Polymeric Squaraine Dyes as Electron Donors in Bulk Heterojunction Solar Cells

A polysquaraine low band gap polymer was synthesized by Yamamoto coupling of a monomeric dibromo indolenine squaraine dye. The resulting polymer has a weight average molar mass in the order of Mw ~30.000-50.000 and a polydispersity of ca. 1.7 as determined by gel-permeation chromatography (GPC). The electronic properties of monomer and polymer were investigated by cyclic voltammetry, absorption and emission spectroscopy. Owing to exciton coupling the absorption bands of the polymer are red-shifted and strongly broadened compared to the monomer squaraine dye. Bulk heterojunction solar cells were prepared from blends of the polysquaraine with the fullerene derivative [6,6]-phenyl C61-butyric acid methyl ester (PCBM) in different weight ratios (1:3 to 1:1). The power conversion efficiencies under simulated AM 1.5 conditions yielded 0.45 % for these non-optimized systems. The external quantum efficiency (EQE) shows that the photoresponse spans the range from 300 to 850 nm, which illustrates the promising properties of this novel organic semiconductor as a low band gap donor material in organic photovoltaics.Comment: 10 pages, 7 figure

Aqueous Self-Sorting in Extended Supramolecular Aggregates

Self-organization and self-sorting processes are responsible for the regulation and control of the vast majority of biological processes that eventually sustain life on our planet. Attempts to unveil the complexity of these systems have been devoted to the investigation of the binding processes between artificial molecules, complexes or aggregates within multicomponent mixtures, which has facilitated the emergence of the field of self-sorting in the last decade. Since, artificial systems involving discrete supramolecular structures, extended supramolecular aggregates or gel-phase materials in organic solvents or—to a lesser extent—in water have been investigated. In this review, we have collected diverse strategies employed in recent years to construct extended supramolecular aggregates in water upon self-sorting of small synthetic molecules. We have made particular emphasis on co-assembly processes in binary mixtures leading to supramolecular structures of remarkable complexity and the influence of different external variables such as solvent and concentration to direct recognition or discrimination processes between these species. The comprehension of such recognition phenomena will be crucial for the organization and evolution of complex matter

Donor-acceptor type low band gap polymers: polysquaraines and related systems

In recent years, considerable effort has been directed towards the synthesis of conjugated polymers with low optical band gaps (Eg), since they show intrinsic electrical conductivity. One of the approaches towards the designing of such polymers is the use of strong donor and acceptor monomers at regular arrangements in the repeating units, which has limited success in many cases. An alternate strategy is the use of organic dyes, having inherently low HUMO-LUMO separation, as building blocks. Extension of conjugation in organic dyes is therefore expected to result in oligomers and polymers with near infrared absorption, which is a signature of low band gaps. Squaraine dyes are ideal candidates for this purpose due to their unique optical properties. This review highlights the recent developments in the area of donor-acceptor type low band gap polymers with special emphasis on polysquaraines

Control of crystallization in supramolecular soft materials engineering

As one class of the most important supramolecular functional materials, gels formed by low molecular weight gelators (LMWGs) have many important applications. The key important parameters affecting the in-use performance of a gel are determined by the hierarchical fiber network structures. Fiber networks consisting of weakly interacting multiple domains are commonly observed in gels formed by LMWGs. The rheological properties, particularly the elasticity, of a gel with such a fiber network are weak due to the weak interactions between the individual domains. As achieving desirable rheological properties of such a gel is practically relevant, in this work, we demonstrate the engineering of gels with such a type of fiber network by controlling crystallization of the gelator. Two example gels formed by a glutamic acid derivative in a non-ionic surfactant Tween 80 and in propylene glycol were engineered by controlling the thermodynamic driving force for crystallization. For a fixed gelator concentration, the thermodynamic driving force was manipulated by controlling the temperature for fiber crystallization. It was observed that there exists an optimal temperature at which a gel with maximal elasticity can be fabricated. This will hopefully provide guidelines for producing high performance soft materials by engineering their fiber network structures

Polymorphism, Fluorescence, and Optoelectronic Properties of a Borazine Derivative

EU, FRS-FNRS. Grant Numbers: 2.4.550.09, F.4.505.10.F, Belgian Government. Grant Numbers: P06-27, 09/14-023, University of Namur, FRIA, Italian National Research Council. Grant Number: PM.P04.010, European Commission. Grant Number: 238177, Belgian National Fund for Scientific Research (FNRS

Photoinduced energy- and electron-transfer from a photoactive coordination cage to bound guests.

