Zethrene and Dibenzozethrene: Masked Biradical Molecules?

The syntheses, structures, and physical properties of dibenzozethrenes were explored. The results thus obtained were compared with those for zethrenes. Dibenzozethrenes were synthesized by the nickel‐catalyzed cyclodimerization of 9‐ethynyl‐1‐iodoanthracenes. The substituents in zethrene and dibenzozethrene twisted their backbones, and remarkably influenced their properties. Unlike closed‐shell disubstituted derivatives, the parent zethrene and dibenzozethrene are singlet open‐shell biradicals, which were studied by variable‐temperature ¹H NMR, ESR, SQUID and computational methods. Since substituents were observed to affect significantly the biradical properties, the relevant mechanisms were analyzed. The nonlinear optical performance of each of these compounds depends on its π‐conjugation and biradical properties. Dibenzozethrenes have larger two‐photon absorption cross‐sections than zethrenes, as most strongly evidenced by the parent dibenzothrene [σ_max=4323 GM at 530 nm].     

Zethrene and Dibenzozethrene: Masked Biradical Molecules?

The syntheses, structures, and physical properties of dibenzozethrenes were explored. The results thus obtained were compared with those for zethrenes. Dibenzozethrenes were synthesized by the nickel‐catalyzed cyclodimerization of 9‐ethynyl‐1‐iodoanthracenes. The substituents in zethrene and dibenzozethrene twisted their backbones, and remarkably influenced their properties. Unlike closed‐shell disubstituted derivatives, the parent zethrene and dibenzozethrene are singlet open‐shell biradicals, which were studied by variable‐temperature ¹H NMR, ESR, SQUID and computational methods. Since substituents were observed to affect significantly the biradical properties, the relevant mechanisms were analyzed. The nonlinear optical performance of each of these compounds depends on its π‐conjugation and biradical properties. Dibenzozethrenes have larger two‐photon absorption cross‐sections than zethrenes, as most strongly evidenced by the parent dibenzothrene [σ_max=4323 GM at 530 nm].     

On Chiral Space Groups and Chiral Molecules

Aschemicalnomenclaturewasoriginallydevelopedforcompoundsinthesolutionstate,thereissomeconfusionintheproperuseoftheterm慶hiralfordescribingcertaincrystalstructures.Thishasledtoanumberofcompoundsbeingincorrectlycategorizedasbeingchiralalthoughtheybelongtocentrosymmetricspacegroupsorthosehavingmirrorplanes.Achiralcompoundthatseparatesfromsolutionasacrystallinematerialmustnecessarilypackinamotifsuchthatothermoleculesintheunitcellarenotsuperimposableontheirownmirrorimages.Theconditionforopticalacti…     

Why are Cold Molecules so Hot?

Brrrr! Cold molecule and cold atom research are juxtaposed and the challenges in cooling and trapping molecules are recounted. Both indirect and direct techniques of producing cold and slow molecules (such as buffer‐gas cooling and magnetic trapping, see picture) are described. Advanced techniques of manipulating cold or slow molecules are reviewed and ongoing work with cold molecules is outlined.

     

Heterocyclic π-Donors,Macrocycles and Cage Molecules

Abstract

π-Donors based on TIT-units have been intensively studied due to their potential use in conducting molecular materials. It therefore appeared of interest to use the readily avaible dithiolate (1) for the syntheses of macrocycles, exemplified by (3) and (4) and the lTF-cage molecules (5) - (7) obtained by intramolecular coupling^[1]:     

New Host Molecules with Imidazoliums as Functional Arms:Syntheses and Anion Recognition

The bridged tri-imidazoliums 3.3X^--5.3X^-(X^-=PF6^-,Br^-,I^-)and bis-imidazoliums 6.2PF6^- were synthesized by N-quaternization of imidazole derivative 1 in acetonitrile under reflux.UV spectroscopic titration experiments showed that the halide salts and hexafluorophosphate salts of these imidazoliums exhibited good recognition toward anions in water and in acetonitrile,respectively.     

Ab initio Description of Nuclear Motion in Nonrigid M k XY n (k≥1) Molecules with Quasirigid XY n Fragments

For nonrigid M _k XY _n (k1) molecules, a model is constructed that describes the motion of k M nuclei relative to the quasirigid XY _n fragment taking into account 3^* k degrees of freedom. The parameters of the potential and kinetic terms of the model Hamiltonian are determined from results of ab initio calculations of the properties of a molecule and its fragments. Solutions of the corresponding Schrödinger equations are obtained by a variational method using bases constructed from products of spherical harmonics and harmonic–oscillator eigenfunctions. The form of model Hamiltonians for nonrigid MXY₄ and M₂XY₄ molecules with quasitetrahedral XY₄ fragments are discussed in detail. Group–theoretical analysis of the symmetry of the Hamiltonians is performed. It is shown that the molecular symmetry groups of nonrigid MXY₄ and M₂XY₄ molecules are the G ₂₄ and G ₄₈ groups, which are isomorphic to the T _d and O _h point groups, respectively.     

