Optical resolution of the hyperfine structure of the Na D lines by atomic beam absorption from a cw tunable dye laser

An optical spectroscopic experiment, allowing a resolution of at least 20 MHz, is described. A cw tunable dye laser with very high frequency stability is used in conjunction with a Rabi type sodium atomic beam. The experimental linewidth was only limited by the natural width of the sodium resonance lines. The hyperfine structure of the 3²P_{$\text{3}\text{2}$} state of sodium has been resolved, for the first time with a purely optical technique.     

Achieving high circularly polarized luminescence with push–pull helicenic systems: from rationalized design to top-emission CP-OLED applications

While the development of chiral molecules displaying circularly polarized luminescence (CPL) has received considerable attention, the corresponding CPL intensity, g_lum, hardly exceeds 10⁻² at the molecular level owing to the difficulty in optimizing the key parameters governing such a luminescence process. To address this challenge, we report here the synthesis and chiroptical properties of a new family of π-helical push–pull systems based on carbo[6]helicene, where the latter acts as either a chiral electron acceptor or a donor unit. This comprehensive experimental and theoretical investigation shows that the magnitude and relative orientation of the electric (μ_e) and magnetic (μ_m) dipole transition moments can be tuned efficiently with regard to the molecular chiroptical properties, which results in high g_lum values, i.e. up to 3–4 × 10⁻². Our investigations revealed that the optimized mutual orientation of the electric and magnetic dipoles in the excited state is a crucial parameter to achieve intense helicene-mediated exciton coupling, which is a major contributor to the obtained strong CPL. Finally, top-emission CP-OLEDs were fabricated through vapor deposition, which afforded a promising g_El of around 8 × 10⁻³. These results bring about further molecular design guidelines to reach high CPL intensity and offer new insights into the development of innovative CP-OLED architectures.

A CPL intensity of up to 3 × 10⁻² is achieved in π-extended 6-helicene derivatives, owing to an intense helicene-mediated exciton coupling. Corresponding top-emission CP-OLEDs afforded a promising g_El of around 8 × 10⁻³.

