Vesicles, fibres, films and crystals: A low-molecular-weight-gelator [Au(6-thioguanosine)2]Cl which exhibits a co-operative anion-induced transition from vesicles to a fibrous metallo-hydrogel.

We describe a simple coordination compound of Au(I) and 6-thioguanosine, [Au(6-tGH)2]Cl, that has a rich self-assembly chemistry. In aqueous solution, the discrete complex assembles into a supramolecular fibre and forms a luminescent hydrogel at concentrations above about 1 mM. Below this concentration, the macromolecular structure is a vesicle. Through appropriate control of the solvent polarity, the gel can be turned into a lamellar film or crystallised. The molecular structure of [Au(6-tGH)2]Cl was determined using single crystal X-ray diffraction, which showed bis-6-thioguanosine linearly coordinated through the thione moiety to a central Au(I) ion. In the vesicles, the photoluminescence spectrum shows a broad, weak band at 550 nm owing to aurophilic interactions. Co-operative self-assembly from vesicle to fibre is made possible through halogen hydrogen bonding interactions and the aurophilic interactions are lost, resulting in a strong photoluminescence band at 490 nm with vibronic structure typical of an intraligand transition. The vesicle-fibre transition is also revealed by a large increase of ellipticity in the circular dichroism spectrum with a prominent peak near 390 nm owing to the helical structure of the fibres. Atomic force microscopy shows that at the same time as fibres form, the sample gels. Imaging near the vesicle-fibre transition shows that the fibres form between vesicles and a mechanism for the transition based on vesicle collisions is proposed.

Models for sensing by nanowire networks: application to organic vapour detection by multiwall carbon nanotube-DNA films.

Electronic sensors for volatile organic compounds have been prepared by drop-casting dispersions of multi-wall carbon nanotubes (MWCNTs) in aqueous solutions ofλ-DNA onto Pt microband electrodes. The MWCNTs themselves show a metal-like temperature dependence of the conductance, but the conductance of DNA/MWCNT composites has an activated component that corresponds to inter-tube tunneling. The resistance of the composite was modelled by a series combination of a term linear in temperature for the nanotubes and a stretched exponential form for the inter-tube junctions. The resistance may increase or decrease with temperature according to the composition and may be tuned to be almost temperature-independent at 67% by mass of DNA. Upon exposure to organic vapours, the resistance of the composites increases and the time-dependence of this signal is consistent with diffusion of the vapour into the composite. The fractional change in resistance at steady-state provides an analytical signal with a linear calibration and the presence of DNA enhances the signal and adjusts the selectivity in favour of polar analytes. The temperature dependence of the signal is determined by the enthalpy of adsorption of the analyte in the inter-tube junctions and may be satisfactorily modelled using the Langmuir isotherm. Temperature and pressure-dependent studies indicate that neither charge injection by oxidation/reduction of the analyte nor condensation of analyte on the device is responsible for the signal. We suggest that the origin of the sensing response is an adsorption of the analyte in the inter-tube regions that modulates the tunneling barriers. This suggests a general route to tuning the selectivity of MWCNT gas sensors using non-conductive polymers of varying chemical functionality.

transoid and cisoid Conformations in Silver-Mediated Cytosine Base Pairs: Hydrogen Bonding Dictates Argentophilic Interactions in the Solid State.

We have synthesized and structurally characterized examples of the well-known silver-mediated DNA base pair in its simplest possible form, as [AgI-bis-(N3-cytosine)]+. The compounds show differences such as variable coordination geometry, conformation with cisoid and transoid arrangements, and, in one case, intramolecular base pairing. Collectively, these compounds represent three of five permutations of linear/bent coordination geometry and cisoid/transoid arrangement of the cytosine ligands and contain the global minimum conformation as determined by DFT calculations: bent-transoid. Furthermore, these compounds show no argentophilic intercomplex interactions in the solid state, in marked contrast to alkylated and nucleoside analogues, and so do not form the supramolecular 1D "metallo-DNA" duplex observed in those cases but instead form hydrogen-bonded sheets. This marked difference may be attributed, in part, to the additional hydrogen bond donor site at N1 of the nucleobase that ubiquitously participates in intermolecular interactions.

Enhancing the kinetics of hydrazone exchange processes: an experimental and computational study.

