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Two thia-heterohelicenes of different length, namely a hetero [4]-helicene ( 1 ), and a hetero [6]-helicene ( 2 ) are studied by electronic circular dichroism (ECD), circularly polarized luminescence (CPL), vibrational circular dichroism (VCD) and optical rotation (OR). It is found that the ECD and VCD spectra are characteristically different from the corresponding spectra of the parent helicene molecules, indicative of the presence of hetero atoms. CPL spectra are discussed on the basis of DFT calculation results. The sign of the OR is different for the two thiaheterohelicenes and is correctly predicted by DFT calculations. [ABSTRACT FROM AUTHOR]

We review the present status of experiments and calculations for circularly polarized luminescence (CPL) of simple organic molecules and of stimuli-responsive organic molecules. Together with the historical report of the main instrumental approaches, a few crucial points about experiments are tackled, with the aim of defining measurement protocols, in view of the wide availability of commercial apparatuses in the near future. The calculations aimed at interpreting the CPL spectra, mostly based on time-dependent Density Functional Theory (TD-DFT) calculations, which started around 2010, are reviewed, limiting the discussion to small to mid-sized molecules. Some applications of CPL spectra of organic molecules-based systems are presented, with a focus especially on two fields: material science and biology. Chirality 28:696-707, 2016. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

ABSTRACT UV, circular dichroism (CD), fluorescence and circularly polarized luminescence (CPL) spectra were recorded for a set of four related [2.2.1] bicyclic compounds ((1 S,4 S)-and (1 R,4 R)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-one, namely (1 S)- and (1 R)-camphor ( 1), (1 S,4 R)-4,7,7-trimethylbicyclo[2.2.1]hept-5-en-2-one, (1 S)-dehydro-epicamphor ( 2), (1 S,4 S)-1,7,7-trimethylbicyclo[2.2.1]heptane-2,5-dione, (1 S)-5-oxocamphor ( 3), (1 S,4 R)- and (1 R,4 S)-1,7,7-trimethylbicyclo[2.2.1]heptane-2,3-dione, (1 S)- and (1 R)-camphorquinone ( 4)) and a set of three related [2.2.2] bicyclic compounds (1 S,4 S)-bicyclo[2.2.2]octan-2,5-dione (saturated diketone ( 5)), (1 R,4 R)-bicyclo[2.2.2]oct-7-en-2,5-dione (unsaturated diketone ( 6)), ((1 S,4 S)-bicyclo[2.2.2]oct-7-en-5( S)-ol-2-one (which we refer to as unsaturated hydroxy-ketone ( 7)). For the latter three compounds also mid-IR vibrational circular dichroism (VCD) spectra were recorded and are presented. Time-Dependent Density Functional (TD-DFT) calculations provide a satisfactory interpretation of both absorption and emission chiroptical spectra and permit insight into ground and excited state electronic properties. We discuss the applicability of the octant rule or of other approximated models to rationalize the observed sign of the CPL. Chirality 25:589-599, 2013. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

ABSTRACT Ultraviolet (UV), Circular Dichroism (CD), Fluorescence, and Circularly Polarized Luminescence (CPL) spectra were recorded for mixed chloroform/methanol and chloroform/butanol solutions of regioregular poly[3-(( S)-2-methylbutyl)-thiophene]. An evaluation of the chiral and nonchiral components in solution is proposed on the basis of the UV and CD spectra. The fluorescence and CPL spectra are observed in a wavelength range where some UV and CD activity still appears. For this reason, the observed CPL features are strongly influenced by CD. A general procedure for evaluating true CPL spectra is proposed, when absorption and emission coexist. Chirality 24:725-730, 2012. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Among the various chiroptical spectroscopic techniques available today, circularly polarized luminescence (CPL) plays a minor role and is still used by a limited number of specialists. The cost of the few commercial instruments available and the complexity of homemade apparatuses have strongly limited the widespread application of this technique. New technological approaches, such as the use of light-emitting diode (LED) sources, may significantly simplify the required instrumentation and encourage new potential users. Calibration procedure and the quantitative determination of CPL and total luminescence intensity as well as the corresponding gratio are described. [ABSTRACT FROM AUTHOR]

