Self-Assembled Organic Materials for Photovoltaic Application

Combining Step-Growth and Chain-Growth Polymerizations in One Pot: Light-Induced Fabrication of Conductive Nanoporous PEDOT-PCL Scaffold

A novel method based on light-induced fabrication of a poly (3,4-ethylenedioxythiophene)-polycaprolactone (PEDOT-PCL) scaffold using phenacyl bromide (PAB) as a single-component photoinitiator is presented. HBr released from the step-growth polymerization of EDOT is utilized as an in situ catalyst for the chain-growth polymerization of ε-caprolactone. Detailed investigations disclose the formation of a self-assembled nanoporous electroconductive scaffold (1.2 mS cm-1 ). Fluorescence emission spectra of the fabricated scaffold exhibit a mixed solvatochromic behavior, indicating specific interactions between the self-assembled scaffold and solvents with varying polarities, as evidenced by transmission electron microscopy (TEM). Moreover, the same light-induced technique can also be applied for bulk photopolymerization showcasing the versatility and wide-ranging scope of the originated method. In brief, this study introduces a novel approach for light-induced polymerization reactions that is merging step-growth and chain-growth mechanisms. This innovative approach is promising to facilitate in situ polymerization of monomers possessing diverse functionalities.

Nanoscale self-assembly: concepts, applications and challenges

Self-assembly offers unique possibilities for fabricating nanostructures, with different morphologies and properties, typically from vapour or liquid phase precursors. Molecular units, nanoparticles, biological molecules and other discrete elements can spontaneously organise or form via interactions at the nanoscale. Currently, nanoscale self-assembly finds applications in a wide variety of areas including carbon nanomaterials and semiconductor nanowires, semiconductor heterojunctions and superlattices, the deposition of quantum dots, drug delivery, such as mRNA-based vaccines, and modern integrated circuits and nanoelectronics, to name a few. Recent advancements in drug delivery, silicon nanoelectronics, lasers and nanotechnology in general, owing to nanoscale self-assembly, coupled with its versatility, simplicity and scalability, have highlighted its importance and potential for fabricating more complex nanostructures with advanced functionalities in the future. This review aims to provide readers with concise information about the basic concepts of nanoscale self-assembly, its applications to date, and future outlook. First, an overview of various self-assembly techniques such as vapour deposition, colloidal growth, molecular self-assembly and directed self-assembly/hybrid approaches are discussed. Applications in diverse fields involving specific examples of nanoscale self-assembly then highlight the state of the art and finally, the future outlook for nanoscale self-assembly and potential for more complex nanomaterial assemblies in the future as technological functionality increases.

The Importance of Spin State in Chiral Supramolecular Electronics

The field of spintronics explores how magnetic fields can influence the properties of organic and inorganic materials by controlling their electron’s spins. In this sense, organic materials are very attractive since they have small spin-orbit coupling, allowing long-range spin-coherence over times and distances longer than in conventional metals or semiconductors. Usually, the small spin-orbit coupling means that organic materials cannot be used for spin injection, requiring ferromagnetic electrodes. However, chiral molecules have been demonstrated to behave as spin filters upon light illumination in the phenomenon described as chirality-induced spin selectivity (CISS) effect. This means that electrons of certain spin can go through chiral assemblies of molecules preferentially in one direction depending on their handedness. This is possible because the lack of inversion symmetry in chiral molecules couples with the electron’s spin and its linear momentum so the molecules transmit the one preferred spin. In this respect, chiral semiconductors have great potential in the field of organic electronics since when charge carriers are created, a preferred spin could be transmitted through a determined handedness structure. The exploration of the CISS effect in chiral supramolecular semiconductors could add greatly to the efforts made by the organic electronics community since charge recombination could be diminished and charge transport improved when the spins are preferentially guided in one specific direction. This review outlines the advances in supramolecular chiral semiconductors regarding their spin state and its influence on the final electronic properties.

Electrochemical and Spectroelectrochemical Studies on the Reactivity of Perimidine-Carbazole-Thiophene Monomers towards the Formation of Multidimensional Macromolecules versus Stable π-Dimeric States