The capacity of hydrazone bonds to readily undergo component exchange processes sees their extensive utilization in dynamic combinatorial chemistry. The kinetics of hydrazone exchange are optimal at pH ∼4.5, which limits the use of hydrazone-based dynamic combinatorial libraries, particularly for biological targets which are only stable at near-neutral pH values. It would thus be advantageous if hydrazone exchange proceeded with faster rates at pH values closer to neutral. We experimentally and computationally evaluated the hypothesis that hydrazones possessing neighbouring acidic or basic functional groups within the carbonyl-derived moitety of the hydrazone would enhance exchange rates. Our work suggests that judiciously placed N- or O-hydrogen bond acceptors within the carbonyl-derived moiety of the hydrazone stabilize transition states via hydrogen bonding interactions, providing a valuable boost to exchange kinetics at near-neutral pH values. We anticipate these findings will be of interest in dynamic combinatorial chemistry, dynamic covalent polymers/materials, functionalized nanoparticles and interlocked molecules, all of which may benefit from hydrazone exchange processes able to operate at near-neutral pH values.

Nanoscale silicon substrate patterns from self-assembly of cylinder forming poly(styrene)-block-poly(dimethylsiloxane) block copolymer on silane functionalized surfaces.

Poly(styrene)-block-poly(dimethylsiloxane) (PS-b-PDMS) is an excellent block copolymer (BCP) system for self-assembly and inorganic template fabrication because of its high Flory-Huggins parameter (χ âˆ¼ 0.26) at room temperature in comparison to other BCPs, and high selective etch contrast between PS and PDMS block for nanopatterning. In this work, self-assembly in PS-b-PDMS BCP is achieved by combining hydroxyl-terminated poly(dimethylsiloxane) (PDMS-OH) brush surfaces with solvent vapor annealing. As an alternative to standard brush chemistry, we report a simple method based on the use of surfaces functionalized with silane-based self-assembled monolayers (SAMs). A solution-based approach to SAM formation was adopted in this investigation. The influence of the SAM-modified surfaces upon BCP films was compared with polymer brush-based surfaces. The cylinder forming PS-b-PDMS BCP and PDMS-OH polymer brush were synthesized by sequential living anionic polymerization. It was observed that silane SAMs provided the appropriate surface chemistry which, when combined with solvent annealing, led to microphase segregation in the BCP. It was also demonstrated that orientation of the PDMS cylinders may be controlled by judicious choice of the appropriate silane. The PDMS patterns were successfully used as an on-chip etch mask to transfer the BCP pattern to underlying silicon substrate with sub-25 nm silicon nanoscale features. This alternative SAM/BCP approach to nanopattern formation shows promising results, pertinent in the field of nanotechnology, and with much potential for application, such as in the fabrication of nanoimprint lithography stamps, nanofluidic devices or in narrow and multilevel interconnected lines.

Marine antifouling performance of polymer coatings incorporating zwitterions.

Zwitterionic materials display antifouling promise, but their potential in marine anti-biofouling is still largely unexplored. This study evaluates the effectiveness of incorporating small quantities (0-20% on a molar basis) of zwitterions as sulfobetaine methacrylate (SBMA) or carboxybetaine methacrylate (CBMA) into lauryl methacrylate-based coatings whose relatively hydrophobic nature encourages adhesion of the diatom Navicula incerta, a common microfouling organism responsible for the formation of 'slime'. This approach allows potential enhancements in antifouling afforded by zwitterion incorporation to be easily quantified. The results suggest that the incorporation of CBMA does provide a relatively minor enhancement in fouling-release performance, in contrast to SBMA which does not display any enhancement. Studies with coatings incorporating mixtures of varying ratios of the cationic monomer [2-(methacryloyloxy)ethyl]trimethylammonium chloride and the anionic monomer (3-sulfopropyl)methacrylate, which offer a potentially lower cost approach to the incorporation of anionic and cationic charge, suggest these monomers impart little significant effect on biofouling.

Metal-conductive polymer hybrid nanostructures: preparation and electrical properties of palladium-polyimidazole nanowires.

