α,ω-Dithiol Oligo(phenylene vinylene)s for the Preparation of High-Quality π-Conjugated Self-Assembled Monolayers and Nanoparticle-Functionalized Electrodes

While thioacetate-terminated oligo(phenylene vinylene)s (OPVs) have been synthesized and employed in applications involving the formation of metal–molecule–metal junctions, the synthesis and application of potentially more versatile α,ω-dithiol OPVs have not previously been described. Here, a thiomethyl-precursor route to the synthesis of α,ω-dithiol OPVs is reported and their ability to form well-ordered self-assembled monolayers (SAMs) without the addition of exogenous deprotection reagents is described. α,ω-Dithiol OPV monolayers exhibit thicknesses consistent with molecular length and are nearly defect-free, as assayed by electrochemical measurements. To demonstrate the ease with which SAMs containing these bifunctional OPVs can, in contrast to thioacetate functionalized OPVs, be further functionalized with materials other than gold, we have modified them in a single step with a sub-monolayer of cadmium selenide nanocrystals (NCs). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) confirm that these NC-modified films are both smooth and uniform over the largest areas investigated (\u3e 10 μm2) and no evidence of NC aggregation is observed. To evaluate the electrochemical response of these metal–molecule– semiconductor assemblies we have fabricated NC-modified OPV SAMs with ferrocene-coated NCs. Variable-frequency alternating current voltammetry indicates that electron transfer in these assemblies is much more rapid than in analogous structures formed using simple alkane dithiols. It thus appears that α,ω-dithiol OPVs are well suited for the formation of high-quality conducting SAMs for the functionalization of gold and other surfaces

Improved prediction of the optical properties in pi-conjugated polymers: the case of benzochalcogenodiazole-based copolymers with different heteroatom substitution

Donor−acceptor (D−A) approach to conjugated polymer design has become a widely used method for preparing conjugated polymers with narrow band gaps.1 One outstanding D−A polymer is poly(cyclopentadithiophene)benzothiadiazole, PCPDTBT (P1 in Figure 1), for which power conversion efficiencies in solar cells of 4.5-5.5% are reported.2 In this work, we use resonance Raman (RR) and density functional theory (DFT) calculations to investigate the tuning of the electronic and structural properties of cyclopentadithiophene-benzochalcogenodiazole D−A polymers, wherein a single atom in the benzochalcogenodiazole unit is varied from sulfur to selenium to tellurium (Fig. 1).3 Sophisticated DFT calculations have been carried out using long-range corrected functionals, considering both tuned and default range-separation parameters, aiming at predicting their optical and charge transport properties. In addition, the nature of the electronic excitation is described by analyzing the enhancement pattern in the RR spectra using Raman excitation wavelengths coincident with the various transitions in the copolymers.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

α,ω-Dithiol Oligo(phenylene vinylene)s for the Preparation of High-Quality π-Conjugated Self-Assembled Monolayers and Nanoparticle-Functionalized Electrodes

While thioacetate-terminated oligo(phenylene vinylene)s (OPVs) have been synthesized and employed in applications involving the formation of metal–molecule–metal junctions, the synthesis and application of potentially more versatile α,ω-dithiol OPVs have not previously been described. Here, a thiomethyl-precursor route to the synthesis of α,ω-dithiol OPVs is reported and their ability to form well-ordered self-assembled monolayers (SAMs) without the addition of exogenous deprotection reagents is described. α,ω-Dithiol OPV monolayers exhibit thicknesses consistent with molecular length and are nearly defect-free, as assayed by electrochemical measurements. To demonstrate the ease with which SAMs containing these bifunctional OPVs can, in contrast to thioacetate functionalized OPVs, be further functionalized with materials other than gold, we have modified them in a single step with a sub-monolayer of cadmium selenide nanocrystals (NCs). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) confirm that these NC-modified films are both smooth and uniform over the largest areas investigated (\u3e 10 μm2) and no evidence of NC aggregation is observed. To evaluate the electrochemical response of these metal–molecule– semiconductor assemblies we have fabricated NC-modified OPV SAMs with ferrocene-coated NCs. Variable-frequency alternating current voltammetry indicates that electron transfer in these assemblies is much more rapid than in analogous structures formed using simple alkane dithiols. It thus appears that α,ω-dithiol OPVs are well suited for the formation of high-quality conducting SAMs for the functionalization of gold and other surfaces