Almost all Iridium(III) complexes employed both as dopants in PhOLEDs and as pharmaceuticals and fluorescence bioprobes are racemic mixtures. In this study the single enantiomers of the most stable diastereomeric form fac-trans-N–N , bis[2-(4,6-difluorophenyl)pyridinato-C 2 , N ](picolinato)iridium(III) (FIrpic) were separated and analysed. The data obtained showed that the complex can be separated into stable optically active Λ and Δ isomers employing cellulose based chiral stationary phase both in normal and polar phase mode. Their chirality was confirmed and their absolute configuration assigned employing several methods (DFT and TDDFT calculations, CD and VCD). The CPL spectroscopy of the isolated enantiomers of FIrpic was also recorded due to its possible value in the OLEDs field. The chromatographic method was applied for a semipreparative purpose demonstrating that polar organic solvent chromatography (POSC) could be used to avoid the low-solubility issues associated with these Iridium(III) complexes. Finally, the chemical and stereochemical stability of the single isomers was evaluated under thermal stress by liquid chromatography coupled to high-resolution mass spectrometry (LC-QTOF) on both chiral and achiral columns. No racemization and/or isomerization was observed; however, the dissociation of the ancillary ligand was demonstrated employing LC-QTOF. [ABSTRACT FROM AUTHOR]

Diesters of (1R,2R)- and (1S,2S)-cyclohexanediols and diamides of (1R,2R)- and (1S,2S)-diaminocyclohexane with p-hydroxycinnamic acid have been known for some time to exhibit intense bisignate electronic circular dichroism (ECD) spectra in CH3OH. It was also known that added NaOH causes a bathochromic shift of ~50 nm in CH3OH, and an even higher one in DMSO. We have measured vibrational circular dichroism (VCD) spectra both for neutral compounds and in the presence of NaOH and other bases. The VCD and IR spectra in the mid-IR region for CD3OD and DMSO-d6 solution exhibit high sensitivity to the charged state for the diesters. They possess two strong bisignate features in the presence of bases in the mid-IR, which are interpreted in terms of vibrational exciton couplets, while this phenomenon is less evident in diamides. VCD allied to density functional theory (DFT) calculations allows one to shed some light on the spectral differences of diesters and diamides by studying their conformational properties. Optical rotatory dispersion (ORD) curves confirm the ECD data. Circularly polarized luminescence (CPL) data have been also acquired, which are rather intense in basified solution: the CPL spectra are monosignate and are as intense in the diester and in the diamide case. [ABSTRACT FROM AUTHOR]

Vibrational circular dichroism spectra (VCD) in the mid-IR region and electronic circular dichroism (ECD) spectra for three carnitine derivatives in the form of hydrochloride salts were recorded in deuterated methanol solutions. Density Functional Theory calculations help one to understand the significance of the observed VCD bands. VCD and ECD spectra are informative about the absolute configuration of the molecule, but VCD data reveal also some conformational aspects in the N, N, N-trimethyl moiety and inform us about interactions gained from the carbonyl stretching region for the acyl substituted carnitines. Chirality 27:907-913, 2015. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

A new chiral diketonate ligand based on carvone binds early lanthanides. The Eu complex displays high circularly polarized (glum = 0.82) red luminescence under near-UV excitation in the solid state. This is the first report on such CPL activity in the solid state with a rigorous protocol to exclude artifacts. Paramagnetic NMR spectroscopy revealed the nature and structure of the active species. [ABSTRACT FROM AUTHOR]

A complete chiroptical characterization of the supramolecular polymers formed by tricarboxamides (S)-1 and (R)-1 is performed using ECD, VCD and CPL dichroic techniques. The helical aggregates show an intense CPL signal and their absolute P- or M-configuration is assigned with the help of theoretical calculations. [ABSTRACT FROM AUTHOR]