A simple, convenient method for the formation of hybrid metal/conductive polymer nanostructures is described. Polyimidazole (PIm) has been templated on λ-DNA via oxidative polymerisation of imidazole using FeCl3 to produce conductive PIm/DNA nanowires. The PIm/DNA nanowires were decorated with Pd (Pd/PIm/DNA) by electroless reduction of PdCl4(-2) with NaBH4 in the presence of PIm/DNA; the choice of imidazole was motivated by the potential Pd(II) binding site at the pyridinic N atom. The formation of PIm/DNA and the presence of metallic Pd on Pd/PIm/DNA nanowires were verified by FTIR, UV-vis and XPS spectroscopy techniques. AFM studies show that the nanowires have diameters in the range 5-45 nm with a slightly greater mean diameter (17.1 ± 0.75 nm) for the Pd-decorated nanowires than the PIm/DNA nanowires (14.5 ± 0.89 nm). After incubation for 24 h in the polymerisation solution, the PIm/DNA nanowires show a smooth, uniform morphology, which is retained after decoration with Pd. Using a combination of scanned conductance microscopy, conductive AFM and two-terminal measurements we show that both types of nanowire are conductive and that it is possible to discriminate different possible mechanisms of transport. The conductivity of the Pd/PIm/DNA nanowires, (0.1-1.4 S cm(-1)), is comparable to the PIm/DNA nanowires (0.37 ± 0.029 S cm(-1)). In addition, the conductance of Pd/PIm/DNA nanowires exhibits Arrhenius behaviour (E(a )= 0.43 ± 0.02 eV) as a function of temperature in contrast to simple Pd/DNA nanowires. These results indicate that although the Pd crystallites on Pd/PIm/DNA nanowires decorate the PIm polymer, the major current pathway is through the polymer rather than the Pd.

Metal-enhanced luminescence of silicon quantum dots: effects of nanoparticles and molecular electron donors and acceptors on the photofading kinetics.

Alkyl-capped silicon quantum dots (SiQDs) show enhanced luminescence when drop cast as films on glass slides in mixtures with Ag or Au nanoparticles or the electron donor ferrocene (Fc). Metal enhancement of quantum dot photoluminescence (PL) is known to arise from a combination of the intense near-field associated with the surface plasmon of the metal on the rate of absorption and the decrease in the lifetime of the excited state. Here we present evidence that an additional factor is also involved: electron transfer from the metal to the quantum dot. Under CW irradiation with an argon ion laser at 488 nm, SiQDs undergo a reversible photofading of the PL as the particles photoionize. A steady-state condition is established by the competition between photoionization and electron-hole recombination. The fading of the initial PL I0 to the steady-state value I∞ can be modelled by a simple first order decay with a lognormal distribution of rates, which reflects the heterogeneity of the sample. In the presence of Ag and Au nanoparticles, the modal rate constants of photofading increase by factors of up to 4-fold and the ratio I0/I∞ decreases by factors up to 5-fold; this is consistent with an increase in the rate of electron-hole recombination facilitated by the metal nanoparticles acting as sources of electrons. Further support for this interpretation comes from the enhancement in PL observed in photofading experiments with films of SiQDs mixed with Fc; this compound is a well-known one-electron donor, but shows no plasmon band which complicates the estimation of PL enhancement with Ag NPs.

Stealth Amphotericin B nanoparticles for oral drug delivery: In vitro optimization.