During research on cross-linked conducting polymers, double-functionalized monomers were synthesized. Two subunits potentially able to undergo oxidative coupling were used—perimidine and, respectively, carbazole, 3,6-di(hexylthiophene)carbazole or 3,6-di(decyloxythiophene)carbazole; alkyl and alkoxy chains as groups supporting molecular ordering and 14H-benzo[4,5]isoquinone[2,1-a]perimidin-14-one segment promoting CH⋯O interactions and π–π stacking. Electrochemical, spectroelectrochemical, and density functional theory (DFT) studies have shown that potential-controlled oxidation enables polarization of a specific monomer subunit, thus allowing for simultaneous coupling via perimidine and/or carbazole, but mainly leading to dimer formation. The reason for this was the considerable stability of the dicationic and tetracationic π-dimers over covalent bonding. In the case of perimidine-3,6-di(hexylthiophene)carbazole, the polymer was not obtained due to the steric hindrance of the alkyl substituents preventing the coupling of the monomer radical cations. The only linear π-conjugated polymer was obtained through di(decyloxythiophene)carbazole segment from perimidine-di(decyloxythiophene)-carbazole precursor. Due to the significant difference in potentials between subsequent oxidation states of monomer, it was impossible to polarize the entire molecule, so that both directions of coupling could be equally favored. Subsequent oxidation of this polymer to polarize the side perimidine groups did not allow further crosslinking, because rather the π–π interactions between these perimidine segments dominate in the solid product.

Spin Transport in Organic Molecules

Because of the considerable advantages of functional molecules as well as supramolecules, such as the low cost, light weight, flexibility, and large area preparation via the solution method, molecular electronics has grown into an active and rapidly developing research field over the past few decades. Beyond those well-known advantages, a very long spin relaxation time of π-conjugated molecules, due to the weak spin-orbit coupling, facilitates a pioneering but fast-growing research field, known as molecular spintronics. Recently, a series of sustained progresses have been achieved with various π-conjugated molecular matrixes where spin transport is undoubtedly an important point for the spin physical process and multifunctional applications. Currently, most studies on spin transport are carried out with a molecule-based spin valve, which shows a typical geometry with a thin-film molecular layer sandwiched between two ferromagnetic electrodes. In such a device, the spin transport process has been demonstrated to have a close correlation with spin relaxation time and charge carrier mobility of π-conjugated molecules. In this review, the recent advances of spin transport in these two aspects have been systematically summarized. Particularly, spin transport in π-conjugated molecular materials, considered as promising for spintronics development, have also been highlighted, including molecular single crystal, cocrystal, solid solution as well as other highly ordered supramolecular structures.

An Easy Route to Wettability Changes of Polyethylene Terephthalate⁻Silicon Oxide Substrate Films for High Barrier Applications, Surface-Modified with a Self-Assembled Monolayer of Fluoroalkylsilanes

Inorganic⁻organic multilayer films consisting of polymers coated with thin inorganic oxidic layers (e.g., SiOx) ensure very high barrier performances against gas and vapor permeation, what makes them packaging materials suitable for sophisticated technical applications, including the encapsulation of photovoltaic devices or quantum dots, barrier films for optical displays, and transparent greenhouse screens. In these fields, surface coating or texturing of the multilayer protective films are effective technologies to improve their self-clean ability, thus reducing the required maintenance and ensuring longer durability and better performances. In this work, we used the self-assembled monolayer (SAM) technique to modify the surface and wetting properties of commercial polyethylene terephthalate-silicon oxide substrate (PET-SiOx) films developed for technical applications requiring a combined high barrier and transparency. The selected surface modifier was the 1H,1H,2H,2H-per-fluorodecyltrichlorosilane (FDTS). The reagent mixture composition was optimized for the lowest water and oil wettability, as well as the highest self-cleaning capacity and performance stability. In particular, for the used PET-SiOx film the best FDTS/film surface for both the lowest water and oil wettability was found to be equal to 26.5 mM/dm², which changes the surface behavior from very hydrophilic (static water contact angle (CAw) = 21.5°) to hydrophobic (CAw = 101°), and gives a significant increment of the static oil contact angle (CAo) from 27° to 60°. Interestingly, the results demonstrated that the SAM reaction occurred also on the uncoated the PET side. After the SAM treatment, a small increase of the water vapor permeability is observed, probably due to a crack or defect onset of the SiOx coating of the SAM modified films. On this point, atomic force measurements demonstrated an increment of the SiOx coating layer roughness after the SAM treatment execution. Finally, the transparency changes of the SAM treated films, measured in the wavelength range 400⁻800 nm, were always small, so that the results were acceptable for the films' use in applications where high transparency is required.