Linear conjugated oligothiophenes of variable length and different substitution pattern are ubiquitous in technologically advanced optoelectronic devices, though limitations in application derive from insolubility, scarce processability and chain-end effects. This study describes an easy access to chiral cyclic oligothiophenes constituted by 12 and 18 fully conjugated thiophene units. Chemical oxidation of an 'inherently chiral' sexithiophene monomer, synthesized in two steps from commercially available materials, induces the formation of an elliptical dimer and a triangular trimer endowed with electrosensitive cavities of different tunable sizes. Combination of chirality with electroactivity makes these molecules unique in the current oligothiophenes literature. These macrocycles, which are stable and soluble in most organic solvents, show outstanding chiroptical properties, high circularly polarized luminescence effects and an exceptional enantiorecognition ability. [ABSTRACT FROM AUTHOR]

Circular dichroism (CD) spectra at variable temperatures have been recorded for human cytosolic sialidase NEU2 in buffered water solutions and in the presence of divalent cations. The results show the prevalence of β-strands together with a considerable amount of α-helical structure, while in the solid state, from both previous X-ray diffraction analysis and our CD data on film samples, the content of β-strands is higher. In solution, a significant change in CD spectra occurs with an increase in temperature, related to a decrease in cr-helix content and a slight increase in β-strand content. In the same range of temperatures, the enzymatic activity decreases. Although the overall structure of the protein appears to be particularly stable, molecular dynamics simulations performed at various temperatures evidence local conformational changes possibly relevant for explaining the relative lability of enzymatic activity. [ABSTRACT FROM AUTHOR]

Upon slow evaporation of a 1:1 diastereoisomeric mixture of Boc-(L-Phe-L-Oxd)2-OBn (1; Boc=tert-butyloxycarbonyl; L-Oxd=trans-(4S,5R)-4-carboxy 5-methyloxazolidin-2-one, Bn= benzyloxycarbonyl) and Boc-L-Phe-L-Oxd-d-Phe-L-Oxd-OBn (2) in methyl tert-butyl ether, single crystals suitable for an X-ray diffraction study were obtained. In contrast, the two pure oligomers lead to the formation of amorphous solids under any crystallization conditions. The preferential conformation of both oligomers was fully elucidated in the solid phase and compared with the known conformation of Boc-(L-Phe-d-Oxd)2-OBn (3). The preferred conformation of 1 ranges from a polyproline II (PPII) helix to β strands and we can gather that longer and more structured oligomers will form PPII helices. In contrast, compound 3 forms infinite antiparallel b-sheet structures; thus showing the strong effect of the reversal of the absolute configuration of the Oxd moieties on the secondary structure of these hybrid foldamers. The same outcome was retained in solution, as demonstrated by vibrational circular dichroism analysis. Finally, we have demonstrated that a 1:1 mixture of 1 and 2 leads to the formation of new materials with interesting properties that are missing from the two pure compounds, such as the tendency to form crystals, fibers, and globules, depending on the solvent. [ABSTRACT FROM AUTHOR]

Abstract: 1,3-Dioxolane- and dioxane-type (1- and 2-naphthyl)ethylidene ketals of p-methoxyphenyl α-l-rhamnopyranoside and β-d-glucopyranoside were prepared and their stereochemistry studied by solution and solid-state circular dichroism, X-ray diffraction, and coupled-oscillator CD calculations on the solid-state and MMFF-calculated geometries. Intermolecular exciton-coupled interactions between the nearby aromatic chromophores in the solid state and different conformers in solution and solid state could be identified as the main reason for the difference between solution and solid-state CDs. [Copyright &y& Elsevier]

Invited for the cover of this issue is Francesco Sannicolò and co-workers at different Italian institutions, who all contributed to the different specific areas of this multidisciplinary work. The image depicts inherently chiral elliptical and triangular oligothiophene macrocycles and their symmetrical resemblance to mysterious crop circles. Read the full text of the article at . [ABSTRACT FROM AUTHOR]

When new topologically appealing molecules are formed, fantasy ‐ assisted cogitation tries to associate their shapes to objects of everyday life: knots, cylinders, pretzels, baskets, ladders, etc. Chirality adds a touch of intelligence to these molecules, which gain the ability to recognize enantiomorphic species. In their Communication on page 15298 ff., F. Sannicolò et al. describe some inherently chiral elliptical and triangular oligothiophene macrocycles which they associate with the pictograms of some more or less mysterious crop circles. Photograph courtesy of Mr. Steve Alexander, www.temporarytemples.co.uk. [ABSTRACT FROM AUTHOR]