PURPOSE: Amphotericin B (AmB) is an effective anti-fungal and anti-leishmanial agent. However, AmB has low oral bioavailability (0.3%) and adverse effects (e.g., nephrotoxicity). The objectives of this study were to improve the oral bioavailability by entrapping AmB in pegylated (PEG) poly lactide co glycolide copolymer (PLGA-PEG) nanoparticles (NPs). The feasibility of different surfactants and stabilizers on the mean particle size (MPS) and entrapment efficiency were also investigated. MATERIALS AND METHODS: NPs of AmB were prepared by a modified emulsification diffusion method employing a vitamin E derivative as a stabilizer. Physicochemical properties and particle size characterization were evaluated using Fourier Transform Infra-Red spectroscopy (FTIR), differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. Moreover, in vitro dissolution profiles were performed for all formulated AmB NPs. RESULTS: MPS of the prepared spherical particles of AmB ranged from 26.4 ± 2.9 to 1068 ± 489.8 nm. An increased stirring rate favored AmB NPs with a smaller MPS. There was a significant reduction in MPS, drug content and drug release, when AmB NPs were prepared using the diblock polymer PLGA-PEG with 15% PEG. Addition of three emulsifying agents poly vinyl pyrrolidone (PVP), Vitamin E (TPGS) and pluronic F-68 to AmB formulations led to a significant reduction in particle size and increase in drug entrapment efficiency (DEE) compared to addition of PVP alone. FTIR spectroscopy demonstrated a successful loading of AmB to pegylated PLGA-PEG copolymers. PLGA-PEG copolymer entrapment efficiency of AmB was increased up to 56.7%, with 92.7% drug yield. After a slow initial release, between 20% and 54% of AmB was released in vitro within 24 h phosphate buffer containing 2% sodium deoxycholate and were best fit Korsmeyer-Peppas model. In conclusion, PLGA-PEG diblock copolymer with 15% PEG produced a significant reduction (>70%) in MPS with highest drug content. The percentage of PEG in the copolymer and the surfactant/stabilizer used had a direct effect on AmB release in vitro, entrapment efficiency and MPS. These developed formulations are feasible, effective and improved alternatives to other carriers for oral delivery of AmB.

Mechanism of formation of supramolecular DNA-templated polymer nanowires.

Details of the mechanism of formation of supramolecular polymer nanowires by templating on DNA are revealed for the first time using AFM. Overall these data reveal that the smooth, regular, structures produced are rendered by highly dynamic supramolecular transformations occurring over the micrometre scale. In the initial stages of the process a low density of conducting polymer (CP) binds to the DNA as, essentially, spherical particles. Further reaction time produces DNA strands which are more densely packed with particles giving a beads-on-a-string appearance. The particles subsequently undergo dynamic reconfiguration so as to elongate along the template axis and merge to yield the highly regular, smooth morphology of the final nanowire. MD simulations illustrate the early stages of the process showing the binding of globular CP to duplex DNA, while the latter stages can be modeled effectively by a linear thermodynamic description based on the balance between the line energy, which accounts for adhesion of the material to the template, and its surface tension. This model accounts for the phenomena observed in the AFM studies: the relative success of DNA templating of polymers compared to metals; the slow approach to equilibrium; and the observed thinning and 'necking' phenomena as the structures transform from beads-on-a-string to smooth nanowire.

Real-time activity bioassay of single osteoclasts using a silicon nanocrystal-impregnated artificial matrix.

The lack of an in vitro real-time osteoclast (OC) activity assay has hampered mechanistic studies of bone resorption. Such an assay is developed, employing a hydroxyapatite matrix impregnated with alkyl-capped silicon nanocrystals, which is capable of monitoring the time-course of resorption by single osteoclasts. Resorption of the matrix by OC releases the nanocrystals, which are internalized by the cell and detected as an increase in OC luminescence. This particular choice of nanocrystals is motivated by their bright pH-independent luminescence, proportional to concentration, and by their rapid uptake without cytotoxicity. In this in vitro assay, OCs are inhibited by calcitonin (CT) and methyl-ß-cyclodextrin (MCD), and stimulated by receptor activator of nuclear factor kappa-B ligand (RANKL) in the expected manner. The kinetics of the assay exhibit a lag phase representing cell attachment and commencement of resorption processes, followed by a growth of cell luminescence intensity, and the whole time-course is satisfactorily described by the logistic equation.

Conductive, monodisperse polyaniline nanofibers of controlled length using well-defined cylindrical block copolymer micelles as templates.

