iodine substitutions; dye 2 displays a moderate singlet oxygen generation value of 0.32, which makes it a potential NIR photosensitizer for photodynamic therapy of cancer in future research.

A mononuclear five-coordinate Co(ii) single molecule magnet with a spin crossover between the S = 1/2 and 3/2 states.

Although a great number of single-ion magnets (SIMs) and spin-crossover (SCO) compounds have been discovered, multifunctional materials with the combination of SCO and SIM properties are extremely scarce. Here magnetic studies have been carried out for a mononuclear, five-coordinate cobalt(ii) complex [Co(3,4-lut)4Br]Br (1) with square pyramidal geometry. Direct-current magnetic measurement confirms the spin transition between the S = 1/2 and 3/2 states in the range of 150-290 K with a small hysteresis loop. Frequency- and temperature-dependent alternating-current magnetic susceptibility reveals slow magnetization relaxation under an applied dc field of 3000 Oe. The work here presents the first instance of the five-coordinate mononuclear cobalt(ii)-based SIM exhibiting the thermally induced complete SCO.

Naphtho[b]-fused BODIPYs: one pot Suzuki-Miyaura-Knoevenagel synthesis and photophysical properties.

Naphtho[b]-fused BODIPYs have been facilely synthesized via Suzuki-Miyaura-Knoevenagel reaction between mono-iodo-BODIPY or 2,6-diiodo-BODIPY with (2-formylphenyl)boronic acid. This one-pot reaction represents a very straightforward approach for tuning the absorption and emission of BODIPYs in the red visible/NIR range.

Rational Design of Emissive NIR-Absorbing Chromophores: Rh(III) Porphyrin-Aza-BODIPY Conjugates with Orthogonal Metal-Carbon Bonds.

The facile synthesis of Group 9 Rh(III) porphyrin-aza-BODIPY conjugates that are linked through an orthogonal Rh-C(aryl) bond is reported. The conjugates combine the advantages of the near-IR (NIR) absorption and intense fluorescence of aza-BODIPY dyes with the long-lived triplet states of transition metal rhodium porphyrins. Only one emission peak centered at about 720 nm is observed, irrespective of the excitation wavelength, demonstrating that the conjugates act as unique molecules rather than as dyads. The generation of a locally excited (LE) state with intramolecular charge-transfer (ICT) character has been demonstrated by solvatochromic effects in the photophysical properties, singlet oxygen quantum yields in polar solvents, and by the results of density functional theory (DFT) calculations. In nonpolar solvents, the Rh(III) conjugates exhibit strong aza-BODIPY-centered fluorescence at around 720 nm (ΦF =17-34 %), and negligible singlet oxygen generation. In polar solvents, enhancements of the singlet-oxygen quantum yield (ΦΔ =19-27 %, λex =690 nm) have been observed. Nanosecond pulsed time-resolved absorption spectroscopy confirms that relatively long-lived triplet excited states are formed. The synthetic methodology outlined herein provides a useful strategy for the assembly of functional materials that are highly desirable for a wide range of applications in material science and biomedical fields.

User-friendly aerobic reductive alkylation of iridium(III) porphyrin chloride with potassium hydroxide: scope and mechanism.

Alkylation of iridium 5,10,15,20-tetrakistolylporphyrinato carbonyl chloride, Ir(ttp)Cl(CO) (1), with 1°, 2° alkyl halides was achieved to give (ttp)Ir-alkyls in good yields under air and water compatible conditions by utilizing KOH as the cheap reducing agent. The reaction rate followed the order: RCl < RBr < RI (R = alkyl), and suggests an SN2 pathway by [Ir(I)(ttp)](-). Ir(ttp)-adamantyl was obtained under N2 when 1-bromoadamantane was utilized, which could only undergo bromine atom transfer pathway. Mechanistic investigations reveal a substrate dependent pathway of SN2 or halogen atom transfer.

Asymmetric core-expanded aza-BODIPY analogues: facile synthesis and optical properties.

Significantly large Stokes shifts and enhanced solid state emissions were achieved in a novel series of asymmetric core-expanded aza-BODIPY analogues, 4a-4d, synthesized by a facile and scalable two-step reaction in high yields.

Core-modified rubyrins containing dithienylethene moieties.

Two stable core-modified rubyrins bearing one and two dithienylethene (DTE) units (1 and 2) have been synthesized. With one "closed-form" DTE unit, 1 shows aromaticity associated with its conjugated circuit of 26 π-electrons. In contrast, rubyrin 2 containing one "open-form" DTE unit has nonaromatic properties.

Thienopyrrole-expanded BODIPY as a potential NIR photosensitizer for photodynamic therapy.

The synthesis and characterization of a highly photostable bromo-substituted BODIPY dye (I) fused-ring-expanded with thienopyrrole moieties is reported. The results of MTT assays and flow cytometric analyses in living HeLa cells demonstrate that I has a high singlet oxygen quantum yield (ΦΔ = 0.63) and exhibits photocytotoxicity upon irradiation in the NIR region making it potentially suitable for use in PDT.

Enhancing the Stokes' shift of BODIPY dyes via through-bond energy transfer and its application for Fe(3+)-detection in live cell imaging.

Two energy transfer cassettes that exhibit a large pseudo Stokes' shift (up to 400 nm) due to efficient through-bond energy transfer (up to 99%) have been constructed. Selective binding of Fe(III) with the donor entity significantly suppresses the excitation energy transfer resulting in fluorescence quenching in aqueous solution and in living cells.