1,352 research outputs found
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
Light driven mesoscale assembly of a coordination polymeric gelator into flowers and stars with distinct properties
Control over the self-assembly process of porous organicâinorganic 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
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
Solvent-Tuned Supramolecular Assembly of Fluorescent Catechol/Pyrene Amphiphilic Molecules
The synthesis and structuration of a novel lowâmolecularâweight amphiphilic catechol compound is reported. The combination of a hydrophilic tail containing a catechol unit and a pyreneâbased hydrophobic head favors solventâtuned supramolecular assembly. Formation of hollow nanocapsules/vesicles occurs in concentrated solutions of polar protic and nonprotic organic solvents, whereas a fibrilâlike aggregation process is favored in water, even at low concentrations. The emission properties of the pyrene moiety allow monitoring of the selfâassembly 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 vesicleâlike 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 solventâdriven supramolecular interactions.Fil: Nador, Fabiana Gabriela. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - BahĂa Blanca. Instituto de QuĂmica del Sur. Universidad Nacional del Sur. Departamento de QuĂmica. Instituto de QuĂmica del Sur; Argentina. Consejo Superior de Investigaciones CientĂficas; EspañaFil: Wnuk, Karolina. Consejo Superior de Investigaciones CientĂficas; EspañaFil: Roscini, Claudio. Consejo Superior de Investigaciones CientĂficas; EspañaFil: Solorzano, Ruben. Consejo Superior de Investigaciones CientĂficas; España. Universitat AutĂČnoma de Barcelona; EspañaFil: Faraudo, Jordi. Consejo Superior de Investigaciones CientĂficas; EspañaFil: Ruiz Molina, Daniel. Consejo Superior de Investigaciones CientĂficas; EspañaFil: Novio, Fernando. Universitat AutĂČnoma de Barcelona; España. Consejo Superior de Investigaciones CientĂficas; Españ
Self-Assembly of Optical Molecules with Supramolecular Concepts
Fabrication of nano-sized objects is one of the most important issues in nanoscience and nanotechnology. Soft nanomaterials with flexible properties have been given much attention and can be obtained through bottom-up processing from functional molecules, where self-assembly based on supramolecular chemistry and designed assembly have become crucial processes and techniques. Among the various functional molecules, dyes have become important materials in certain areas of nanotechnology and their self-assembling behaviors have been actively researched. In this short review, we briefly introduce recent progress in self-assembly of optical molecules and dyes, based mainly on supramolecular concepts. The introduced examples are classified into four categories: self-assembly of (i) low-molecular-weight dyes and (ii) polymeric dyes and dye self-assembly (iii) in nanoscale architectures and (iv) at surfaces
Energy Level Modulation of HOMO, LUMO, and BandâGap in Conjugated Polymers for Organic Photovoltaic Applications
To devise a reliable strategy for achieving specific HOMO and LUMO energy level modulation via alternating donorâacceptor monomer units, we investigate a series of conjugated polymers (CPs) in which the electron withdrawing power of the acceptor group is varied, while maintaining the same donor group and the same conjugated chain conformation. Through experiment and DFT calculations, good correlation is identified between the withdrawing strength of the acceptor group, the HOMO and LUMO levels, and the degree of orbital localization, which allows reliable design principles for CPs. Increasing the acceptor strength results in an enhanced charge transfer upon combination with a donor monomer and a more pronounced decrease of the LUMO level. Moreover, while HOMO states remain delocalized along the polymer chain, LUMO states are strongly localized at specific bonds within the acceptor group. The degree of LUMO localization increases with increasing polymer length, which results in a further drop of the LUMO level and converges to its final value when the number of repeat units reaches the characteristic conjugation length. Based on these insights we designed PBT8PT, which exhibits 6.78% power conversion efficiency after device optimization via the additive assisted annealing, demonstrating the effectiveness of our predictive design approach. A strong acceptor lowers both the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of conjugated polymers (CPs), ultimately producing a narrowed bandâgap. The energy level difference between the CP and the constituent monomers converge to a constant value, providing an energy level prediction tool. Organic photovoltaic performance is correlated with the CP's energy levels, and a 6.78% power conversion efficiency is achieved.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/96311/1/adfm_201201385_sm_suppl.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/96311/2/439_ftp.pd
Increasing Photovoltaic Performance of an Organic Cationic Chromophore by Anion Exchange
A symmetrical cyanine dye chromophore is modified with different counteranions to study the effect on crystal packing, polarizability, thermal stability, optical properties, light absorbing layer morphology, and organic photovoltaic (OPV) device parameters. Four sulfonate-based anions and the bulky bistriflylimide anion are introduced to the 2-[5-(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)-1,3-pentadien-1-yl]-1,3,3-trimethyl-3H-indolium chromophore using an Amberlyst A26 (OHâ form) anion exchanger. Anionic charge distribution clearly correlates with device performance, whereby an average efficiency of 2% was reached in a standard bilayer organic solar. Evidence is given that the negative charge of the anion distributed over a large number of atoms is significantly more important than the size of the organic moieties of the sulfonate charge carrying group. This provides a clear strategy for future design of more efficient cyanine dyes for OPV applications.The authors thank Dr. Matthias Nagel (Empa) for suggestions and
Dr. Mohammed Makha (Empa) for his help with the thermal evaporation
techniques. The use of the Scanning Probe Microscopy User Laboratory
at Empa is gratefully acknowledged. The authors thank the Swiss
National Science Foundation for financial support under grant number
160116. This project has also received funding from the Universidad
Carlos III de Madrid, the European Unionâs Seventh Framework Program
for research, technological development and demonstration under
grant agreement No. 600371, el Ministerio de EconomĂa, Industria y
Competitividad (COFUND2014-51509), el Ministerio de EducaciĂłn,
cultura y Deporte (CEI-15-17), and Banco Santander
- âŠ