Synthesis and Characterization of Hybrid Materials Derived from Conjugated Copolymers and Reduced Graphene Oxide.

In this study the preparation of hybrid materials based on reduced graphene oxide (rGO) and conjugated copolymers is reported. By tuning the number and arrangement of thiophenes in the main chain (indacenothiophene or indacenothienothiophene) and the nature of the polymer acceptor (difluoro benzothiadiazole or diketopyrrolopyrrole) semiconducting copolymers were synthesized through Stille aromatic coupling and characterized to determine their molecular characteristics. The graphene oxide was synthesized using the Staudenmaier method and was further modified to reduced graphene oxide prior to structural characterization. Various mixtures with different rGO quantities and conjugated copolymers were prepared to determine the optoelectronic, thermal and morphological properties. An increase in the maximum absorbance ranging from 3 to 6 nm for all hybrid materials irrespective of the rGO concentration, when compared to the pristine conjugated copolymers, was estimated through the UV-Vis spectroscopy indicating a differentiation on the optical properties. Through voltammetric experiments the oxidation and reduction potentials were determined and the calculated HOMO and LUMO levels revealed a decrease on the electrochemical energy gap for low rGO concentrations. The study indicates the potential of the hybrid materials consisting of graphene oxide and high band gap conjugated copolymers for applications related to organic solar cells.

Tissue Engineering Using Vascular Organoids From Human Pluripotent Stem Cell Derived Mural Cell Phenotypes.

Diffusion is a limiting factor in regenerating large tissues (100-200 µm) due to reduced nutrient supply and waste removal leading to low viability of the regenerating cells as neovascularization of the implant by the host is a slow process. Thus, generating prevascularized tissue engineered constructs, in which endothelial (ECs) and mural (MCs) cells, such as smooth muscle cells (SMCs), and pericytes (PCs), are preassembled into functional in vitro vessels capable of rapidly connecting to the host vasculature could overcome this obstacle. Toward this purpose, using feeder-free and low serum conditions, we developed a simple, efficient and rapid in vitro approach to induce the differentiation of human pluripotent stem cells-hPSCs (human embryonic stem cells and human induced pluripotent stem cells) to defined SMC populations (contractile and synthetic hPSC-SMCs) by extensively characterizing the cellular phenotype (expression of CD44, CD73, CD105, NG2, PDGFRß, and contractile proteins) and function of hPSC-SMCs. The latter were phenotypically and functionally stable for at least 8 passages, and could stabilize vessel formation and inhibit vessel network regression, when co-cultured with ECs in vitro. Subsequently, using a methylcellulose-based hydrogel system, we generated spheroids consisting of EC/hPSC-SMC (vascular organoids), which were extensively phenotypically characterized. Moreover, the vascular organoids served as focal starting points for the sprouting of capillary-like structures in vitro, whereas their delivery in vivo led to rapid generation of a complex functional vascular network. Finally, we investigated the vascularization potential of these vascular organoids, when embedded in hydrogels composed of defined extracellular components (collagen/fibrinogen/fibronectin) that can be used as scaffolds in tissue engineering applications. In summary, we developed a robust method for the generation of defined SMC phenotypes from hPSCs. Fabrication of vascularized tissue constructs using hPSC-SMC/EC vascular organoids embedded in chemically defined matrices is a significant step forward in tissue engineering and regenerative medicine.

Experimental and theoretical investigations on the optical and electrochemical properties of π-conjugated donor-acceptor-donor (DAD) compounds toward a universal model.

A series of nine (9) donor-acceptor-donor (DAD) π-conjugated small molecules were synthesized via palladium catalyzed Stille aromatic cross-coupling reactions by the combination of six (6) heterocycle building blocks (thiophene, furan, thiazole, 2,1,3-benzothiadiazole, 2,1,3-pyridinothiadiazole, thienothiadiazole) acting as electron donating (thiazole, furan, thiophene) and electron deficient (benzothiadiazole, pyridinethiadiazole, thienothiadiazole) units. These model compounds enable determining the correspondence between the theoretical and experimental optical and electrochemical properties for the first time, via Density Functional Theory (DFT), time-dependent DFT, UV-Vis spectroscopy, and cyclic voltammetry, accordingly. The obtained theoretical models can be utilized for the design and synthesis of new DAD structures with precise optical bandgaps, absorption maxima, and energy levels suitable for different optoelectronic applications.

Enhancement of the Power-Conversion Efficiency of Organic Solar Cells via Unveiling an Appropriate Rational Design Strategy in Indacenodithiophene- alt-quinoxaline π-Conjugated Polymers.