Carpet Beater Molecules: Synthesis and Characterization of Functional Hexa-peri-benzocoronene–Alkyne Coupling Products

Within the scope of this paper, nine π-expanded mono-substituted 5,8,11,14,17-pentakis-(tert-butyl)-hexa-peri-hexabenzocoronenes (HBC) are introduced. 2-Iodo-5,8,11,14,17-pentakis-(tert-butyl)-hexa-peri-hexabenzocoronene served as precursor and was reacted with ethynyltrimethylsilane in a Sonogashira coupling reaction. The acetylene unit is used as a linker and can undergo another Sonogashira coupling reaction combining different phenyl coupling partners with the HBC core. The electron-withdrawing groups such as nitrile, pyridine and carbonyl species (aldehyde, methylester, carboxylic acid) as well as the three quinoxaline based species (diphenylquinoxaline, dibenzo[a,c]phenazine, phenanthro[4’,5’-a,b,c]phenazine) serve as substitution moieties. Their influence on the optoelectronic properties were investigated by UV/Vis absorption spectroscopy demonstrating a maximum redshift of 7 nm compared to starting compound 2-Iodo-5,8,11,14,17-pentakis-(tert-butyl) HBC. As for the phenanthro[4’,5’-a,b,c]phenazine substituted HBC a dramatic decrease in the intensity of the absorption of the UV/Vis spectrum was observed. The fluorescence spectroscopy pointed out that the dibenzo[a,c]phenazine and phenanthro[4’,5’-a,b,c]phenazine substitution changed the spectra to one broad peak departing from the characteristic HBC-like emission pattern.     

From Disymmetric Molecules to Chiral Polymers: A New Twist for Supramolecular Synthesis?

A new branch of crystal engineering appears to have borne fruit: A noncovalently bonded network consisting of the complex illustrated as a stick model on the right is converted directly into a coordination polymer with a similar molecular architecture. The implications of the new work extend beyond the boundaries of coordination chemistry since the same strategy should work equally well in organic and organometallic systems.     

Еxcitation Energy Relaxation Processes Involving Chlorophyll Molecules In Vitro: Solutions and Self-Organized Nanoassemblies

Russian Journal of General Chemistry - The review presents the main results obtained by the Belorussian scientific school of Acad. G.P. Gurinovich and his followers in the in the research on the...     

Benzotriazole-Based 3D Four-Arm Small Molecules Enable 19.1 % Efficiency for PM6 : Y6-Based Ternary Organic Solar Cells

A third component featuring a planar backbone structure similar to the binary host molecule has been the preferred ingredient for improving the photovoltaic performance of ternary organic solar cells (OSCs). In this work, we explored a new avenue that introduces 3D-structured molecules as guest acceptors. Spirobifluorene (SF) is chosen as the core to combine with three different terminal-modified (rhodanine, thiazolidinedione, and dicyano-substituted rhodanine) benzotriazole (BTA) units, affording three four-arm molecules, SF-BTA1, SF-BTA2, and SF-BTA3, respectively. After adding these three materials to the classical system PM6 : Y6, the resulting ternary devices obtained ultra-high power-conversion efficiencies (PCEs) of 19.1 %, 18.7 %, and 18.8 %, respectively, compared with the binary OSCs (PCE=17.4 %). SF-BTA1-3 can work as energy donors to increase charge generation via energy transfer. In addition, the charge transfer between PM6 and SF-BTA1-3 also acts to enhance charge generation. Introducing SF-BTA1-3 could form acceptor alloys to modify the molecular energy level and inhibit the self-aggregation of Y6, thereby reducing energy loss and balancing charge transport. Our success in 3D multi-arm materials as the third component shows good universality and brings a new perspective. The further functional development of multi-arm materials could make OSCs more stable and efficient.     

Interaction between Metal in Metallo Enzyme and Small Biological Molecules

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Zirconocene Catalysts: Ion‐pairs,Zwitterions, or Weakly Bound Molecules?