Stable colloidal dispersions of polyaniline (PAni) nanofibers with controlled lengths from about 200 nm-1.1 µm and narrow length distributions (Lw/Ln < 1.04; Lw = weight average micelle length, Ln = number average micelle length) were prepared through the template-directed synthesis of PAni using monodisperse, solution-self-assembled, cylindrical, block copolymer micelles as nanoscale templates. These micelles were prepared through a crystallization-driven living self-assembly method from a poly(ferrocenyldimethylsilane)-b-poly(2-vinylpyridine) block copolymer (PFS25 -b-P2VP425). This material was initially self-assembled in iPrOH to form cylindrical micelles with a crystalline PFS core and a P2VP corona and lengths of up to several micrometers. Sonication of this sample then yielded short cylinders with average lengths of 90 nm and a broad length distribution (Lw/Ln = 1.32). Cylindrical micelles of PFS25 -b-P2VP425 with controlled lengths and narrow length distributions (Lw/Ln < 1.04) were subsequently prepared using thermal treatment at specific temperatures between 83.5 and 92.0 °C using a 1D self-seeding process. These samples were then employed in the template-directed synthesis of PAni nanofibers through a two-step procedure, where the micellar template was initially stabilised by deposition of an oligoaniline coating followed by addition of a polymeric acid dopant, resulting in PAni nanofibers in the emeraldine salt (ES) state. The ES-PAni nanofibers were shown to be conductive by scanning conductance microscopy, whereas the precursor PFS25-b-P2VP425 micelle templates were found to be dielectric in character.

Hierarchical self-assembly in an RNA-based coordination polymer hydrogel.

An RNA-based coordination polymer is formed by the aqueous reaction of CuI ions with the thionucleoside enantiomer (-)6-thioguanosine, (6tGH). The resulting polymer, [CuI(µ3-S-thioG)]n1, has a one-dimensional structure based on a [Cu4-S4] core and undergoes extensive hierarchical self-assembly transforming from oligomeric chains → rod → cable → bundle through which a fibrous gel forms, that undergoes syneresis to form a self-supporting mass. The assembly involves the formation of helical cables/bundles and, in combination with the intrinsic photoemission of the polymer, results in the material exhibiting circularly polarised luminescence (CPL).

Computational analysis and experimental verification of donor-acceptor behaviour of berberine, and its co-oligomers and co-polymers with ethylenedioxythiophene.

The donor-acceptor (D-A) type of conjugated polymers has emerged as the paradigm of the third generation of electronically conducting polymers demonstrating improved infrared activity and intrinsic electronic conductivity. Judicious selection of donor (D) and acceptor (A) monomers for copolymerization can further fine-tune these properties. Notably, for such refinement, natural compounds provide many conjugated molecules with various functional groups. Berberine cation (Ber+) found in Coscinium fenestratum has extensive conjugation and contains both an electron deficient isoquinolium A moiety and electron-rich D-type methylenedioxy and methoxy groups. The incorporation of natural products in electronic materials is a novel area of research which opens a wide scope for future electronic and optoelectronic devices. Investigation of their fundamental properties via computer simulations is therefore important. In this study, quantum chemical calculations are performed using density functional theory (DFT) to investigate the electronic and optical properties of oligomers of Ber+ and 3,4-ethylenedioxythiophene (EDOT) and to explore the possibilities for homo-polymerization of Ber+ and its copolymerization with EDOT. It has been revealed that homo-polymerization is not favoured but copolymerization with EDOT is possible. As such, Ber+ was copolymerized with EDOT and the copolymers formed by electro-polymerization are extensively characterised and the D-A behaviour of the copolymers verified. Furthermore, the theoretical predictions have been compared with the experimental data.

Berberine isolation from Coscinium fenestratum: optical, electrochemical, and computational studies.

Berberine was extracted from Coscinium fenestratum (tree turmeric) and purified by column chromatography. The UV-Vis absorption spectroscopy of berberine was studied in acetonitrile and aqueous media. TD-DFT calculations employing the B3LYP functional were found to reproduce the general features of the absorption and emission spectra correctly. The electronic transitions to the first and second excited singlet states involve a transfer of electron density from the electron donating methylenedioxy phenyl ring to the electron accepting isoquinolium moiety. An estimate of the electrochemical gap (2.64 V) was obtained from microelectrode voltammetry and good agreement was found with quantum chemical calculations using the cc-pVTZ basis set and the B3LYP, CAM-B3LYP and wB97XD functionals. The calculations indicate spin density of the radical dication is delocalised over the molecule. These basic data are useful for assessment of the synthesis of donor-acceptor polymeric materials employing oxidative polymerization or co-polymerisation of berberine.

Synthesis, characterisation and electrical properties of supramolecular DNA-templated polymer nanowires of 2,5-(bis-2-thienyl)-pyrrole.

