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4-[5-(Naphthalen-1-ylmethyl)-1,3,4-thiadiazol-2-yl]benzene-1,3-diol (NTBD) was extensively studied through stationary UV-vis absorption and fluorescence measurements in various solvents and solvent mixtures and by first-principles quantum chemical calculations. It was observed that while in polar solvents (e.g., methanol) only a single emission band emerged; the analyzed 1,3,4-thiadiazole derivative was capable of producing dual fluorescence signals in low polarity solvents (e.g., n -hexane) and certain solvent mixtures (e.g., methanol/water). As clearly follows from the experimental spectroscopic studies and theoretical modeling, the specific emission characteristic of NTBD is triggered by the effect of enol → keto excited-state intramolecular proton transfer (ESIPT) that in the case of solvent mixture is reinforced by aggregation of thiadiazole molecules. Specifically, the restriction of intramolecular rotation (RIR) due to environmental hindrance suppresses the formation of non-emissive twisted intramolecular charge transfer (TICT) excited keto* states. As a result, this particular thiadiazole derivative is capable of simultaneously producing both ESIPT and aggregation-induced emission (AIE).

Optically active functional noncentrosymmetric architectures might be achieved through the combination of molecules with inscribed optical responses and species of dedicated tectonic character. Herein, we present the new series of noncentrosymmetric cocrystal salt solvates (PPh 4 ) 3 [M(CN) 6 ](L) n · m solv (M = Cr(III), Fe(III), Co(III); L = polyresorcinol coformers, multiple hydrogen bond donors: 3,3',5,5'-tetrahydroxy-1,19-biphenyl, DiR, n = 2, or 5'-(3,5-dihydroxyphenyl)-3,3″,5,5″-tetrahydroxy-1,19:3',1″-terphenyl, TriRB, n = 1) denoted as MDiR and MTriRB , respectively. The hydrogen-bonded subnetworks {[M(CN) 6 ] 3- ;L n } ∞ of dmp , neb , or dia topology are formed through structural matching between building blocks within supramolecular cis -bis(chelate)-like {[M(CN) 6 ] 3- ;( H 2 L) 2 ( H } or tris(chelate)-like {[M(CN) 2 } or tris(chelate)-like {[M(CN) 6 ] 3- ;( H 2 L) 3 } fragments. The quantum-chemical analysis demonstrates the mixed electrostatic and covalent character of these interactions, with their strength clearly enhanced due to the negative charge of the hydrogen bond acceptor metal complex. The corresponding interaction energy is also dependent on the geometry of the contact and size matching of its components, rotational degree of freedom and extent of the π-electron system of the coformer, and overall fit to the molecular surroundings. Symmetry of the crystal lattices is correlated with the local symmetry of coformers and {complex;(coformer) n } hydrogen-bonded motifs characterized by the absence of the inversion center and mirror plane. All compounds reveal second-harmonic generation activity and photoluminescence diversified by individual UV-vis spectral characteristics of the components, and interesting low-frequency Raman scattering spectra within the subterahertz spectroscopic domain. Vibrational (infrared/Raman), UV-vis electronic absorption (experimental and calculated), and 57 Fe Mössbauer spectra together with electrospray ionization mass spectrometry (ESI-MS) data are provided for the complete description of our systems.

A series of molecules that possess two quinolines, benzoquinolines, or phenanthrolines connected in a chiral fashion by a biaryl junction along with their water-soluble derivatives was developed and characterized. The influence of the structure on the basicity of the nitrogen atoms in two heterocycles was examined and the photophysical and chiroptical switching activity of the compounds upon protonation was studied both experimentally and computationally. The results demonstrated that changes in the electronic structure of the protonated vs. neutral species, promoting a bathochromic shift of dominant electronic transitions and alternation of their character from π-to-π* to charge-transfer-type, when additionally accompanied by the high structural flexibility of a system, leading to changes in conformational preferences upon proton binding, produce particularly pronounced modifications of the spectral properties in acidic medium. The latter combined with reversibility of the read-out make some of the molecules in this series very promising multifunctional pH probes.

The preparation of the first enantiopure cycloplatinated complexes bearing a bidentate, helicenic N-heterocyclic carbene and a diketonate ancillary ligand is presented, along with their structural and spectroscopic characterization based on both experimental and computational studies. The systems exhibit long-lived circularly polarized phosphorescence in solution and in doped films at room temperature, and also in a frozen glass at 77 K, with dissymmetry factor g lum values ≥10 -3 in the former and around 10 -2 in the latter.

