Hydride Transfer to Gold: Yes or No? Exploring the Unexpected Versatility of Au···H‐M Bonding in Heterobimetallic Dihydrides

The potential for coordination and H-transfer from Cp2MH2 (M = Zr, W) to gold(I) and gold(III) complexes was explored in a combined experimental and computational study. [(L)Au]+ cations react with Cp2WH2 giving [(L)Au(κ2-H2WCp2)]+ (L = IPr ( 1 ), cyclic (alkyl)(amino)carbene ( 2) , or phosphines PPh3 (3) and Dalphos-Me (4) [IPr = 1,3-bis(diisopropylphenyl)imidazolylidene; Dalphos-Me = di(1-adamantyl)-2-(dimethylamino)phenyl-phosphine], while [Au(DMAP)2]+ (DMAP = p-dimethylaminopyridine) affords the C2-symmetric [Au(κ-H2WCp2)2]+ (5) . The Dalphos complex 4 can be protonated to give the bicationic adduct 4H , showing Au(I)…H+-N hydrogen bonding. The gold(III) Lewis acid [(C^N-CH)Au(C6F5)(OEt2)]+ binds Cp2WH2 to give an Au-H-W σ-complex. By contrast, the pincer species [(C^N^C)Au]+ adds Cp2WH2 by a purely dative W→Au bond, without Au···H interaction. The biphenyl-based chelate [(C^C)Au]+ forms [(C^C)Au(µH)2WCp2]+, with two 2-electron-3-centre W-H…Au interactions and practically no Au-W donor acceptor contribution. In all these complexes strong but polarised W-H bonds are maintained, without H-transfer to gold. On the other hand, the reactions of Cp2ZrH2 with gold complexes led in all cases to rapid H-transfer and formation of gold hydrides. Relativistic DFT calculations were used to rationalize the striking reactivity and bonding differences in these heterobimetallic hydride complexes along with an analysis of their characteristic NMR parameters and UV-Vis absorption properties

2-arylthienyl-substituted 1,3-benzothiazoles as new nonlinear optical chromophores

A series of nonlinear optical chromophores 6 containing a substituted benzothiazole ring have been synthesized and characterized. 1,3-Benzothiazoles 6 were prepared by reacting various formyl derivatives of thienyl compounds with ortho-aminobenzenethiol in fair to excellent yields. These in turn were prepared by Suzuki coupling between aryl and thienyl precursors. The electronic interactions between donor and acceptor end groups in the conjugated 1,3-benzothiazoles 6 are expressed in the intense and markedly solvatochromic CT transitions. The solvatochromic behaviour of compounds 6 was determinated by linear regression analyses of absorption maxima in several solvents, whereby benzothiazole 6f was found to be a very appropriate indicator dye whose absorption wavenumbers (νmax= 1590 cm –1) in aliphatic and dipolar aprotic and in aromatic and chlorinated solvents excellently correlate with the π* values defined by Kamlet and Taft. Hyper-Rayleigh scattering was used to measure the first hyperpolarizabilities β of the mentioned compounds. Thermo gravimetric analysis (TGA) was used to evaluate their thermal stability. The experimental results indicate that good nonlinearity–thermal stability is well balanced for chromophores 6, making them good candidates for device applications.Fundação para a Ciência e Tecnologi

Ferroelectric nanofibers with an embedded optically nonlinear benzothiazole derivative

We report measurements of the molecular first hyperpolarizability, thermal stability, photophysical, piezoelectric and ferroelectric properties of a benzothiazole derivative bearing an arylthiophene π-conjugated bridge both in solution and when embedded into a poly (L-lactic acid) (PLLA) matrix in the form of electrospun fibers with an average diameter of roughly 500 nm. The embedded nanocrystalline phenylthienyl-benzothiazole derivative, with crystal sizes of about 1.4 nm resulted in a good piezoelectric response from these functionalized electrospun fibers, indicative of a polar crystalline structure.Fundação para a Ciência e a Tecnologia (FCT

Organic Sensitizer

The photophysics and solar cell efficiency of organic sensitizers comprising a cyanoacrylic acid group are greatly influenced by an equilibrium between the neutral ("non-deprotonated", COOH) and anionic ("deprotonated", COO ) forms, whose ratio depends on the solvent polarity and its H-bonding properties, dye concentration, and temperature used. Herein, we report a detailed investigation on the relationship between the portions of COOH and COO- dye forms and the photophysical and solar cell properties of an organic dipolar sensitizer, BTZA-II, bearing triphenylamine electron-donating and benzothiazole electron-withdrawing moieties. The photophysics has been studied by stationary and timeresolved fluorescence spectroscopy in apolar and polar solvents with a dye concentration ranging from 5 x 10(-7) to 5 x 10(-5) M, also upon addition of small amounts of an external acid or base to change the solvent acidity, allowing us to distinguish the contribution and lifetime of the neutral and anionic forms. The fluorescence of BTZA-II in apolar toluene originates from the neutral form, which has a lifetime of 1.9 ns. Addition of a strong base (1,8-diazabicyclo[5.4.0]undec-7-ene, DBU) shifts the equilibrium toward the less fluorescent anionic COO- form with a lifetime of 1.1 ns. The situation is different in the polar acetonitrile, where the fluorescence of the anionic form dominates (with a lifetime of 2.0 ns). Adding small amounts of acetic acid (AcOH) protonates the COO- form of the BTZA-II dye and reveals significant quenching of the fluorescence because of the increased contribution of the neutral species with a lifetime of 0.4-0.5 ns. This quenching of the neutral species in acetonitrile has been also observed in concentrated solutions and is due to excited-state proton transfer. By contrast, the photophysics of a dye Btz-NPh2, similar to BTZA-II but without the cyanoacrylic acid group, is not affected upon adding acetic acid (H-donor) or DBU base (H-acceptor), which rules out the Bronsted-base role of the benzothiazole scaffold in the aforementioned observations. Finally, dyesensitized solar cells (DSSCs) with a solid-state electrolyte were prepared from toluene and toluene + acid solutions. A significant increase in the solar cell efficiency, eta, by 58% (eta reaching a value of 4.9%) has been achieved after addition of a small, appropriate amount of acetic acid into the initial BTZA-II dye solution