Robust Visible Light Photoswitching with Ortho-Thiol Substituted Azobenzenes

Introduction of S-ethyl groups in all four ortho positions of azobenzene prevents reduction of the azo group by intracellular glutathione, while enhancing the absorptivity to ∼10000 M−1 cm−1 in the blue and green regions of the visible spectrum. cis-to-trans isomerization occurs thermally on the minutes timescale. Further, this substitution pattern permits switching with red light, a color that is more penetrating through biological tissues than other parts of the visible spectrum

A Mechanistic Study of Halogen Addition and Photoelimination from ?-Conjugated Tellurophenes

The ability to drive reactivity using visible light is of importance for many disciplines of chemistry and has significant implications for sustainable chemistry. Identifying photochemically active compounds and understanding photochemical mechanisms is important for the development of useful materials for synthesis and catalysis. Here we report a series of photoactive diphenyltellurophene compounds bearing electron-withdrawing and electron-donating substituents synthesized by alkyne coupling/ring closing or palladium-catalyzed ipso-arylation chemistry. The redox chemistry of these compounds was studied with respect to oxidative addition and photoelimination of bromine, which is of importance for energy storage reactions involving X₂. The oxidative addition reaction mechanism was studied using density functional theory, the results of which support a three-step mechanism involving the formation of an initial η¹ association complex, a monobrominated intermediate, and finally the dibrominated product. All of the tellurophene derivatives undergo photoreduction using 430, 447, or 617 nm light depending on the absorption properties of the compound. Compounds bearing electron-withdrawing substituents have the highest photochemical quantum efficiencies in the presence of an alkene trap, with efficiencies of up to 42.4% for a pentafluorophenyl-functionalized tellurophene. The photoelimination reaction was studied in detail through bromine trapping experiments and laser flash photolysis, and a mechanism is proposed. The photoreaction, which occurs by release of bromine radicals, is competitive with intersystem crossing to the triplet state of the brominated species, as evidenced by the formation of singlet oxygen. These findings should be useful for the design of new photochemically active compounds supported by main-group elements

Modelling the optical properties of Benzochalcogenodiazole-based Copolymers using Tuned Range-Separated Hybrid Functionals

Since the discovery of organic semiconductors, these systems have been deeply investigated and many strategies to module their optical and electronic properties have been established. In this sense, Donor-acceptor (D−A) approach to conjugated polymer design has become a widely used method for preparing conjugated polymers with narrow band gaps. This approach involves synthesizing a polymer with a delocalized π-electron system that comprises alternating electron-rich (donor) and electron-deficient (acceptor) repeat units. The combination of high-lying HOMO levels (residing on the donor units) and low-lying LUMO levels (residing on the acceptor units) results in an overall narrow band gap for the polymer. In this sense, poly(cyclopentadithiophene)benzothiadiazole is a D−A polymer for which power conversion efficiencies in solar cells of 5 6 % are reported. In this work, we use density functional theory (DFT) calculations to investigate the tuning of the electronic and structural properties of cyclopentadithiophene ben zochalcogenodiazole D−A polymers, wherein a single atom in the benzochalcogenodiazole unit is varied from sulfur to selenium to tellurium. Resonance Raman (RR) spectroscopy is also used to describe the nature of the electronic excitations. Improved prediction of the optical properties h as been obtained by using long range corrected functionals functionals, considering both tuned and default range separation parameters, aiming at predicting their optical and charge transport properties.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

The Challenge of Synthesizing Oligomers for Molecular Wires

Controlling the size of the oligomer and introducing functional groups at the ends of the oligomer that allow it to react with separate electrodes are critical issues when preparing materials for molecular wires. We demonstrate a general synthetic approach to oligophenylenevinylene (OPV) derivative molecules with a molecular length up to 9–10 nm which allow for the introduction of aromatic thioacetate functionality in fully conjugated oligomer systems. Oligomers containing 3–15 phenyl units were synthesized by step wise Horner-Wadsworth-Emmons (HWE) reactions of a bifunctional OPV-monomer, which demonstrated good control of the size of the OPVs. Workup after each reaction step ensures a high purity of the final products. End group functionalization was introduced as a last step

Nanostructured luminescently labeled nucleic acids

Important and emerging trends at the interface of luminescence, nucleic acids and nanotechnology are: (i) the conventional luminescence labeling of nucleic acid nanostructures (e.g. DNA tetrahedron); (ii) the labeling of bulk nucleic acids (e.g. single‐stranded DNA, double‐stranded DNA) with nanostructured luminescent labels (e.g. copper nanoclusters); and (iii) the labeling of nucleic acid nanostructures (e.g. origami DNA) with nanostructured luminescent labels (e.g. silver nanoclusters). This review surveys recent advances in these three different approaches to the generation of nanostructured luminescently labeled nucleic acids, and includes both direct and indirect labeling methods