In a coordination cage which contains an array of twelve naphthyl chromophores surrounding a central cavity, photoinduced energy or electron-transfer can occur from the chromophore array to the bound guest in supramolecular host/guest complexes

Light driven mesoscale assembly of a coordination polymeric gelator into flowers and stars with distinct properties

Control over the self-assembly process of porous organic–inorganic hybrids often leads to unprecedented polymorphism and properties. Herein we demonstrate how light can be a powerful tool to intervene in the kinetically controlled mesoscale self-assembly of a coordination polymeric gelator. Ultraviolet light induced coordination modulation via photoisomerisation of an azobenzene based dicarboxylate linker followed by aggregation mediated crystal growth resulted in two distinct morphological forms (flowers and stars), which show subtle differences in their physical properties

Solid-phase synthesis of C-terminal peptide amides using a photoremovable α-methylphenacylamido anchoring linkage

Polymer-supported solid-phase synthetic procedures have been developed for the synthesis of C-terminal peptide amides using a new photolytically removable a-methylphenacylamido anchoring linkage between the polymeric support and the growing peptide. The preparation of this new polymeric support involves a four-step polymer-analogous reaction starting from 2%-divinylbenzene-crosslinked polystyrene resin. The steps involved are (i) Friedel-Crafts reaction with 2-bromopropionyl chloride to give the 2-bromopropionyl resin, (ii) reaction of the 2-bromopropionyl resin with potassium phthalimide to give the phthalimidomethyl resin, (iii) hydrolysis with alcoholic potash to give the partially hydrolysed phthalamido resin and (iv) treatment with alcoholic HCl to give the 2-aminopropionyl resin. N-protected amino acids undergo coupling with this amino resin by the dicyclohexylcarbodiimide-mediated coupling. The acylated resins on irradiation at 350 nm in DMF released the attached carboxyl function in the C-terminal amide form. The mechanism of the photolytic deprotection involves a radical scission of the amide linkage adjacent to the phenacyl group. The synthetic utility of the new resin has been illustrated by the preparation of several N-protected amino acid amides and the C-terminal peptide amides, Boc-Pro-Val-NH2, Boc-Gly-Phe-Pro-NH2 and Boc-Leu-Ala-Gly-Val-NH2 in 70-74% yield

Solvent-Tuned Supramolecular Assembly of Fluorescent Catechol/Pyrene Amphiphilic Molecules

The synthesis and structuration of a novel low‐molecular‐weight amphiphilic catechol compound is reported. The combination of a hydrophilic tail containing a catechol unit and a pyrene‐based hydrophobic head favors solvent‐tuned supramolecular assembly. Formation of hollow nanocapsules/vesicles occurs in concentrated solutions of polar protic and nonprotic organic solvents, whereas a fibril‐like aggregation process is favored in water, even at low concentrations. The emission properties of the pyrene moiety allow monitoring of the self‐assembly process, which could be confirmed by optical and electronic microscopy. In organic solvents and at low concentrations, this compound remains in its nonassembled monomeric form. As the concentration increases, the aggregation containing preassociated pyrene moieties becomes more evident up to a critical micellar concentration, at which vesicle‐like structures are formed. In contrast, nanosized twist beltlike fibers are observed in water, even at low concentrations, whereas microplate structures appear at high concentrations. The interactions between molecules in different solvents were studied by using molecular dynamics simulations, which have confirmed different solvent‐driven supramolecular interactions.Fil: Nador, Fabiana Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina. Consejo Superior de Investigaciones Científicas; EspañaFil: Wnuk, Karolina. Consejo Superior de Investigaciones Científicas; EspañaFil: Roscini, Claudio. Consejo Superior de Investigaciones Científicas; EspañaFil: Solorzano, Ruben. Consejo Superior de Investigaciones Científicas; España. Universitat Autònoma de Barcelona; EspañaFil: Faraudo, Jordi. Consejo Superior de Investigaciones Científicas; EspañaFil: Ruiz Molina, Daniel. Consejo Superior de Investigaciones Científicas; EspañaFil: Novio, Fernando. Universitat Autònoma de Barcelona; España. Consejo Superior de Investigaciones Científicas; Españ