Quadrupolar benzobisthiazole-cored arylamines as highly efficient two-photon absorbing fluorophores

A computer-aided design of novel D-?-A-?-D styrylamines containing five isomeric benzobisthiazole moieties as the electron-accepting core has revealed the linear centrosymmetric benzo[1,2-d:4,5-d?]bisthiazole as the most promising building block for engineering chromophores displaying high two-photon absorption (TPA) in the near-IR region, as also confirmed experimentally. The ease of synthesis of quadrupolar derivatives thereof, combined with extraordinarly high TPA action cross sections (?TPA?f > 1500 GM), makes these heteroaromatic systems particularly attractive as diagnostic agents in 3D fluorescence imaging.Alexander von Humboldt foundation for a research fellowshipScopu

Nicotinamide-based supergelator self-assembling via asymmetric hydrogen bonding NH OC and H Br pattern for reusable, moldable and self-healable nontoxic fuel gels

Hypothesis Development of highly efficient low-molecular weight gelators (LMWGs) for safe energy storage materials is of great demand. Energy storage materials as fuel gels are often achieved by construction of hybrid organic frameworks capable of multiple noncovalent interactions in self-assembly, which allow tuning required properties at the molecular level by altering individual building blocks of the LMWG. However, LMWGs have limited rechargeable capability due to their chemical instability. Experiments We designed, synthesized and characterized a novel, bio-inspired chiral gemini amphiphile derivative 1 containing N-hexadecyl aliphatic tails from quaternized nicotinamide-based segment and bromide anion showing supergelation ability in water, alcohols, aprotic polar and aromatic solvents, with critical gel concentrations as low as 0.1 and 0.035 wt% in isopropanol and water, respectively. Findings Nanostructural architecture of the network depended on the solvent used and showed variations in size and shape of 1D nanofibers. Supergelation is attributed to a unique asymmetric NH⋯OC, H⋯Br− hydrogen bonding pattern between H-2 hydrogens from nicotinamide-based segment, amide functional groups from chiral trans-cyclohexane-1,2-diamide-based segment and bromide ions, supporting the intermolecular amide–amide interactions appearing across one strand of the self-assembly. Gels formed from 1 exhibit high stiffness, self-healing, moldable and colorable properties. In addition, isopropanol gels of 1 are attractive as reusable, shape-persistent non-toxic fuels maintaining the chemical structure with gelation efficiency for at least five consecutive burning cycles.This publication was jointly supported by Qatar University and Chemical Institute, Slovak Academy of Sciences Grant IRCC-2020-004 . The findings achieved herein are solely the work of the authors. This work was supported by the Slovak Research and Development Agency (grant no. APVV-17-0324 ) as well as by the Grant Agency of the Ministry of Education of the Slovak Republic (VEGA projects no. 1/0712/18 and 1/0145/20). P.H. also acknowledges the support from the European Union?s Horizon 2020 research and innovation programme under grant no. 810701 . J.O. acknowledges the Ministry of Education, Youth and Sports of the Czech Republic?DKRVO (RP/CPS/2020/003). Authors thank to Dr. Emil ?vajdlenka, Faculty of Pharmacy, Comenius University in Bratislava for HRMS measurements and Center for Advanced Materials and Gas Processing Center at Qatar University for support with facilities. The publication of this article was funded by the Qatar National Library.Scopu

An atomistic picture of the regeneration process in dye sensitized solar cells

A highly efficient mechanism for the regeneration of the cis-bis(isothiocyanato) bis(2,2'-bipyridyl-4,4'-dicarboxylato)-ruthenium (II) sensitizing dye (N3) by I- in acetonitrile has been identified by using molecular dynamics simulation based on density functional theory. Barrier-free complex formation of the oxidized dye with both I- and I-2(-), and facile dissociation of I-2(-) and I-3(-) from the reduced dye are key steps in this process. In situ vibrational spectroscopy confirms the reversible binding of I-2 to the thiocyanate group. Additionally, simulations of the electrolyte near the interface suggest that acetonitrile is able to cover the (101) surface of anatase with a passivating layer that inhibits direct contact of the redox mediator with the oxide, and that the solvent structure specifically enhances the concentration of I- at a distance which further favors rapid dye regeneration