Conjugated Polyelectrolyte (CPE) Poly{3-[6-(N-methylimidazolium)hexyl]-2,5-thiophene} Complexed with DNA: Relation between Colloidal Level Solution Structure and Chromic Effects

Main-Chain Cationic Polyelectrolytes: Design, Synthesis, and Applications

Polyelectrolytes have attracted a lot of attention spanning across disciplines, including polymer chemistry, materials chemistry, chemical biology, chemical engineering, as well as device physics, as a result of their widespread applications in sensing, biomedicine, food industry, wastewater treatment, optoelectronic devices, and renewable energy. In this review, we focus on the crucial synthetic strategies of structurally different classes of main-chain cationic polyelectrolytes. As a result of the presence of charged moieties in the main polymeric backbone, their solubility and photophysical properties can be easily tuned. Main-chain cationic polyelectrolytes provide various unique characteristics, including solubility in aqueous and organic solvents, easy processability, ease of film formation, ionic interaction, main-chain-directed charge transport, high conductivity, and aggregation. These properties make the main-chain polyelectrolyte a potential candidate for numerous applications ranging from chemo- and biosensing, antibacterial activity, optoelectronics, electrocatalysis, water splitting, ion conduction, to dye-sensitized solar cells.

Effect of solvents on intra- and inter-molecular interactions of oligothiophenes

CONTEXT

Oligothiophenes have long been used as model compounds to understand the chemistry of polythiophenes. Herein, we have some quantum chemical calculations and intra- and inter-molecular interaction calculations of a series of oligothiophenes such as terthiophene, quintetthiophene, sevensthiophene, terthiophene-terthiophene, terthiophene-water, terthiophene-methanol, and terthiophene-chloroform performed by time-dependent density functional theory (TD-DFT), density functional theory (DFT), and Multiwfn: a multifunctional wavefunction analyzer. The UV-vis spectra, HOMO-LUMO energies, NBO analysis, MEP, molecular structures, and electronic properties were computed using DFT/TD-DFT at the level of B3LYP/6-31+ G (d,p) and described. The nature of molecular interactions between terthiophene and solvents like water, methanol, and chloroform were also investigated using non-covalent interaction index (NCI), reduced density gradient (RDG), localized orbital locator (LOL), and electron localization function (ELF) topological analyses. Besides, Fukui functions and energy of population density-of-states were computed using the same method. The calculation results show that there are some changes in the terthiophene with the addition of solvent to the medium.

METHODS

DFT calculations were performed using the Gaussian 09 software and GaussView 5.0 visulation program. Multiwfn software is used to calculate the reduced density gradient (RDG) scatterplots, non-covalent interactions (NCI), ELF, LOL, Fukui analysis, and energy of population density-of-states of oligothiophenes.

Enhancement of charge-assisted hydrogen bond capabilities due to O-alkylation proximity in alkoxy cationic polythiophenes: solution- and solid-state evidence via EPR, AFM and surface free energy

Despite the array of applications for cationic polythiophenes (CPTs), there is still a need for structure-function guidelines and mechanistic understanding of their solution- and solid-state properties. This work presents a solution- and solid-state investigation of the effect of O-alkylation proximity on the hydrogen bonding (H-bonding) capabilities of alkoxy-CPTs, based on comparing an imidazolium alkoxy CPT with strong cation-pi, pi+ and positive charge-assisted hydrogen bonding (+CAHB) capabilities (PIMa), with two isothiouronium alkoxy CPTs with two-point +CAHB capabilities (PT1 & PT2), which have short and long alkoxy side chains, respectively. Our results show that a closer proximity of O-alkylation strengthens the +CAHB capabilities of PT1: in aqueous solutions, PT2 aggregates have a stronger interaction with cationic EPR spin probes than aggregates of PIMa and PT1, which in turn show a similar extent of repulsion towards the cationic spin probes. In solid-state, atomic force microscopy (AFM) shows that PIMa generates dendritic structures onto mica, with features of diffusion-limited aggregation (DLA), indicating strong interactions with the anionic substrate due to a high configurational entropy during spreading, regardless of being drop-casted from water or 1,4-dioxane-water (W-DI), despite the latter disturbing H-bonding due to selective solvation. PT1 is also capable of generating dendritic structures resembling ballistic aggregation (BA). However, this occurs only when casting from water, since W-DI generates island-like aggregates resembling attachment limited aggregation (ALA), which is the morphology generated by PT2 regardless of the solvent. Finally, spin-coated films of PIMa and PT1 show similar dispersivity of the surface free energy (SFE), which in turn is larger than that in PT2 films, which are also more affected when casted from W-DI, presenting much larger decreases of dispersivity. These results constitute a novel empirical structure-function guideline that could be useful for optimal design and/or processing of alkoxy CPTs. For example, dendritic patterns have recently gained attention since the colloidal droplet drying is related to engineering applications including inkjet printing, biosensing, and functional material design, while the SFE is relevant for opto- and bio-electronic applications of conjugated polyelectrolytes (CPEs). This information could also be useful when analyzing previous results obtained from alkoxy CPTs with different side chain lengths.