The photophysical and chiroptical properties of a novel, chiral helicene-NHC-Re(I) complex bearing an N-(aza[6]helicenyl)-benzimidazolylidene ligand are described, showing its ability to emit yellow circularly polarized luminescence. A comparative analysis of this new system with other helicene-Re(I) complexes reported to date illustrates the impact of structural modifications on the emissive and absorptive properties., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

2-Amino[2.2]paracyclophane reacts with salicylaldehyde or 2-hydroxyacetophenone to yield imines that then give access to a new series of boranils (8b-d) upon complexation with BF 2 . These novel boron-containing compounds display both planar and axial chiralities and were examined experimentally and computationally. In particular, their photophysical and chiroptical properties were studied and compared to newly prepared, simpler boranils (9a-d) exhibiting axial chirality only. Less sophisticated chiral architectures were shown to demonstrate overall stronger circularly polarized luminescence (CPL) activity., (© 2023 The Authors. Chirality published by Wiley Periodicals LLC.)

In the presented study, advanced experimental techniques, including electronic absorption and fluorescence spectroscopies [with Resonance Light Scattering (RLS)], measurements of fluorescence lifetimes in the frequency domain, calculations of dipole moment fluctuations, quantum yields, and radiative and non-radiative transfer constants, were used to characterize a selected analogue from the group of 1,3,4-thiadiazole, namely: 4-[5-(naphthalen-1-ylmethyl)-1,3,4-thiadiazol-2-yl]benzene-1,3-diol (NTBD), intrinsically capable to demonstrate enol → keto excited-states intramolecular proton transfer (ESIPT) effects. The results of spectroscopic analyses conducted in solvent media as well as selected mixtures were complemented by considering biological properties of the derivative in question, particularly in terms of its potential microbiological activity. The compound demonstrated a dual fluorescence effect in non-polar solvents, e.g. chloroform and DMSO/H 2 O mixtures, while in polar solvents only a single emission maximum was detected. In the studied systems, ESIPT effects were indeed observed, as was the associated phenomenon of dual fluorescence, and, as demonstrated for the DMSO: H 2 O mixtures, the same could be relatively easily induced by aggregation effects related to aggregation-induced emission (AIE). Subsequently conducted quantum-chemical (TD-)DFT calculations supported further possibility of ESIPT effects. The following article provides a comprehensive description of the spectroscopic and biological properties of the analyzed 1,3,4-thiadiazole derivatives, highlighting its potential applicability as a very good fluorescence probes as well as a compound capable of high microbiological activity., (© 2022. The Author(s).)

Enantiopure copper(I) chloride complexes bearing a monodentate N -(carbo[6]helicenyl)-NHC ligand have been prepared and characterized experimentally and computationally. Their high stability enables the stereochemistry to be probed by X-ray crystallography and NMR spectroscopy. The resolved enantiomeric complexes emit circularly polarized blue fluorescence with g lum ∼1.3 × 10 -3 in solution. The photophysical and chiroptical properties of these systems, with their helicene-centred origin, are similar to those of the organic helicene-benzimidazole precursor proligand, although the reverse axial chirality configuration is preferentially observed for the complex compared to the ligand.

Studies on molecular co-crystal type materials are important in the design and preparation of easy-to-absorb drugs, non-centrosymmetric, and chiral crystals for optical performance, liquid crystals, or plastic phases. From a fundamental point of view, such studies also provide useful information on various supramolecular synthons and molecular ordering, including metric parameters, molecular matching, energetical hierarchy, and combinatorial potential, appealing to the rational design of functional materials through structure-properties-application schemes. Co-crystal salts involving anionic d -metallate coordination complexes are moderately explored (compared to the generality of co-crystals), and in this context, we present a new series of isomorphous co-crystalline salts (PPh 4 ) 3 [M(CN) 6 ](H 3 PG) 2 ·2MeCN (M = Cr, 1 ; Fe, 2 ; Co 3 ; H 3 PG = phloroglucinol, 1,3,5-trihydroxobenzene). In this study, 1 - 3 were characterized experimentally using SC XRD, Hirshfeld analysis, ESI-MS spectrometry, vibrational IR and Raman, 57 Fe Mössbauer, electronic absorption UV-Vis-NIR, and photoluminescence spectroscopies, and theoretically with density functional theory calculations. The two-dimensional square grid-like hydrogen-bond {[M(CN) 6 ] 3- ;(H 3 PG) 2 } ∞ network features original {[M(CN) 6 ] 3- ;(H 3 PG) 4 } supramolecular cis -bis(chelate) motifs involving: (i) two double cyclic hydrogen bond synthons M(-CN⋅⋅⋅HO-) 2 Ar, {[M(CN) 6 ] 3- ; H 2 PGH}, between cis -oriented cyanido ligands of [M(CN) 6 ] 3- and resorcinol-like face of H 3 PG, and (ii) two single hydrogen bonds M-CN⋅⋅⋅HO-Ar, {[M(CN) 6 ] 3- ; H PGH 2 }, involving the remaining two cyanide ligands. The occurrence of the above tectonic motif is discussed with regard to the relevant data existing in the CCDC database, including the multisite H-bond binding of [M(CN) 6 ] 3- by organic species, mononuclear coordination complexes, and polynuclear complexes. The physicochemical and computational characterization discloses notable spectral modifications under the regime of an extended hydrogen bond network.

