Modification of Electrode Surfaces by Self‐Assembled Monolayers of Thiol‐Terminated Oligo(Phenyleneethynylene)s

The wire‐like properties of four S‐(4‐{2‐[4‐(2‐phenylethynyl)phenyl]ethynyl}phenyl) thioacetate derivatives, PhC≡CC₆H₄C≡CC₆H₄SAc ( 1 ), H₂NC₆H₄C≡CC₆H₄C≡CC₆H₄SAc ( 2 ), PhC≡CC₆H₂(OMe)₂C≡CC₆H₄SAc ( 3 ) and AcSC₆H₄C≡CC₆H₄C≡CC₆H₄SAc ( 4 ) (Figure 1 ), all of which possess a high degree of conjugation along the oligo(phenyleneethynylene) (OPE) backbone, were investigated as self‐assembled monolayers (SAMs) on gold and platinum electrodes by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The redox probe [Fe(CN)₆]₄^? was used in both the CV and impedance experiments. The results indicate that the thiolates derived from thioacetate‐protected precursor molecules 1 and 2 form well‐ordered monolayers on a gold electrode, whereas SAMs derived from 3 and 4 exhibit randomly distributed pinholes. The electron tunnelling resistance and fractional coverage of SAMs of all four compounds were examined using electron tunnelling theory. The analysis of the results reveal that the well‐ordered SAMs of 1 and 2 exhibit higher charge‐transfer resistance in comparison to the defect‐ridden SAMs of 3 and 4 . The additional steric bulk offered by the methoxy groups in 3 is likely to prevent efficient packing within the SAM, leading to a microelectrode behaviour, when assembled on a gold electrode surface. The protected dithiol derivative 4 probably binds to the surface through both terminal groups which prevents dense packing and leads to the formation of a monolayer with randomly distributed pinholes. Atomic force microscopy (AFM) was used to examine the morphology of the monolayers, and height images gave root‐mean‐square (RMS) roughness′s which are in agreement with the proposed SAM structures.     

Bulk heterojunction solar cells based on self-assembling disc-shaped liquid crystalline material

In this article, effect of addition of disc-shaped liquid crystalline material, namely 2, 3, 6, 7, 10, 11-hexabutyloxytriphenylene, in poly (3-hexylthiophene): [6, 6]-phenyl-C61-butyric acid methyl ester containing bulk heterojunction (BHJ) solar cells has been investigated. These disc-shaped molecules organise into ordered columnar hexagonal structures through intermolecular π ? π interactions as monitored by polarised light optical microscopy. Current–voltage characteristics of the device prepared with liquid crystal layer exhibited a short-circuit current of 10.5 mA cm^?2 and a fill factor of 35%. The resultant power conversion efficiency (PCE) was 1.54%. The influence of varying the thickness of liquid crystal layer and annealing on these solar cells was also studied. The short circuit current and PCE of 12.9 mA cm^?2 and 2.3% was achieved for these BHJ solar cells containing self-organised discotic liquid crystals in the active layer under one sun condition after annealing.     

Impact of Multimeric Ferrocene-containing Cyclodecapeptide Scaffold on Host-Guest Interactions at a β-Cyclodextrin Covered Surface

Among non-covalent bonds, the host-guest interaction is an attractive way to attach biomolecules to solid surfaces since the binding strength can be tuned by the nature of host and guest partners or through the valency of the interaction. For that purpose, we synthesized cyclodecapeptide scaffolds exhibiting in a spatially controlled manner two independent domains enabling the multimeric presentation of guest molecules on one face and the other face enabling the potential grafting of a biomolecule of interest. In this work, we were interested in the β-cyclodextrin/ferrocene inclusion complex formed on β-CD monolayers functionalized surfaces. By using surface sensitive techniques such as quartz crystal microbalance and surface plasmon resonance, we quantified the influence of the guest valency on the stability of the inclusion complexes. The results show a drastic enhancement of the affinity with the gradual increase of guest valency. Considering that the sequential binding events are equal and independent, we applied the multivalent model developed by the Huskens group to extract intrinsic binding constants and an effective concentration of host.     

Luminscent graphene quantum dots for organic photovoltaic devices

Recent research in organic photovoltaic (OPV) is largely focused on developing low cost OPV materials such as graphene. However, graphene sheets (GSs) blended conjugated polymers are known to show inferior OPV characteristics as compared to fullerene adduct blended with conjugated polymer. Here, we demonstrate that graphene quantum dots blended with regioregular poly(3-hexylthiophene-2,5-diyl) or poly(2-methoxy-5-(2-ethylhexyloxy)-1,4phenylenevinylene) polymer results in a significant improvement in the OPV characteristics as compared to GSs blended conjugated polymers. This work has implications for inexpensive and efficient solar cells as well as organic light emitting diodes.     

Band gap narrowing and fluorescence properties of nickel doped SnO2 nanoparticles

Nickel-doped tin oxide nanoparticles (sub-5 nm size) with intense fluorescence emission behavior have been synthesized by sol-gel route. The structural and compositional analysis has been carried out by using XRD, TEM, FESEM and EDAX. The optical absorbance spectra indicate a band gap narrowing effect and it was found to increase with the increase in nickel concentration. The band gap narrowing at low dopant concentration (<5%) can be assigned to SnO₂−SnO_2−x alloying effect and for higher doping it may be due to the formation of defect sub-bands below the conduction band.     