Cationic polythiophene-anionic fullerene pair in water and water-dioxane: studies on hydrogen bonding capabilities, kinetic and thermodynamic properties

Despite the vast array of solution- and solid-state bio-analytical, bioelectronic and optoelectronic applications of cationic polythiophenes (CPTs), the number of studies focused on the role of hydrogen bonding (H-bonding) between these and other molecules is scarce, regardless of whether H-bonding is expected to play an important role in several such applications. Also, despite the advantages of using cosolvents to systematically examine the molecular interactions, there are no such studies for CPTs to our knowledge. This work presents a steady-state UV-vis/fluorescence spectroscopic, kinetic and thermodynamic study on the H-bonding interactions between a water-soluble, cationic-anionic (isothiouronium-tetraphosphonate), polythiophene-fullerene donor-acceptor pair with two-point, charge-assisted H-bonding (CAHB) capabilities, tuned using water or a 1,4-dioxane-water mixture (W-DI). Both solvents generate photoinduced electron transfer (PET), fluorescence resonance energy transfer (FRET), spontaneous binding, H-bonding, ground-state complexing via multiple site binding, formation of micelle-like aggregates and equivalence points at a similar concentration of the quencher. However, in comparison with water, W-DI promotes less-ordered, less packed micellar aggregates, due to hydrophobic desolvation of the H-bond and larger solvent displacement during the PT1-4Fo complexation. This would decrease the extent of charge-transfer and the size of the sphere-of-quenching, mainly by displacements or rotations of the H-bonds, instead of elongations, together with a possible larger extent of diffusion-controlled static quenching. At [4Fo] larger than the equivalence point the micelles formed in water do not have available binding sites due to a tighter aggregation, causing a decrease in the quenching efficiency, while the micelles formed in W-DI start showing larger quenching efficiencies, possibly due to an increase in entropy that overcomes the desolvation of the H-bonding. These results could be useful when analyzing outputs from systems including CPTs with H-bonding capabilities, operating in (or casted from) solvents with clear differences in polarity and/or H-bonding capacity.

Structural and Photophysical Templating of Conjugated Polyelectrolytes with Single-Stranded DNA

A promising approach to influence and control the photophysical properties of conjugated polymers is directing their molecular conformation by templating. We explore here the templating effect of single-stranded DNA oligomers (ssDNAs) on cationic polythiophenes with the goal to uncover the intermolecular interactions that direct the polymer backbone conformation. We have comprehensively characterized the optical behavior and structure of the polythiophenes in conformationally distinct complexes depending on the sequence of nucleic bases and addressed the effect on the ultrafast excited-state relaxation. This, in combination with molecular dynamics simulations, allowed us a detailed atomistic-level understanding of the structure-property correlations. We find that electrostatic and other noncovalent interactions direct the assembly with the polymer, and we identify that optimal templating is achieved with (ideally 10-20) consecutive cytosine bases through numerous π-stacking interactions with the thiophene rings and side groups of the polymer, leading to a rigid assembly with ssDNA, with highly ordered chains and unique optical signatures. Our insights are an important step forward in an effective approach to structural templating and optoelectronic control of conjugated polymers and organic materials in general.

Effect of Spacer Length and Solvent on the Concentration-Driven Aggregation of Cationic Hydrogen-Bonding Donor Polythiophenes

Aggregation of cationic isothiouronium polythiophenes with alkoxy-spacers of different lengths at the 3-position of the thiophene ring was studied in solvents of different polarities. Hydrogen-bonding capacity was assessed by steady-state absorption and fluorescence spectroscopy, whereas the aggregation in aqueous solutions was studied by electron paramagnetic resonance spectroscopy, using paramagnetic probes of different polarities. The two polymers displayed similar features in respect to conformation, effect of cosolvents on aggregation, unstructured absorption-fluorescence spectra, Stokes shifts when aggregated, solvatochromic effect, and self-quenching concentration. However, these polymers also showed different specific interactions with water, Stokes shifts in water, effect of the solvent on the extent of dominant state of the S1 level, and also different inner cavities and hydrophobic-hydrophilic surface area in aqueous solution aggregates. Water maximized the difference between the polymers concerning the effect of specific increases in concentration, whereas the presence of 1,4-dioxane generated almost identical effects on both polymers.

Interactions of a zwitterionic thiophene-based conjugated polymer with surfactants

Structural organization and photoluminescence properties of zwitterionic conjugated polymer–surfactant assemblies depend on specific and non-specific polymer–surfactant interactions within the aggregate.