The calculation of magnetic transition dipole moments and rotatory strengths was implemented at the zeroth-order regular approximation (ZORA) two-component relativistic time-dependent density functional theory (TDDFT) level. The circular dichroism of the spin-forbidden ligand-field transitions of tris(ethylenediamine)cobalt(III) computed in this way agrees very well with available measurements. Phosphorescence dissymmetry factors g lum and the corresponding lifetimes are evaluated for three N-heterocyclic-carbene-based iridium complexes, two of which contain helicene moieties, and for two platinahelicenes. The agreement with experimental data is satisfactory. The calculations reproduce the signs and order of magnitude of g lum , and the large variations of phosphorescence lifetimes among the systems. The electron spin contribution to the magnetic transition dipole moment is shown to be important in all of the computations., (© 2022 The Authors. Published by Wiley-VCH GmbH.)

Chiral transition-metal complexes are of interest in many fields ranging from asymmetric catalysis and molecular materials science to optoelectronic applications or fundamental physics including parity violation effects. We present here a combined theoretical and experimental investigation of gas-phase valence-shell photoelectron circular dichroism (PECD) on the challenging open-shell ruthenium(III)-tris-(acetylacetonato) complex, Ru(acac) 3 . Enantiomerically pure Δ- or Λ-Ru(acac) 3 , characterized by electronic circular dichroism (ECD), were vaporized and adiabatically expanded to produce a supersonic beam and photoionized by circularly-polarized VUV light from the DESIRS beamline at Synchrotron SOLEIL. Photoelectron spectroscopy (PES) and PECD experiments were conducted using a double imaging electron/ion coincidence spectrometer, and compared to density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. The open-shell character of Ru(acac) 3 , which is not taken into account in our DFT approach, is expected to give rise to a wide multiplet structure, which is not resolved in our PES signals but whose presence might be inferred from the additional striking features observed in the PECD curves. Nevertheless, the DFT-based assignment of the electronic bands leads to the characterisation of the ionized orbitals. In line with other recent works, the results confirm that PECD persists independently on the localization and/or on the achiral or chiral nature of the initial orbital, but is rather a probe of the molecular potential as a whole. Overall, the measured PECD signals on Ru(acac) 3 , a system exhibiting D 3 propeller-type chirality, are of similar magnitude compared to those on asymmetric-carbon-based chiral organic molecules which constitute the vast majority of species investigated so far, thus suggesting that PECD is a universal mechanism, inherent to any type of chirality.

Mono- and di-boranil-substituted helicenes were prepared by BF 2 -borylation of the corresponding anils, readily synthesized by condensation of 2-amino- and 2,15-diamino-helicenes with 4-(diethylamino)salicylaldehyde. After enantiomeric resolution using HPLC, their chiroptical properties including circularly polarized fluorescence in solution and in PMMA films were investigated and rationalized with the help of NMR, X-ray and quantum-chemical calculations., (© 2021 Wiley-VCH GmbH.)

The square-planar [PtX 4 ] 2- complexes (X = Cl, Br) were successfully incorporated into preprogrammed hybrid organic-inorganic systems, exploiting their expected strong anion-π interactions with π-acidic hexaazaphenylenehexacarbonitrile, HAT(CN) 6 . The formation and properties of {[PtCl 4 ] 2- ; HAT(CN) 6 } aggregates in MeCN solution were evaluated based on their UV-Vis spectra to reveal the approximate binding constant K CT = 7.9(2) × 10 2 dm 3 mol -1 , molar absorption coefficient ε CT = 1.47(2) × 10 3 dm 3 mol -1 cm -1 , extent of electronic coupling H CT = 2.18 × 10 3 cm -1 , and electron delocalization α 2 = 1.75 × 10 -2 (α = 0.13). Strong [PtCl 4 ] 2- HAT(CN) 6 interactions in such adducts were also confirmed by the distinct shifts |Δδ iso | = 0.4 ppm of 13 C NMR peaks, when compared to the π-acid alone. The crystal structures of the resulting (PPh 4 ) 2 [PtX 4 ][HAT(CN) 6 ]·3MeCN (1-Cl - and 1-Br - ) solids are isomorphous with (PPh 4 ) 2 [Pt(CN) 4 ][HAT(CN) 6 ]·3MeCN (1-CN - ) reported by us previously. The halogenoplatinates occupy exactly the same nodes in the supramolecular network as cyanoplatinate, forming stacked {[PtX 4 ] 2- ;HAT(CN) 6 } ∞ columns that are stabilized by [PPh 4 ] + cations. However, contrary to the pale yellow coloration of the [Pt(CN) 4 ] 2- /HAT(CN) 6 systems, currently the dark violet or dark green coloration of solutions and crystalline phases were noted owing to the intense absorption in almost the whole visible region. DFT calculations reproduced the UV-Vis spectroscopic characteristics and linked it with the enhanced charge-transfer of the [PtX 4 ] 2- HAT(CN) 6 electronic interactions. Based on the isomorphism of all three (PPh 4 ) 2 [PtL 4 ][HAT(CN) 6 ]·3MeCN congeners we constructed and characterized the unprecedented, first ever anion-π-based binary rod-like core-shell crystalline composites 1-X@1-CN.