The bonding between electron deficient zirconocene complexes such as [(η⁵‐C₅Me₅)₂ZrR]⁺ and the counterions [(C₆F₅)₃BR]^– (R = CH₃, 1 , R = H, 2 ) has been investigated by DFT and extended Hückel calculations. The molecular bonding analysis has been carried out in the light of the structural information on the inter‐ion interactions available for these and other similar electron deficient coordinatively unsaturated zirconocene complexes. It has been shown that the “anion‐cation” interactions in 1 and 2 are different manifestations of the same need to provide electron density to the metal centre. In 1 this is achieved via the ‐C–H σ‐bonds and has been described as a pseudo‐agostic interaction, whereas in 2 electron donation occurs via the phenyl F‐atoms. The study of the covalent component of the bonding between the ionic components has shown that the weak electron donation, though not sufficient to saturate the metal centre, stabilises the unsaturated species and allows it to have a longer life time. It has been inferred that in the homogenous Ziegler‐Natta catalytic process the approach of a strongly coordinating molecule, such as an olefin in the polymerisation, destroys the weak interaction and allows the reaction to proceed whilst the ion‐pairing maintains the counterion in proximity of the complex.     

ChemInform Abstract: Where Do the Forces in Molecules Come from? A Density Functional Study of N2 and HCl.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Do Anionic π Molecules Aggregate in Solution? A Case Study with Multi-interactive Ligands and Network Formation

An anionic π molecule can form an aggregate when a multi-interactivity is introduced, in sharp contrast to common anionic molecules that are generally difficult to stack on each other. We found that a multi-interactive ligand, 2,5,8-tri(4′-pyridyl)-1,3,4,6,7,9-hexaazaphenalenate (TPHAP⁻) exhibited a large Stokes shift and an intramolecular charge transfer, both of which were sensitive to hydrogen-bonding media. An anionic potassium salt of TPHAP⁻ in methanol formed various aggregation states depending on the concentration examined; this was revealed by steady-state spectroscopic and fluorescence lifetime measurements. Self-assembling cadmium ions and the ligands can create several morphological crystals that are controlled by the ligand concentration, among which three new structures were determined by single-crystal analysis. The X-ray structures obtained suggest that the aggregation states of the ligand in solution can be transferred to the solid system of the porous coordination networks.     

Broadband Vibrational Cooling of Cold Cesium Molecules： Theory and Experiments

The use of a broadband, frequency shaped femtosecond laser on translationally cold cesium molecules has recently demonstrated to be a very efficient method of cooling also the vibrational degree of freedom. A sample of cold molecules, initially distributed over several vibrational levels, has thus been transfered into a single selected vibrational level of the singlet X^1∑g ground electronic state. Our method is based on repeated optical pumping by laser light with a spectrum broad enough to excite all populated vibrational levels but limited in its frequency bandwidth with a spatial light modulator. In such a way we are able to eliminate transitions from the selected level, in which molecules accumulate. In this paper we briefly report the main experimental results and then address, in a detailed way by computer simulations, the perspectives for a ＂complete＂ cooling of the molecules, including also the rotational degree of freedom. Since the pumping process strongly depends on the relative shape of the ground and excited potential curves, ro-vibrational cooling through different excited states is theoretically compared.     

Can Li Atoms Anchored on Boron- and Nitrogen-Doped Graphene Catalyze Dinitrogen Molecules to Ammonia? A DFT Study

The most successful electrochemical conversion of ammonia from dinitrogen molecule reported to date is through a Li mediated mechanism. In the framework of the above fact and that Li anchored graphene is an experimentally feasible system, the present work is a computational experiment to identify the potential of Li anchored graphene as a catalyst for N₂ to NH₃ conversion as a function of (a) minimum number of Li atoms needed for anchoring on graphene sheets and (b) the role of chemical modification of graphene surfaces. The studies bring forth an understanding that Li anchored graphene sheets are potential catalysts for ammonia conversion with preferential adsorption of N₂ through end-on configuration on Li atoms anchored on doped and pristine graphene surfaces. This mode of adsorption being characteristic of Nitrogen Reduction Reaction (NRR) through enzymatic pathway, examination of the same followed by analysis of electronic properties demonstrates that tri-Li atoms (Tri Atom Catalysts, TACs) are more efficient as catalysts for NRR as compared to two Li atoms (Di Atom Catalysts, DACs). Either way, the rate determining step was found to be *NH₂→*NH₃ step (mixed pathway) with ΔG_max=1.02 eV and *NH₂−*NH₃→*NH₂ step (enzymatic pathway) with ΔG_max=1.11 eV for 1B doped TAC and DAC on graphene sheet, respectively. Consequently, this work identifies the viability of Li anchored graphene based 2-D sheets as hetero-atom catalyst for NRR.