We report on the photovoltaic parameters, photophysical properties, optoelectronic properties, self-assembly, and morphology variations in a series of high-performance donor-acceptor (D-A) π-conjugated polymers based on indacenodithiophene and quinoxaline moieties as a function of the number-average molecular weight ([Formula: see text]), the nature of aryl substituents, and the enlargement of the polymer backbone. One of the most important outcome is that from the three optimization approaches followed to tune the chemical structure toward enhanced photovoltaic performance in bulk heterojunction solar cell devices with the fullerene derivative [6,6]-phenyl-C71-butyric acid methyl ester as the electron acceptor, the choice of the aryl substituent is the most efficient rational design strategy. Incorporation of thienyl rings as substituents versus phenyl rings accelerates the electron-hole extraction process to the respective electrode, despite the slightly lower recombination lifetime and, thus, improves the electrical performance of the device. Single-junction solar cells based on ThIDT-TQxT feature a maximum power-conversion efficiency of 7.26%. This study provides significant insights toward understanding of the structure-properties-performance relationship for D-A π-conjugated polymers in solid state, which provide helpful inputs for the design of next-generation polymeric semiconductors for organic solar cells with enhanced performance.

Beyond Donor-Acceptor (D-A) Approach: Structure-Optoelectronic Properties-Organic Photovoltaic Performance Correlation in New D-A1 -D-A2 Low-Bandgap Conjugated Polymers.

Low-bandgap near-infrared polymers are usually synthesized using the common donor-acceptor (D-A) approach. However, recently polymer chemists are introducing more complex chemical concepts for better fine tuning of their optoelectronic properties. Usually these studies are limited to one or two polymer examples in each case study so far, though. In this study, the dependence of optoelectronic and macroscopic (device performance) properties in a series of six new D-A1 -D-A2 low bandgap semiconducting polymers is reported for the first time. Correlation between the chemical structure of single-component polymer films and their optoelectronic properties has been achieved in terms of absorption maxima, optical bandgap, ionization potential, and electron affinity. Preliminary organic photovoltaic results based on blends of the D-A1 -D-A2 polymers as the electron donor mixed with the fullerene derivative [6,6]-phenyl-C71 -butyric acid methyl ester demonstrate power conversion efficiencies close to 4% with short-circuit current densities (J sc ) of around 11 mA cm-2 , high fill factors up to 0.70, and high open-circuit voltages (V oc s) of 0.70 V. All the devices are fabricated in an inverted architecture with the photoactive layer processed in air with doctor blade technique, showing the compatibility with roll-to-roll large-scale manufacturing processes.

Rational Design of High-Performance Wide-Bandgap (≈2 eV) Polymer Semiconductors as Electron Donors in Organic Photovoltaics Exhibiting High Open Circuit Voltages (≈1 V).

Systematic optimization of the chemical structure of wide-bandgap (≈2.0 eV) "donor-acceptor" copolymers consisting of indacenodithiophene or indacenodithieno[3,2-b]thiophene as the electron-rich unit and thieno[3,4-c]pyrrole-4,6-dione as the electron-deficient moiety in terms of alkyl side chain engineering and distance of the electron-rich and electron-deficient monomers within the repeat unit of the polymer chain results in high-performance electron donor materials for organic photovoltaics. Specifically, preliminary results demonstrate extremely high open circuit voltages (V oc s) of ≈1.0 V, reasonable short circuit current density (J sc ) of around 11 mA cm-2 , and moderate fill factors resulting in efficiencies close to 6%. All the devices are fabricated in an inverted architecture with the photoactive layer processed by doctor blade equipment, showing the compatibility with roll-to-roll large-scale manufacturing processes. From the correlation of the chemical structure-optoelectronic properties-photovoltaic performance, a rational guide toward further optimization of the chemical structure in this family of copolymers, has been achieved.

Systematic Analysis of Polymer Molecular Weight Influence on the Organic Photovoltaic Performance.

The molecular weight of an electron donor-conjugated polymer is as essential as other well-known parameters in the chemical structure of the polymer, such as length and the nature of any side groups (alkyl chains) positioned on the polymeric backbone, as well as their placement, relative strength, the ratio of the donor and acceptor moieties in the backbone of donor-acceptor (D-A)-conjugated polymers, and the arrangement of their energy levels for organic photovoltaic performance. Finding the "optimal" molecular weight for a specific conjugated polymer is an important aspect for the development of novel photovoltaic polymers. Therefore, it is evident that the chemistry of functional conjugated polymers faces major challenges and materials have to adopt a broad range of specifications in order to be established for high photovoltaic performance. In this review, the approaches followed for enhancing the molecular weight of electron-donor polymers are presented in detail, as well as how this influences the optoelectronic properties, charge transport properties, structural conformation, morphology, and the photovoltaic performance of the active layer.