By attaching pyridine groups to a diaza[6]helicene, a helical, bis-ditopic, bis-N N-coordinating ligand can be accessed. Dinuclear rhenium complexes featuring this bridging ligand, of the form [{Re(CO) 3 Cl} 2 (N N-N N)], have been prepared and resolved to give enantiopure complexes. These complexes are phosphorescent in solution at room temperature under one- and two-photon excitation. Their experimental chiroptical properties (optical rotation, electronic circular dichroism and circularly polarized emission) have been measured. They show, for instance, emission dissymmetry factors of c.a. ±3x10 -3 . Quantum-chemical calculations indicate the importance of stereochemistry on the optical activity, pointing towards further design improvements in such types of complexes., (© 2020 Wiley-VCH GmbH.)

The first enantiopure chiral-at-rhenium complexes of the form fac-ReX(CO) 3 (:C^N) have been prepared, where :C^N is a helicene-N-heterocyclic carbene (NHC) ligand and X=Cl or I. These have complexes show strong changes in the emission characteristics, notably strongly enhanced phosphorescence lifetimes (reaching 0.7 ms) and increased circularly polarized emission (CPL) activity, as compared to their parent chiral models lacking the helicene unit. The halogen along with its position within the dissymmetric stereochemical environment strongly affect the photophysics of the complexes, particularly the phosphorescence quantum yield and lifetime. These results give fresh insight into fine tuning of photophysical and chiroptical properties of Re-NHC systems., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

2-Hydroxy aromatic Schiff bases that exhibit ESIPT (excited state intramolecular proton transfer) or TICT (twisted intramolecular charge transfer) photodeactivation pathways emerge as promising candidates for fluorescent sensors. In this computational work the influence of various substituents, differing in the electronic properties, on conformational preferences in the ground and S 1 excited state for a series of 2-hydroxy-1-naphthylmethylene-hydrazine-based ligands is systematically studied using (TD)DFT calculations. In order to shed light on physical factors which might determine the obtained conformational preferences, extensive bonding analyses are performed. The results highlight the crucial role of a substituent's ability to form not only well-established intramolecular hydrogen bonds (e.g., O-H···N) but also unintuitive nonclassic weak interactions (e.g., C-H···O, C-H···N, and C-H···H-C) in the modulation of the equilibrium between naphthol-imine and keto-amine forms, and planar or twisted conformations, and, thus, in determination of photophysical properties of the considered bases.

π-Helical push-pull dyes were prepared and their (chir)optical properties were investigated both experimentally and computationally. Specific fluorescent behaviour of bis-substituted system was observed with unprecedented solvent effect on the intensity of circularly polarized luminescence (CPL, dissymmetry factor decreasing from 10 -2 to 10 -3 with an increase in solvent polarity) that was linked to a change in symmetry of chiral excited state and suppression of interbranched exciton coupling. The results highlight the potential of CPL spectroscopy to study and provide a deeper understanding of electronic photophysical processes in chiral π-conjugated molecules., (This journal is © The Royal Society of Chemistry 2020.)

We describe a large-scale synthesis of a series of helicene-like compounds based on a dibenzo[ c ]acridine fragment by the Friedlander reaction. The series includes targeted constrained (closed) derivatives comprising 11 rings that exhibit very intense circularly polarized luminescence (CPL) ( g lum = 8 × 10 -3 ) contrary to their nonconstrained (open) 10-ring precursors that are not CPL active. The relationship between structure and chiroptical properties in the series is discussed with the aid of quantum-chemical calculations.