The design of chiral emitters displaying intense circularly polarized luminescence (CPL) has attracted significant interest, thanks to the potential of CP light in a diverse range of applications going from chiroptoelectronics (organic light-emitting diodes (OLEDs), optical information processing, etc.) to bio-imaging and chiral sensing.¹ Recently, designing OLEDs with CP electroluminescence (CP-OLEDs) has emerged as an interesting approach to improve high-resolution display performance. Namely, using unpolarised OLEDs, up to 50% of the emitted light can be lost due to the use of antiglare polarized filters.² In CP-OLEDs, the electro-generated light can pass these filters with less attenuation owing to its circular polarization and thus lead to an increase of the image brightness with lower power consumption.³ To develop CP-OLED devices, the main approach relies on the doping of the device''s emitting layer by a CPL emitter, which should ensure simultaneously high exciton conversion and a high degree of circular polarization. The harvesting of both singlet and triplet excitons has been successfully addressed using either chiral phosphorescent materials or thermally activated delayed fluorescence (CP-TADF) emitters with device efficiencies of up to 32%.⁴ However, the intensity of circularly polarized electroluminescence (CPEL), evaluated by the corresponding dissymmetry factor g_El, remains inefficient and typically falls within the range of 10⁻³ with limited examples reaching g_El > 10⁻² based on polymeric materials and lanthanide complexes.⁵ For CP-OLEDs using a molecular chiral emissive dopant, g_El, defined as the ratio between the intensity difference of left- and right-CPEL, and the total generated electroluminescence, 2(El_L − El_R)/(El_L + El_R), can be generally related to the luminescence dissymmetry factor g_lum measured in diluted solution.² Accordingly, it is of crucial importance to design luminescent molecules with high g_lum values,^3,28a–d,29 in order to reach strong CP electro-luminescence when going to practical devices. However, structural and electronic factors that govern the CPL of chiral compounds are still poorly understood even if a few studies have recently tried to rationalize and establish molecular guidelines to obtain high g_lum values.⁶Our team has contributed to the research in this area by developing extended π-helical molecular architectures resulting from the association of carbo[6]helicene and achiral dyes,⁷ which afforded enhanced chiroptical properties, with notably a g_lum up to 10⁻², owing to an uncommon chiral exciton coupling process mediated by the chiral helicenic unit.⁸ In addition, we also described an unusual solvent effect on the intensity of CPL of π-helical push–pull helicene–naphthalimide derivatives,^7b which showed a decrease of g_lum from 10⁻² to 10⁻³ upon increasing the polarity of solvent.^7b This solvatochromism effect was shown to be related to a symmetry breaking of the chiral excited state before emission,⁹ which modifies the relative intensity of the magnetic (μ_m) and electric (μ_e) dipole transition moments, and the angle, θ, between them (Fig. 1), ultimately impacting g_lum. The latter is well approximated as 4|m|cos θ/(|μ|) for an electric dipole-allowed transition.¹⁰Open in a separate windowFig. 1Chemical structures of “push–pull” 2,15-diethynylhexahelicene-based emitters with their polarized luminescence characteristics including their calculated electric and magnetic transition dipole moments and the angle between them corresponding to the S₁ → S₀ transition.While these results highlight interesting aspects regarding the key parameters influencing the CPL of organic emitters, this type of “helical push–pull design” remains limited to only one example, which render the systematic rationalization of these findings difficult. Accordingly, we decided to develop a complete family of new chiral push–pull compounds to explore the structural and electronic impact of the grafted substituents on the helical π-conjugated system. In addition, we went a step further and incorporated the designed chiral emitter into proof-of-concept CP-OLEDs using a top-emission architecture,¹¹ which remains scarcely explored for CP-light generation despite its considerable potential for micro-display applications. To the best of our knowledge, only one example of such type of electroluminescent device has been reported, using a CP-TADF emitter, affording a modest g_El of 10⁻³.^11aHerein, we report the synthesis and chiroptical properties of a new family of π-helical push–pull systems based on chiral carbo[6]helicene, functionalized by either electron donor or acceptor units. Interestingly, the chiral π-conjugated system of the helicene may act as either an electron acceptor or a donor, depending on the nature of the attached substituents, thereby impacting the chiroptical properties, notably the resulting CPL. By optimizing the chiral exciton coupling process through the modulation of the magnitude and relative orientation of the electric (μ) and magnetic (m) dipoles, the chiroptical properties of classical carbo[6]helicene-based emitters can be dramatically enhanced and reach high g_lum values at the molecular level, i.e. up to 3–4 × 10⁻². Experimental and theoretical investigations revealed that the mutual orientation of the electric and magnetic dipoles in the excited-state is a crucial parameter and is optimal when the substituents attached to the helicene core possess a rather weak electron withdrawing or donating ability. Finally, proof of concept top-emission CP-OLEDs were fabricated through vapor deposition of π-helical push–pull derivatives and afforded a g_El of around 8 × 10⁻³, which represents a significant improvement for the polarization of electroluminescence emitted using this device architecture.     

Synthesis and crystal structure of IM-6, a new open framework cobalt-gallium phosphate with ten- and twelve-membered pore openings

A new three-dimensional microporous cobalt-gallium phosphate, named IM-6, has been synthesized under solvothermal conditions with an N-substituted piperazine as organic template. The structure was solved by single-crystal X-ray diffraction (triclinic, P(-)1, a=9.848(20), b=12.470(32), c=12.603(28)A, alpha=63.47(16) degrees, beta=74.56(16) degrees, gamma=76.03(17) degrees). IM-6 exhibits a new framework topology. The inorganic framework is built up of MO(4) (M=Co, Ga) and PO(4) tetrahedra. It displays a two-dimensional interconnected channel system running along the [0(-)11] and [100] directions and delimited by ten- and twelve-membered ring openings, respectively.     

Carbanion substituent effects on 1-disubstituted 4-(4'-pyridyl)pyridinium methylide structures using 13C NMR spectroscopy and DFT method

The structure of 1-disubstituted 4-(4'-pyridyl)pyridinium methylides or 4,4'-bipyridinium monoylides (2-5) with a wide range of carbanion substituents, were determined using 13C NMR signals in dimethylsufoxide (DMSO-d(6)) solution. For the first time, we developed a systematic determination of 13C NMR chemical shifts of the ylidic carbon using a long-range correlated (1H-(13)C) HMBC experiments. The chemical shift values are discussed in terms of magnetic and/or electronic effects of the ylidic carbon substituents. From the extracted NMR parameters and the results of accompanying quantum chemical DFT calculations for a three-dimensional (3D)-structure representation, we found a long distance electronic effect where the aromatic heterocycle C2z.sbnd;C6 and C4 centers are perturbed according to the electron acceptor strengths of ylidic carbon substituents in all monoylides (2-5c) capable to stabilize in a planar conformation. No significant perturbation on C2z.sbnd;C6 and C4 centers are found in all other monoylides (2-5a, b) that adopted a non-planar conformation. Good similar linear dependences of the chemical shift variation Delta (calculated by the differences of analogous C2z.sbnd;C6 and C4 chemical shifts in non-planar and planar monoylides) with the ylidic carbon chemical shifts modulated by the strength of electron acceptor substituents pointed out the resonance interaction or the delocalization phenomena of the ylidic carbon charge on the heterocycle.     

