Optoelectronic Properties of A-π-D-π-A Thiophene-Based Materials with a Dithienosilole Core: An Experimental and Theoretical Study

Two A-π-D-π-A thiophene-based small molecules with a central dithienosilole core and dicyanovinyl (DCV) end groups were synthesized. These compounds differ only by the presence of alkyl and alkylsulfanyl chains, respectively, on the thiophene beta positions. Computational data together with the spectroscopic and electrochemical findings (obtained by means of absorption, steady-state/time-resolved emission techniques, and cyclic voltammetry) revealed that both molecules possess low electronic and optical band gaps, broad absorption spectra, and good stability both in p and n-doping states, which make them suitable for optoelectronic applications. In both compounds, the HOMO-LUMO transition involves an intramolecular charge transfer from the electron-donor dithienosilole unit to the two terminal electron-acceptor DCV groups. A marked positive emission solvatochromism was observed for both molecules and was interpreted on the basis of the symmetry breaking in the S₁ excited state. The two synthesized compounds were also compared to their shorter precursors and to similar oligothiophenes to understand how the nature of the building block influences the characteristics of the final materials. Furthermore, it was possible to better understand the contribution of the sulfur atom in modulating the optical properties of the small molecules studied.

Π-Stacking Signature in NMR Solution Spectra of Thiophene-Based Conjugated Polymers

Studies on conjugated polymers seldom report on their NMR characterization in solution. This paper shows how NMR experiments, both ¹H NMR and routine 2D NMR spectra, can help in gaining a further insight into the aggregation behavior of conjugated polymers and could be used to flank the more employed solid-state NMR and other spectroscopy and microscopy techniques in the understanding of the aggregation processes. NMR spectroscopy allows distinguishing, within the class of poorly solvatochromic conjugated polymers, those highly prone to form π-stacked aggregates from the ones that have a low tendency toward π-stacking.

Synthesis and Antimicrobial Studies of New Antibacterial Azo-Compounds Active against Staphylococcus aureus and Listeria monocytogenes

Some novel (phenyl-diazenyl)phenols (4a–m) were designed and synthesized to be evaluated for their antibacterial activity. Starting from an active previously-synthesized azobenzene chosen as lead compound, we introduced some modifications and optimization of the structure, in order to improve solubility and drug conveyance. Structures of all newly-synthesized compounds were confirmed by ¹H nuclear magnetic resonance (NMR), mass spectrometry, and UV-Vis spectroscopy. Antibacterial activity of the new compounds was tested with the dilution method against the bacteria strains Listeria monocytogenes, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa PAO1. All the compounds were selectively active against Gram-positive bacteria. In particular, compounds 4d, 4h, and 4i showed the highest activity against S. aureus and Listeria monocytogenes, reaching remarkable MIC₁₀₀ values of 4 μg/mL and 8 μg/mL. The relationship between antimicrobial activity and compound structure has suggested that the presence of hydroxyl groups seems to be essential for antimicrobial activity of phenolic compounds.

High-quality conjugated polymers via one-pot Suzuki–Miyaura homopolymerization

Improving chemical integrity of polymers via one-pot Suzuki–Miyaura (SM) homopolymerization.

An Integrated Experimental/Theoretical Study of Structurally Related Poly-Thiophenes Used in Photovoltaic Systems

In this work, a series of eight thiophene-based polymers (exploited as “donors” in bulk heterojunction photovoltaics cells), whose structures were designed to be suitably tuned with the electronic characteristics of the [6,6]-Phenyl C61 butyric acid methyl ester (PCBM), is considered,. The electronic properties of the mono-, di-, trimeric oligomers are reckoned (at the Hartree-Fock and DFT level of the theory) and compared to experimental spectroscopic and electrochemical results. Indeed, electrochemical and spectroscopic results show a systematic difference whose physical nature is assessed and related to the exciton (electron-hole) binding energy (Je,h). The critical comparison of the experimental and theoretical band gaps, i.e., the HOMO-LUMO energy difference, suggests that electrochemical and DFT values are the most suited to being used in the design of a polythiophene-based p-n junction for photovoltaics.

On the hybrid glassy carbon electrode/OligoThiophene/Ag(NP) interface

GC/OligoThiophene/Ag(NP) hybrid interfaces are synthesized and characterized: GC is the glassy carbon surface; OligoThiophene stands for both an ultrathin bithiophene grafted film and a 4-Br-Bithiophene grafted polymer; Ag(NP) stands for silver nanoparticles. The hybrid interface preparation involves different steps: first, the electrode surface is functionalized through a combination of electrochemically assisted grafting (under reduction regime) and polymerization (under oxidation regime); then, silver nanoparticles are chemisorbed by dipping. In particular, an ultrathin film of grafted bithiophene can be obtained by applying one cyclic voltammetry reduction cycle (GC/BT surface), while subsequent cyclic voltammetry cycling under oxidation regime yields an immobilized 4Br-Bithiophene polymer (GC/4BrBT surface). AFM and TEM images were recorded to investigate the morphology and chemical composition of the Ag(NP). Fe(II)/Fe(III) cyclic voltammetry, Zn underpotential deposition (UPD), XPS, LA-ICP-MS, and Raman techniques were exploited to characterize both the GC/OligoThiophene and GC/OligoThiophene/Ag(NP) interfaces. Theoretical calculation, at the B3LYP/6-311G** level of the theory, enabled rationalization of the electroreduction mechanism and the Raman results.