Fluorescent chemosensors with aggregation induced emission enhancement (AIEE) emerge as promising tools in the field of sensing materials. Herein, we report the design, synthesis and applicability of a Schiff base chemosensor 1-(benzo[1,3]dioxol-4-ylmethylene-hydrazonomethyl)-naphthalen-2-ol (Hbdhn) of AIE characteristics that exhibits highly effective and selective response towards Zn 2+ . The sensing effect of Hbdhn was evaluated by means of absorption/emission spectra and corresponding underlying photophysical mechanisms were proposed based on extensive quantum-chemical (TD)DFT calculations. The aggregated states in different DMSO/H 2 O ratios and in a presence of Zn 2+ were examined by fluorescence lifetime measurements, dynamic light scattering and scanning electron microscopy studies. The bioimaging abilities of Hbdhn were evaluated for Zn 2+ in HepG2 cancer cells. The results demonstrate instant, stable in time and reproducible, colorimetric turn-on response with superb selectivity and sensitivity of Hbdhn towards Zn 2+ , based on chelation enhanced fluorescence mechanism. AIEE improves further Hbdhn properties, leading to strong, long-lived fluorescence, with appearance of rod-like particles, in 90 % of water in DMSO and only 10 % of water in DMSO in the presence of Zn 2+ . All these features combined with successful biomaging studies make Hbdhn one of the most promising candidate for practical applications among recently proposed related systems., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A novel enantiopure bis-helicenic 2,2'-bipyridine system was prepared using a Negishi coupling. Thanks to the bipyridine unit, the coordination with Zn II and protonation processes were studied, revealing efficient tuning of photophysical (UV/visible and emission) and chiroptical properties (electronic circular dichroism and circularly polarized emission) of the system. The coordination/decoordination and protonation/deprotonation processes appeared reversible, thus constituting novel chiroptical switches.

Herein, the experimental physicochemical and chiroptical properties of a series of phosphahelicenes are reported, focusing on their UV/Vis absorption, luminescence, electronic circular dichroism, optical rotations, and circularly polarized luminescence. Furthermore, detailed analysis of absorption and ECD spectra performed with the help of quantum-chemical calculations allowed us to highlight general features of these helicenic phosphines. Finally, due to well-suited electrochemical properties and thermal stability, the systems were successfully used as emitters in organic light-emitting diodes., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The synthesis, crystal structures, spectroscopic characterization, and comprehensive quantum-chemical calculations for a novel series of anion-π hybrid salts (XPh 4 ) 2 [M(CN) 4 ][HAT(CN) 6 ]⋅3 MeCN (X=P, M=Ni II (1), Pd II (3), Pt II (5); X=As, M=Ni II (2), Pd II (4), Pt II (6); HAT(CN) 6 =1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile) are presented. The systems comprise 1D {[M(CN) 4 ] 2- ;[HAT(CN) 6 ]} ∞ stacks, in which the electron-rich metal complexes adjust their orientation to match the electron-deficient areas of HAT(CN) 6 . Electronic charge-transfer interactions along the stacks result in polarization of electron density within HAT(CN) 6 and in perturbations along the {[M(CN) 4 ] 2- ;[HAT(CN) 6 ]} ∞ contacts. Electronic structure analysis suggests, for example, a relocation of 0.1-0.2 e per molecule from [M(CN) 4 ] 2- to HAT(CN) 6 and anion-π interaction energies of around -65 kcal mol -1 . A reversible structural single-crystal-to-single-crystal transformation, through desolvation/resolvation processes in the solid state, is also reported and a scheme for the formation of anion-π [M(CN) 4 ] 2- /HAT(CN) 6 adducts in MeCN is proposed., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Introducing one or two alkynyl-iron moieties onto a carbo[6]helicene results in organometallic helicenes (2 a,b) that display strong chiroptical activity combined with efficient redox-triggered switching. The neutral and oxidized forms have been studied in detail by electronic and vibrational circular dichroism, as well as by Raman optical activity (ROA) spectroscopy. The experimental results were analyzed and spectra were assigned with the help of first-principles calculations. In particular, a recently developed method for ROA calculations under resonance conditions has been used to study the intricate resonance effects on the ROA spectrum of mono-iron ethynylhelicene 2 a., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Enantiopure P- and M-carbo[6]helicenes substituted with one or two tetracyanobutadiene moieties at positions 2 and 15 have been prepared. Grafting of these electron-accepting groups onto the π-helical core resulted in strong charge-transfer effects, which greatly affected the UV/Vis, electronic circular dichroism (ECD), and two-photon absorption (TPA) responses. The ECD signal was found to be reversibly switched by applying a redox stimulus., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Model catalysts for CO 2 /epoxide copolymerization based on Co(III) complexes were studied, with focus on the preference of their alternative isomers, cisβ vs. trans. The systems range from model structures without the co-catalyst, as derived from crystallographic data, to complex models with two (CH 2 ) 4 N + R 3 co-catalyst chains (R = Me, Bu) grafted onto a Co(III)-salcy core. To explore the conformational space of the latter complexes, a computational protocol was developed, combining a systematic model-building approach with static and molecular dynamics calculations, and multilevel energy assessment (PM7 and DFT). Results demonstrate an influence of the co-catalyst on the relative stability of the isomers. The cisβ isomer is preferred for complexes without N + -chains and the cisβ ↔ trans isomerization is feasible. Five-coordinate species and open-shell electronic configurations are energetically disfavored. The cisβ preference decreases with the introduction and enlargement of (CH 2 ) 4 N + R 3 : both isomers can be populated for R = Me, while the trans isomer is visibly preferred for R = Bu. © 2018 Wiley Periodicals, Inc., (© 2018 Wiley Periodicals, Inc.)