Tuning the Photometric Properties of Ternary Sm3+ Complexes Involving Mixed-Ligands

This research article deals with the synthesis of ternary Sm³⁺ complexes with 6,8-dichlorochromone-3-carboxaldehyde through solution-precipitation method. The photometric properties of resultant complexes were tuned by coordinating N-donor heterocyclic ligands with Sm³⁺ ion. The emission spectra, obtained in the visible region have been studied. Under optical excitation of 370 nm, the complexes displayed characteristic Sm³⁺-centered emission peaks at?~?563, 600 and 647 nm in solution as well as in powder state. The complexes showed thermal stability up to 175 °C. The complexes delivered quantum yield as high as 7.91% and longest emission lifetime of 0.564 ms. The color coordinates of the complexes, located in deep orange (in solution) and red (in powder) spectral region, matched well with the Society of Motion Picture and Television Engineers and European Broadcasting Union. The properties of complexes have been investigated to a significant extent due to their easy synthesis and potential applications as orange-red light emitter in a wide range of photonic applications such as display devices, OLEDs, dashboards, optical systems.

     

Sonochemical degradation of martius yellow dye in aqueous solution

The sonolytic degradation of the textile dye martius yellow, also known as either naphthol yellow or acid orange 24, was studied at various initial concentrations in water. The degradation of the dye followed first-order kinetics under the conditions examined. Based on gas chromatographic results and sonoluminescence measurements of sonicated aqueous solutions of the dye, it is concluded that pyrolysis does not play a significant role in its degradation. The chromatographic identification of hydroxy added species indicates that an OH radical induced reaction is the main degradation pathway of the dye. Considering the non-volatility and surface activity of the dye, the degradation of the dye most probably takes place at the bubble/solution interface. The quantitative and qualitative formation of the degradation intermediates and final products were monitored using HPLC and ESMS. The analytical results suggest that the sonolytic degradation of the dye proceeds via hydroxylation of the aryl ring and also by C-N bond cleavage of the chromophoric ring, either through OH radical attack or through another unidentified process. The identification of various intermediates and end products also imply that the degradation of martius yellow proceeds through multiple reaction pathways. Total organic carbon (TOC) analyses of the dye solutions at various times following sonication revealed that sonolysis was effective in the initial degradation of the parent dye but very slow in achieving mineralization. The slow rate of mineralization is likely to be due to the inability of many of the intermediate products such as, the carboxylic acids, to accumulate at the bubble (air/water) interface and undergo decomposition due to their high water solubility (low surface activity).     

Catalytic cyclopropanation of olefins using copper(I) diphosphinoamines

Catalytic cyclopropanation reactions of olefins with ethyl diazoacetate were carried out using copper(I) diphosphinoamine (PPh₂)₂N(R) (R = ⁱPr, H, Ph and –CH₂–C₆H₄–CHCH₂) complexes at 40 °C in chloroform. High yields of the cyclopropanes were obtained in all cases. The rate of the reaction was influenced by the nuclearity of the complex and the binding mode of the ligand which was either bridging or chelating. Comparison of isostructural complexes shows that the rate follows the order R = ⁱPr > H > Ph, where R is the substituent on the N. However, cyclopropane formation versus dimerization of the carbene, and trans to cis ratios of cyclopropane was similar in all cases. The nearly identical selectivity for different products formed was indicative of a common catalytic intermediate. A labile “copper–olefin” complex which does not involve the phosphine or the counterion is the most likely candidate. The differences in the reaction rates for different complexes are attributed to differences in the concentration of the catalytically active species which are in equilibrium with the catalytically inactive copper–phosphinoamine complex. To test the hypothesis a diphosphinoamine polymer complexed to copper(I) was used as a heterogeneous catalyst. Leaching of copper(I) and deactivation of the catalyst confirmed the proposed mechanism.     

Structural investigations on Quinone Methides for understanding their properties in confined media

Encapsulation of 4−[(4′-hydroxy−3′,5′-dimethylphenyl)(aryl)-methylene]−2,6−dimethyl-cyclohexa−2,5−dienones (when aryl=4−hydroxyphenyl 1, 4−methoxyphenyl 2, 2,3,4-trimethoxy phenyl 3) by β-cyclodextrin is studied. The compound 2 is selectively encapsulated by β-cyclodextrin. The result is rationalised by analysing the structural parameters from the crystal structure of 1–3. The visible spectra of the compounds 2 and 3 at pH 9.0 show red shifts on the absorption maxima upon addition of cetyltrimethylammonium bromide (CTAB). For example, addition of a solution of CTAB to aqueous ethanolic solution of 2 at pH 9 causes shift of the absorption at 578–593 nm (Δλ_max=15 nm). The advantage of this observation is taken to use 2 and 3 to determine the critical micelle concentration of CTAB in basic medium.Graphical Abstract Structural investigations on quinone methides for understanding their properties in confined media Rupam J. Sarma, Andrei S. Batsanov, Ritu Kataky, Jubaraj B. Baruah      

Measuring microelastic properties of stratum corneum

We explore the compression moduli of a thin biological tissue through probe microscopy. The elastic modulus (E') of isolated stratum corneum is measured at varying depths through the use of an atomic force microscope (AFM) as well as a nano-indentor (Hysitron Triboscope). In addition, a nano-DMA is used to measure visco-elastic properties. Measurements on dry and hydrated stratum corneum show an order of magnitude difference in E' and the measured tandelta (E'/E') is seen to increase from approximately 0.1 to 0.25. In addition, extensive validation of the experiments is conducted with different indentation probes at different force ranges to reveal the effects of indentor geometry and indentation depth on the measured elastic modulus. The sensitivity of the measurements is tested with applying known treatments to stratum corneum and exploring their effects on biomechanical parameters.