On-surface synthesis of porous graphene nanoribbons containing nonplanar [14]annulene pores

The precise introduction of nonplanar pores in the backbone of graphene nanoribbon represents a great challenge. Here, we explore a synthetic strategy toward the preparation of nonplanar porous graphene nanoribbon from a predesigned dibromohexabenzotetracene monomer bearing four cove-edges. Successive thermal annealing steps of the monomers indicate that the dehalogenative aryl-aryl homocoupling yields a twisted polymer precursor on a gold surface and the subsequent cyclodehydrogenation leads to a defective porous graphene nanoribbon containing nonplanar [14]annulene pores and five-membered rings as characterized by scanning tunneling microscopy and noncontact atomic force microscopy. Although the C–C bonds producing [14]annulene pores are not achieved with high yield, our results provide new synthetic perspectives for the on-surface growth of nonplanar porous graphene nanoribbons.     

Structure absorption spectra correlation in a series of 2,6-dimethyl-4-arylpyrylium salts

A combined experimental and theoretical study of the absorption spectra of a group of closely related pyrylium perchlorates 1-11 are presented. Minor changes in the position of the substituents lead to drastic changes in the absorption spectra in this series of compounds. We have attempted to explain the observed changes using the x,y-band notation developed by Balaban and co-workers. Absorption spectra of all compounds are compared with results from time-dependent density functional theory (TDDFT) and Zerner's intermediate neglect of differential overlap (ZINDO/S) level calculations. Results of the calculations are in good agreement with experimental observations and an interesting correlation between Balaban's notations and the MO transitions are obtained for simple derivatives. It is suggested that for more complex systems such as alpha- and beta-naphthyl substituted systems, the empirical method is not appropriate.     

Solvent-based extraction optimisation for efficient ultrasonication-assisted ginsenoside recovery from Panax quinquefolius and P. sikkimensis cell suspension lines

The present study aims at developing an extraction protocol for efficient ginsenoside recovery from cell suspensions of Panax quinquefolius and P. sikkimensis. Methanol (100%, 70% and 30%), water (40°C, 90°C), water-saturated butanol and butanol-saturated water were compared for their ultrasonication-assisted ginsenoside retrieval efficacy. HPLC and HP-TLC analysis revealed 100% methanol as the best solvent for maximum retrieval of Rb (diol) and Rg (triol) ginsenosides (P. quinquefolius: Rb: 0.189, Rg: 3.163 mg/g DW; P. sikkimensis: Rb: 0.245, Rg: 4.073 mg/g DW), followed by water (90°C). Methanolic solutions, especially 70%, proved to be significant retrievers of Rg1 (1.812 and 1.327 mg/g DW in P. quinquefolius and P. sikkimensis), with poor Re recovery (0.328 and 0.342 mg/g DW). Water-saturated butanol also led to significant ginsenoside extraction (72.4% of content extracted by methanol), selectively in P. quinquefolius, with a less than 50% of total content extracted by methanol, in P. sikkimensis.     

Light-induced charge separation and photocatalytic hydrogen evolution from water using Ru(II)Pt(II)-based molecular devices: effects of introducing additional donor and/or acceptor sites