Palladium(II) acetate (1) and two new complexes of the ligand α,α,α',α'-tetramethyl-1,3-benzenedipropionate (esp 2- ), C s -Pd 3 (esp) 3 ( C s -2) and C 3 h -Pd 3 (esp) 3 ( C 3 h -2), are studied in the solid state and in solution. Variable-temperature NMR and DFT studies of C s -2 reveal an unusual shielding region above the Pd atoms. The compounds show a surprising quasi-reversible reduction between -880 and -1200 mV versus Fc/Fc + , and the Pd 3 (esp) 3 complexes may be cleanly reduced electrochemically. EPR spectra of reduced samples show pseudo-axial signals with 105 Pd hyperfine coupling, consistent with unprecedented, isostructural Pd 3 5+ species with a valence-trapped Pd II -Pd II -Pd I electronic structure.

A pentanuclear Cu II 5 -hydroxo cluster possessing an unusual linear-shaped configuration was formed and crystallized under hydrothermal conditions as a result of the unique cooperation of bridging 1,2,4-triazole ligand ( trans-1,4-cyclohexanediyl-4,4'-bi(1,2,4-triazole) ( tr 2 cy)), Mo VI -oxide, and CuSO 4 . This structural motif can be rationalized by assuming in situ generation of {Cu 2 Mo 6 O 22 } 4- anions, which represent heteroleptic derivatives of γ-type [Mo 8 O 26 ] 4- further interlinked by [Cu 3 (OH) 2 ] 4+ cations through [ N- N] bridges. The framework structure of the resulting compound [Cu 5 (OH) 2 ( tr 2 cy) 2 Mo 6 O 22 ]·6H 2 O (1) is thus built up from neutral heterometallic {Cu 5 (OH) 2 Mo 6 O 22 } n layers pillared with tetradentate tr 2 cy. Quantum-chemical calculations demonstrate that the exclusive site of the parent γ-[Mo 8 O 26 ] 4- cluster into which Cu II inserts corresponds with the site that has the lowest defect ("MoO 2 vacancy") formation energy, demonstrating how the local metal-polyoxomolybdate chemistry can express itself in the final crystal structure. Magnetic susceptibility measurements of 1 show strong antiferromagnetic coupling within the Cu 5 chain with exchange parameters J 1 = -500(40) K (-348(28) cm -1 ), J 2 = -350(10) K (-243(7) cm -1 ) and g = 2.32(2), χ 2 = 6.5 × 10 -4 . Periodic quantum-chemical calculations reproduce the antiferromagnetic character of 1 and connect it with an effective ligand-mediated spin coupling mechanism that comes about from the favorable structural arrangement between the Cu centers and the OH - , O 2- , and tr 2 cy bridging ligands.

The charged, electroactive bipyridine-helicene-ruthenium(III) complex [4] .+ ,PF 6 - has been prepared from 3-(2-pyridyl)-4-aza[6]helicene and a Ru-bis-(β-diketonato)-bis-acetonitrile precursor (β-diketonato: 2,2,6,6-tetramethyl-3,5-heptanedionato). Its chiroptical properties (electronic circular dichroism and optical rotation) were studied both experimentally and theoretically and suggest the presence of 2 diastereoisomers, namely (P,Δ)- and (P,Λ)-[4] .+ ,PF 6 - ) and their mirror-images (M,Λ)- and (M,Δ)-[4] .+ ,PF 6 ((M,Δ*)-[4] - ) and their mirror-images (M,Λ)- and (M,Δ)-[4] .+ ,PF 6 - ((M,Δ*)-[4] .+ ,PF 6 - ). The electrochemical reduction of (P,Δ*)-[4] .+ ,PF 6 - to neutral complex (P,Δ*)-4 was performed and revealed strong changes in the UV-vis and electronic circular dichroism spectra. A reversible redox-triggered chiroptical switching process was then achieved., (© 2018 Wiley Periodicals, Inc.)