2-Hydroxy-N'-((Thiophene-2-yl)methylene)benzohydrazide: Ultrasound-Assisted Synthesis and Corrosion Inhibition Study

2-Hydroxy-N'-((thiophene-2-yl)methylene)benzohydrazide (HTMBH) was synthesized by conventional method as well as by ultrasonication (US). The ultrasound-assisted synthesis of HTMBH was found to have good yield and be more eco-friendly compared to the conventional method of synthesis. The synthesized compound HTMBH was characterized by Fourier transform infrared, 1H NMR, and CHN analyses. The corrosion inhibition behavior of HTMBH was investigated using gravimetric and electrochemical methods in 0.5 M H2SO4. The thermodynamic adsorption parameters revealed that HTMBH was adsorbed on the mild steel surface in both ways, physically and chemically, although physisorption is predominant. The study of activation parameters revealed that it is the increase in activation energy that is a prominent factor to lower the corrosion rate in acid medium. Atomic force microscopy analysis is also carried out to investigate the effect of HTMBH on the surface of mild steel surface in acid solution. The contact angle measurement showed decreased affinity of mild steel surface for acid solution containing HTMBH. The results obtained from all of these methods showed good consistency.

Green synthesis and corrosion inhibition study of 2-amino-N′-((thiophen-2-yl)methylene)benzohydrazide

2-Amino-N′-((thiophen-2-yl)methylene)benzohydrazide (ATMBH) was synthesized by a conventional method, as well as by microwave (MW) irradiation.

π-Choreography in aromatic ammonium formate solids

Eight novel benzylammonium formate complexes are combed for evidence suggesting “π-stacking” interactions, and are compared with similar published lamellar structures.

Noncovalent Interactions in the Catechol Dimer

Noncovalent interactions play a significant role in a wide variety of biological processes and bio-inspired species. It is, therefore, important to have at hand suitable computational methods for their investigation. In this paper, we report on the contribution of dispersion and hydrogen bonds in both stacked and T-shaped catechol dimers, with the aim of delineating the respective role of these classes of interactions in determining the most stable structure. By using second-order Møller⁻Plesset (MP2) calculations with a small basis set, specifically optimized for these species, we have explored a number of significant sections of the interaction potential energy surface and found the most stable structures for the dimer, in good agreement with the highly accurate, but computationally more expensive coupled cluster single and double excitation and the perturbative triples (CCSD(T))/CBS) method.

Refractive-Index Tuning of Highly Fluorescent Carbon Dots

In this manuscript, we report the refractive-index (RI) modulation of various concentrations of nitrogen-doped carbon dots (N@C-dots) embedded in poly(vinyl alcohol) (PVA) polymer. The dispersion and size distribution of N@C-dots embedded within PVA have been investigated using electron microscopy. The RI of PVA-N@C-dots can be enhanced by increasing the doping concentration of highly fluorescent C-dots (quantum yield 44%). This is demonstrated using ultraviolet-visible (UV-visible), photoluminscence, Raman, and Fourier transform infrared (FTIR) spectroscopy measurements. The Mie scattering of light on N@C-dots was applied for developing the relationship between RI tuning and absorption cross section of N@C-dots. The extinction cross section of N@C-dot thin films can be rapidly enhanced by either tuning the RI or increasing the concentration of N@C-dots. The developed method can be used as effective RI contrast for various applications such as holography creation and bioimaging.

Synthesis of Polymer Nanocomposites Based on [Methyl Cellulose](1-x):(CuS)x (0.02 M ≤ x ≤ 0.08 M) with Desired Optical Band Gaps

In this paper, the sample preparation of polymer nanocomposites based on methyl cellulose (MC) with small optical bandgaps has been discussed. Copper monosulfide (CuS) nanoparticles have been synthesized from the sodium sulphide (Na₂S) and copper chloride (CuCl₂) salts. Distinguishable localized surface resonance plasmon (LSRP) absorption peaks for CuS nanoparticles within the 680⁻1090 nm scanned wavelength range were observed for the samples. An absorption edge (Ed) was found to be widely shifted to a lower photon energy region. A linear relationship between the refractive index of the samples and the CuS fraction was utilized to describe the distribution of the particle. The optical bandgap of MC was reduced from 6.2 to 2.3 eV upon the incorporation of 0.08 M of CuS nanoparticles. The optical dielectric loss, as an alternative method, was used successfully to estimate the optical bandgap. Moreover, the electronic transition type was identified by using Tauc's extrapolation method. The plots of the optical dielectric constant and energy bandgap as a function of the CuS concentration were utilized to examine the validity of the Penn model. For the nanocomposite samples, the Urbach energy was found to be increased, which can be evidence for a large possible number of bands-to-tail and tail-to-tail transitions. However, from the X-ray diffraction (XRD) analysis, it was also found that the synthesized CuS nanoparticles disrupted the crystallinity phase of the MC polymer. Finally, fourier transform infrared (FTIR) spectroscopy for the samples was also performed. Significant decreases of transmittance intensity as well as band shifting in the FTIR spectra were observed for the doped samples.