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.

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.

Risk Factors for Weaning Failure in COVID-19 Patients.

Background: Data on risk factors associated with mechanical ventilation (MV) weaning failure among SARS-CoV2 ARDS patients is limited. We aimed to determine clinical characteristics associated with weaning outcome in SARS-CoV2 ARDS patients under MV. Objectives: To determine potential risk factors for weaning outcome in patients with SARS-CoV2 ARDS. Methods: A retrospective observational study was conducted in the ICUs of four Greek hospitals via review of the electronic medical record for the period 2020-2021. All consecutive adult patients were screened and were included if they fulfilled the following criteria: a) age equal or above 18 years, b) need for MV for more than 48 hours and c) diagnosis of ARDS due to SARS-CoV2 pneumonia or primary or secondary ARDS of other aetiologies. Patient demographic and clinical characteristics were recorded for the first 28 days following ICU admission. The primary outcome was weaning success defined as spontaneous ventilation for more than 48 hours. Results: A hundred and fifty eight patients were included; 96 SARS-CoV2 ARDS patients. SOFA score, Chronic Obstructive Pulmonary Disease (COPD) and shock were independently associated with the weaning outcome OR(95% CI), 0.86 (0.73-0.99), 0.27 (0.08-0.89) and 0.30 (0.14-0.61), respectively]. When we analysed data from SARS-CoV2 ARDS patients separately, COPD [0.18 (0.03-0.96)] and shock [0.33(0.12 - 0.86)] were independently associated with the weaning outcome. Conclusions: The presence of COPD and shock are potential risk factors for adverse weaning outcome in SARS-CoV2 ARDS patients.

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.