In our hopes to improve the photocatalytic efficiency of photo-hydrogen-evolving molecular devices, several new dyads and triads possessing a photosensitizing Ru(bpy)(phen)(2)(2+) (or Ru(phen)(3)(2+)) chromophore (abbreviated as Ru(II)) attached to both/either a phenothiazine moiety (abbreviated as Phz) and/or H(2)-evolving PtCl(2)(bpy) units (abbreviated as Pt), such as Phz-Ru(II)-Pt2 (triad), Ru(II)-Pt2 (dyad), and Ru(II)-Pt3 (dyad), were synthesized and their basic properties together with the photo-hydrogen-evolving characteristics were investigated in detail. The (3)MLCT phosphorescence from the Ru(II) moiety in these systems is substantially quenched due to the highly efficient photoinduced electron transfer (PET). Based on the electrochemical studies, the driving forces for the PET were estimated as -0.07 eV for Phz-Ru(II)-Pt2, -0.24 eV for Ru(II)-Pt2, and -0.22 eV for Ru(II)-Pt3, revealing the exergonic character of the PET in these systems. Luminescence lifetime studies revealed the existence of more than two decay components, indicative of a contribution of multiple PET processes arising from the presence of at least two different conformers in solution. The major luminescence decay components of the hybrid systems [τ(1) = 6.5 ns (Ru(II)-Pt2) and τ(1) = 1.04 ns (Phz-Ru(II)-Pt2) in acetonitrile] are much shorter than those of Phz-free/Pt-free Ru(bpy)(phen)(2)(2+) derivatives. An important finding is that the triad Phz-Ru(II)-Pt2 affords a quite long-lived charge separated (CS) state (τ(CS) = 43 ns), denoted as Phz(+)˙-Ru(Red)-Pt2, as a result of reductive quenching of the triplet excited state of Ru(bpy)(phen)(2)(2+) by the tethering Phz moiety, where Ru(Red) denotes Ru(bpy)(phen)(2)(+). Moreover, the lifetime of Phz(+)˙-Ru(Red)-Pt2 was observed to be much longer than that of Phz(+)˙-Ru(Red). The photocatalytic H(2) evolution from water driven by these systems was examined in an aqueous acetate buffer solution (pH 5.0) containing 4-19% dimethylsulfoxide (solubilising reagent) in the presence of EDTA as a sacrificial electron donor. Dyads Ru(II)-Pt2 and Ru(II)-Pt3 were found to exhibit improved photo-hydrogen-evolving activity compared to the heterodinuclear Ru-Pt dyads developed so far in our group. On the other hand, almost no catalytic activity was observed for Phz-Ru(II)-Pt2 in spite of the formation of a strongly reducing Ru(Red) site (Phz(+)˙-Ru(Red)-Pt2), indicating that the electron transfer from the photogenerated Ru(Red) unit to the PtCl(2)(bpy) unit is not favoured presumably due to the slow electron transfer rate in the Marcus inverted region.     

Tailoring Magnetic Features in Zigzag-Edged Nanographenes by Controlled Diels–Alder Reactions

Nanographenes (NGs) with tunable electronic and magnetic properties have attracted enormous attention in the realm of carbon-based nanoelectronics. In particular, NGs with biradical character at the ground state are promising building units for molecular spintronics. However, most of the biradicaloids are susceptible to oxidation under ambient conditions and photolytic degradation, which hamper their further applications. Herein, we demonstrated the feasibility of tuning the magnetic properties of zigzag-edged NGs in order to enhance their stability via the controlled Diels–Alder reactions of peri-tetracene ( 4-PA ). The unstable 4-PA (y₀=0.72; half-life, t_1/2=3 h) was transformed into the unprecedented benzo-peri-tetracenes ( BPTs ) by a one-side Diels–Alder reaction, which featured a biradical character at the ground state (y₀=0.60) and exhibited remarkable stability under ambient conditions for several months. In addition, the fully zigzag-edged circumanthracenes ( CAs ) were achieved by two-fold or stepwise Diels–Alder reactions of 4-PA , in which the magnetic properties could be controlled by employing the corresponding dienophiles. Our work reported herein opens avenues for the synthesis of novel zigzag-edged NGs with tailor-made magnetic properties.     

<Emphasis Type="Italic">Atropa belladonna</Emphasis> Hairy Roots: Orchestration of Concurrent Oxidation and Reduction Reactions for Biotransformation of Carbonyl Compounds

The biotransformation potential of a selected Atropa belladonna hairy root clone (AB-09) had been evaluated with regard to three different aromatic carbonyl compounds, i.e., 3,4,5-trimethoxybenzaldehyde (1), 3,4,5-trimethoxyacetophenone (2), and 3,4,5-trimethoxy benzoic acid (3). The results demonstrated for the first time the untapped potentials of the selected hairy root clone to perform simultaneous oxidation (34.49%) and reduction (32.68%) of 3,4,5-trimethoxy benzaldehyde (1) into 3,4,5-trimethoxy benzoic acid (3), and 3,4,5-trimethoxy benzyl alcohol (4), respectively, without any intermediate separation or addition of reagents. The same hairy root clone also demonstrated reduction (<5%) of a 3,4,5-trimethoxyacetophenone (2) into a secondary alcohol, i.e., 1-(3,4,5-trimethoxyphenyl) ethanol (5), while in the case of aromatic carboxylic acid substrate (3), no biotransformation could be obtained under the similar conditions. The current observations revealed oxidation and reduction of the formyl group of the aromatic ring, and only reduction of the carbonyl group of acetophenone through the specific hairy root clone. The concurrent oxidation and reduction reactions by the selected hairy root clone highlight the importance of this study, which, as per our observations, is the first of its kind relating the hairy root culture of A. belladonna.     