Molecular and macromolecular chiral π-conjugated diketopyrrolopyrrole (DPP)-helicene derivatives were prepared and their chiroptical properties examined experimentally and theoretically. Exciton coupling leads to red and near-infrared circularly polarized absorption and luminescence arising from the achiral DPP units in the helical environment, highlighting an interesting synergy between the chiral helicene and the organic dye.

Chiral metal-organic frameworks have attracted interest for enantioselective separations and catalysis because of their high crystallinity and pores with tunable shapes, sizes, and chemical environments. Chiral frameworks of the type M 2 (dobpdc) (M = Mg, Mn, Fe, Co, Ni, Zn; dobpdc 4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) seem particularly promising for potential applications because of their excellent stability, high internal surface areas, and strongly polarizing open metal coordination sites within the channels, but to date these materials have been isolated only in racemic form. Here, we demonstrate that when appended with the chiral diamine trans-1,2-diaminocyclohexane (dach), Mg 2 (dobpdc) adsorbs carbon dioxide cooperatively to form ammonium carbamate chains, and the thermodynamics of CO 2 capture are strongly influenced by enantioselective interactions within the chiral pores of the framework. We further show that it is possible to access both enantiomers of Mg 2 (dobpdc) with high enantiopurity (≥90%) via framework synthesis in the presence of varying quantities of d-panthenol, an inexpensive chiral induction agent. Investigation of dach-M 2 (dobpdc) samples following CO 2 adsorption-using single-crystal and powder X-ray diffraction, solid-state nuclear magnetic resonance spectroscopy, and density functional theory calculations-revealed that the ammonium carbamate chains interact extensively with each other and with the chiral M 2 (dobpdc) pore walls. Subtle differences in the non-covalent interactions accessible in each diastereomeric phase dramatically impact the thermodynamics of CO 2 adsorption.

A fused π-helical N-heterocyclic carbene (NHC) system was prepared and examined through its diastereoisomerically pure cycloiridiated complexes. The latter display light-green phosphorescence with unusually long lifetimes and circular polarization that depends on both the helical NHC P/M stereochemistry and the iridium Δ/Λ stereochemistry. These unprecedented features are attributed to extended π conjugation within the helical carbenic ligand and efficient helicene-NHC-Ir interaction., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Computations of natural optical activity (OA) from first principles (ab initio) have become indispensable in chiroptical studies of molecular systems. Calculations are used to assign absolute configurations and to analyze chiroptical data, providing a basis for understanding their origin as well as for assigning and predicting experimental results. In this article, methodology for OA computations is outlined and accompanied by a review of selected, mainly recent (ca. 2010-2016) achievements in optical rotation, electronic and vibrational circular dichroism, and Raman OA calculations. We discuss some important aspects of the computational models and methodological developments, along with recently proposed approaches to analyze and interpret OA parameters. We highlight applications of chiroptical computational methods in studies of helicenes and chiral nanoparticles.

Five tris(β-diketonato) complexes of ruthenium(III), chromium(III), and cobalt(III) [Ru(Buacac) 3 (1), Ru(Oacac) 3 (2), Cr(Buacac) 3 (3), Cr(Oacac) 3 (4), and Co(Buacac) 3 (5), where Buacac = 3-butylpentane-2,4-dionato and Oacac = 3-octylpentane-2,4-dionato] with a chiral propeller-like structure have been prepared. Ligands and complexes syntheses are presented together with characterization of the compounds by 1 H and 13 C NMR spectroscopy, mass spectrometry, IR, UV-vis, electronic circular dichroism (ECD) spectroscopy, electrochemistry studies, and first-principles calculations. The crystal structures of 1 and 5 have also been obtained and analyzed. A comparison of the 1 H NMR spectra of diamagnetic (ligands and 5) and paramagnetic (1 and 2) species is presented. Optical resolution of the five complexes has been achieved for the first time by supercritical fluid chromatography using a chiral column, giving rise to very high purity grades in all cases. ECD measurements and calculations have led to the assignment of the absolute configuration, Δ or Λ, of each enantiomer for 1-5. Spectroelectrochemical UV-vis and ECD studies have been performed on ruthenium Λ-2 and chromium Λ-4 complexes, revealing their redox-triggered chiroptical switching confirming the noninnocence character of the β-diketonate ligands.