MTD-PLS: a PLS variant of the minimal topologic difference method. III. Mapping interactions between estradiol derivatives and the alpha estrogenic receptor

A homogeneous collection of 45 estrogen agonist derivatives with relative binding affinities measured to the estrogen receptor from Ratus norvegicus was used. The quantitative structure-activity relationships were derived using an improved minimal topologic difference (MTD) method in a partial least-squares (PLS) variant. The spatially assigned analysis of fragment properties can provide receptor site maps, within the limits of the existing series. A steric misfit was found for the steroidal position 2; benefic hydrophobic and van der Waals (enhanced by high polarizability) interactions were found for the 17alpha-CH=CH-X group. MTD-PLS mapping results are confirmed by the experimentally derived estradiol-estrogen receptor binding site contacts (based on X-ray crystallography). Our results suggest that this MTD-PLS method can yield useful results for interactions with receptors of unknown 3D structure and, generally, for the steric rigidity of receptor sites.     

Synthesis of dihydronaphthalenes via aryne Diels-Alder reactions: scope and diastereoselectivity

Novel aryne Diels-Alder reactions with functionalized acyclic dienes are reported. These give useful cis-substituted dihydronaphthalene building blocks in good yield which are not easily accessible via other means, as demonstrated in the synthesis of sertraline. The first asymmetric aryne cycloaddition with an acyclic diene is also reported, giving excellent diastereoselectivities with Oppolzer's sultam as a chiral auxiliary.     

Indirect detection of photosensitizer ex vivo

Photodynamic therapy induces the production of reactive oxygen species (ROS) within tissues exposed to laser light after administration of a sensitizer. In the context of continuing clinical and commercial development of chemicals with sensitizing properties, a minimally invasive assay is needed to determine the tissue kinetics of fluorescent or non-fluorescent photoreactive drugs. The level of ROS was determined ex vivo from 1 mm3 biopsy samples using 2'-7' dichlorofluorescin diacetate (DCFH-DA), a fluorescent probe which was converted into highly fluorescent dichlorofluorescein (DCF) in the presence of ROS. This assay was tested on meta(tetrahydroxyphenyl)chlorin (m-THPC, FOSCAN), a powerful and fluorescent sensitizer, and bacteriochlorophyll derivative WST09 (TOOKAD), a near-infrared absorbing sensitizer that is only slightly fluorescent. In conjunction with the ROS assay, the tissue accumulation of m-THPC was determined on biopsy samples using an optic fibre spectrofluorometer (OFS). DCF fluorescence was proportional to the level of oxidation induced by horseradish peroxidase used as a control and to the concentration (range: 0-5 microg x ml(-1)) of both selected photosensitizers irradiated in a tube together with DCFH. Regardless of the organ studied, an excellent correlation was found between fluorescence measurement by OFS and ROS determination for m-THPC. m-THPC (2 mg x kg(-1) iv) accumulation in tumour tissues was best after 48 h, and the best signal was obtained in liver. With non-fluorescent WST09 (2 mg x kg(-1)), ROS determination showed the best tumour uptake 48 h after injection, with a tumour/muscle ratio of 5.4. The ROS assay appears to be feasible for determining sensitizer concentration in regular grip biopsy tissue samples.     

New tetrapyrazolic macrocycle. Synthesis and preliminary use in metal ion extraction

A new macrocycle containing two bipyrazolic units, with a side-arm bearing an attached donor-group is reported. The complexing properties of this compound towards heavy metal ions (Hg²⁺, Cd²⁺, Pb²⁺) and alkaline metal ions (Ca²⁺, Cs⁺, K⁺, Na⁺, Li⁺) was studied by a liquid-liquid extraction process and the extracted cation percentage was determined by atomic absorption measurements and UV spectroscopy.