Highly Oxidized States of Phthalocyaninato Terbium(III) Multiple-Decker Complexes Showing Structural Deformations,Biradical Properties and Decreases in Magnetic Anisotropy

Presented here is a comprehensive study of highly oxidized multiple-decker complexes composed of Tb^III and Cd^II ions and two to five phthalocyaninato ligands, which are stabilized by electron-donating n-butoxy groups. From X-ray structural analyses, all the complexes become axially compressed upon ligand oxidation, resulting in bowl-shaped distortions of the ligands. In addition, unusual coexistence of square antiprism and square prism geometries around metal ions was observed in +4e charged species. From paramagnetic ¹H NMR studies on the resulting series of triple, quadruple and quintuple-decker complexes, ligand oxidation leads to a decrease in the magnetic anisotropy, as predicted from theoretical calculations. Unusual paramagnetic shifts were observed in the spectra of the +2e charged quadruple and quintuple-decker complexes, indicating that those two species are actually unexpected triplet biradicals. Magnetic measurements revealed that the series of complexes show single-molecule magnet properties, which are controlled by the multi-step redox induced structural changes.     

Platinum(II)-based hydrogen-evolving catalysts linked to multipendant viologen acceptors: experimental and DFT indications for bimolecular pathways

Three new [PtCl(2)(bpy)] derivatives tethered to 2, 4, and 6 dicationic viologen moieties, [PtCl(2)(MV2)](4+) (1), [PtCl(2)(MV4)](8+) (2), and [PtCl(2)(MV6)](12+) (3), have been synthesized (MV2(4+)=5-ethoxycarbamoyl-5'-(N-R(1)-carbamoyl)-2,2'-bipyridine, MV4(8+)=5,5'-bis(N-R(1)-carbamoyl)-2,2'-bipyridine, and MV6(12+)=5,5'-bis(N-R(2)-carbamoyl)-2,2'-bipyridine, in which R(1)=Asp(NH-VG)-NH-VG, R(2)=Asp(NH-VG)-Asp(NH-VG)-NH-VG, and VG=-(CH(2))(2)-(+)NC(5)H(4)-C(5)H(4)N(+)-CH(3)). In spite of the higher charge storage capacity of 2 and 3 due to the higher number of acceptor groups (VG groups), compound 1 with the lowest number of VG tethers has turned out to exhibit an outstanding catalytic performance towards the hydrogen evolution from water. Quantitative analysis of UV/Vis-NIR absorption spectral changes during the photolysis for 2 and 3 reveal that approximately 2 electrons per molecule are stored over the acceptor groups during the photolysis, and the storage events saturate after 20 min. As for 1, the total number of electrons stored per molecule increases once during the initial 10 min and then abruptly decreases down to around 0.1 electrons per molecule at 20 min, during which the storage is maximized at 10-20 min with 0.6-0.7 electrons stored per molecule, thereby indicating that the rates of radical formation and consumption are balanced during the photochemical hydrogen evolution reaction. The electrical conductivity measurements reveal that ion-pair adducts (adducts with PF(6)(-) ions in solution) are formed by 2 and 3 but are not given by 1 under the catalysis conditions. These, together with the results of molecular mechanics calculations, reveal that stack of two [PtCl(2)(bpy)] units becomes unfavorable as the number of sterically bulky and highly charged VG units per molecule increases. We have therefore concluded that dimerization that leads to the formation of a Pt-Pt association is a key step in the effective catalytic enhancement with [PtCl(2)(bpy)]-type catalysts.