Hexacyanidometalates (M = Fe III , Co III ) and multisite anion receptor HAT(CN) 6 (1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile) recognize each other in acetonitrile solution and self-assemble into the novel molecular networks (PPh 4 ) 3 [M(CN) 6 ][HAT(CN) 6 ] (M = Fe, 1; Co, 2) and (AsPh 4 ) 3 [M(CN) 6 ][HAT(CN) 6 ]·2MeCN·H 2 O (M = Fe, 3; Co, 4). 1-4 contain the stacked columns {[M(CN) 6 ] 3- ;[HAT(CN) 6 ]} ∞ separated by the organic cations. All of the M-C[triple bond, length as m-dash]N vectors point collectively towards the centroids of pyrazine rings on neighboring HAT(CN) 6 molecules, with N cyanide centroid pyrazine distances that are under 3 Å. The directional character and structural parameters of the new supramolecular synthons correspond to collective triple anion-π interactions between the CN - ligands of the metal complexes and the π-deficient areas of HAT(CN) 6 . Physicochemical characterisation (IR spectroscopy, UV-Vis spectroscopy, cyclic voltammetry) and dispersion-corrected DFT studies reveal the dominating charge-transfer (CT) and polarisation characters of the interactions. The electronic density flow occurs from the CN - ligands of [M(CN) 6 ] 3- to the HAT(CN) 6 orbital systems and further, toward the peripheral -CN groups of HAT(CN) 6 . Solid-state DFT calculations determined the total interaction energy of HAT(CN) 6 to be ca. -125 kcal mol -1 , which gives ca. -15 kcal mol -1 per one CN - HAT(CN) 6 contact after subtraction of the interaction with organic cations. The UV-Vis electronic absorption measurements prove that the intermolecular interactions persist in solution and suggest a 1 : 1 composition of the anion-π {[M(CN) 6 ] 3- ;[HAT(CN) 6 ]} chromophore, with the formation constant K add = (5.8 ± 6) × 10 2 dm 3 mol -1 and the molar absorption coefficient ε add = 180 ± 9 cm -1 dm 3 mol -1 at 600 nm, as estimated from concentration-dependent studies.

Four members of a new class of cycloborylated hexa-, octa-, and deca-helicenes (1 a-d) have been prepared in enantiopure form, along with two cycloplatinated deca-helicenes (1 d', 1 d 1 ), further extending the family of cycloplatinated hexa- and octa-helicenes reported previously. The azabora[n]helicenes display intense electronic circular dichroism and large optical rotations; the dependence of the optical activity on the size of the helix (n=6, 8, 10) and the number of boron atoms (1 or 2) has been examined in detail both experimentally and theoretically. The photophysical properties (nonpolarized and circularly polarized luminescence) of these new fluorescent organic helicenes have been measured and compared with the corresponding organometallic phosphorescent cycloplatinated derivatives (1 a 1 -d 1 )., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The first helicene-NHC-iridium complexes have been prepared in enantiopure forms. Their stereochemical, electronic, and chiroptical features were characterized experimentally and via first-principles calculations, highlighting the helical and iridium-centered chirality.

The combination of a bis-alkynyl-helicene moiety with two iron centers leads to novel electroactive species displaying unprecedented redox-triggered chiroptical switching. Upon oxidation, strong changes of vibrational modes (either local or extended coupled modes) are detected by vibrational circular dichroism and Raman optical activity. Remarkably, the sign of the optical rotation at 1.54 µm (that is, at wavelengths typically used for telecommunications) changes upon oxidation while the topology and stereochemistry of the helicene remain unchanged., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The molecular conformation of a bis-helicenic terpyridine system is strongly modified upon binding to Zn(ii) ion, a process that is accompanied by large changes in the optical and chiroptical properties. This system affords a new type of helicene-based chiroptical switching.

Monometallic gold(I)-alkynyl-helicene complexes (1 a,b) and bimetallic gold(I)-alkynyl-helicene architectures featuring the presence (2 a,b) or absence (3 a,b) of aurophilic intramolecular interactions were prepared by using different types of phosphole ligands (mono-phosphole L1 or bis-phospholes L2,3). The influence of the Au(I) d(10) metal center(s) on the electronic, photophysical, and chiroptical properties of these unprecedented phosphole-gold(I)-alkynyl-helicene complexes was examined. Experimental and theoretical results highlight the importance of ligand-to-ligand-type charge transfers and the strong effect of the presence or absence of Au(I) -Au(I) interactions in 2 a,b., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Helicenes are fascinating molecules owing to their unusual properties and applications in many fields from catalysis to organic electronics. Herein, we report a straightforward pathway for the synthesis of helicene-like molecules on a gram scale in an enantiopure form. Thin-film materials with good propagating optical properties and very high chiroptical responses have been grown by using pulsed laser ablation without altering the structure or the enantiopurity of the molecules. Moreover, electronic and vibrational circular dichroism spectroscopies coupled with theoretical calculations enabled some dependences of the chiroptical properties with the structure to be highlighted, for example, effects of rigidification, aromatization, or the state of matter (liquid versus solid)., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)