Supramolecular polymer nanowires have been prepared by using DNA-templating of 2,5-(bis-2-thienyl)-pyrrole (TPT) by oxidation with FeCl(3) in a mixed aqueous/organic solvent system. Despite the reduced capacity for strong hydrogen bonding in polyTPT compared to other systems, such as polypyrrole, the templating proceeds well. FTIR spectroscopic studies confirm that the resulting material is not a simple mixture and that the two types of polymer interact. This is indicated by shifts in bands associated with both the phosphodiester backbone and the nucleobases. XPS studies further confirm the presence of DNA and TPT, as well as dopant Cl(-) ions. Molecular dynamics simulations on a [{dA(24):dT(24)}/{TPT}(4)] model support these findings and indicate a non-coplanar conformation for oligoTPT over much of the trajectory. AFM studies show that the resulting nanowires typically lie in the 7-8 nm diameter range and exhibit a smooth, continuous, morphology. Studies on the electrical properties of the prepared nanowires by using a combination of scanned conductance microscopy, conductive AFM and variable temperature two-terminal I-V measurements show, that in contrast to similar DNA/polymer systems, the conductivity is markedly reduced compared to bulk material. The temperature dependence of the conductivity shows a simple Arrhenius behaviour consistent with the hopping models developed for redox polymers.

Equilibrium and non-equilibrium thermodynamics of templating reactions for the formation of nanowires.

The thermodynamics of the templating of materials on one-dimensional templates, such as DNA, is modeled by considering two terms: the surface tension of the material (γ) and a line energy (σ = 2πr(T)γ(T)) that represents the adhesion of the material to the template (radius r(T)). We show that as long as the reaction stoichiometry does not exceed a certain limit (√[3ν/2π] < r(T) [absolute value]γ(T)[absolute value]/γ ; ν = volume of material per unit length of template) then a sample of smooth, uniform wires is the equilibrium state. If the amount of material exceeds this limit, then the material will comprise a single macroscopic particle at equilibrium. The behavior of the system is similar to a morphological wetting transition and the model can rationalize the available experimental data on the reaction conditions required to form smooth DNA-templated nanowires. Using the framework of linear non-equilibrium thermodynamics, we also show that the model can describe qualitatively the observed evolution of these nanostructures from beads-on-a-string morphologies to smooth nanowires and construct a stochastic differential equation for the process. Numerical simulations and scaling arguments suggest that the same scaling behavior as the Edwards-Wilkinson equation is observed.

Smooth and conductive DNA-templated Cu2O nanowires: growth morphology, spectroscopic and electrical characterization.

DNA strands have been used as templates for the self-assembly of smooth and conductive cuprous oxide (Cu2O) nanowires of diameter 12-23 nm and whose length is determined by the template (16 µm for λ-DNA). A combination of spectroscopic, diffraction and probe microscopy techniques showed that these nanowires comprise single crystallites of Cu2O bound to the DNA molecules which fused together over time in a process analogous to Ostwald ripening, but driven by the free energy of interaction with the template as well as the surface tension. Electrical characterization of the nanowires by a non-contact method, scanned conductance microscopy and by contact mode conductive AFM showed the wires are electrically conductive. The conductivity estimated from the AFM cross section and the zero-bias conductance in conductive AFM experiments was 2.2-3.3 S cm⁻¹. These Cu2O nanowires are amongst the thinnest reported and show evidence of strong quantum confinement in electronic spectra.

Circularly polarised luminescence in an RNA-based homochiral, self-repairing, coordination polymer hydrogel.

The aqueous equimolar reaction of Ag(i) ions with the thionucleoside enantiomer (-)6-thioguanosine, ((-)6tGH), yields a one-dimensional coordination polymer {Ag(-)tG} n , the self-assembly of which generates left-handed helical chains. The resulting helicity induces an enhanced chiro-optical response compared to the parent ligand. DFT calculations indicate that this enhancement is due to delocalisation of the excited state along the helical chains, with 7 units being required to converge the calculated CD spectra. At concentrations ≥15 mmol l-1 reactions form a sample-spanning hydrogel which shows self-repair capabilities with instantaneous recovery in which the dynamic reversibility of the coordination chains appears to play a role. The resulting gel exhibits circularly polarised luminescence (CPL) with a large dissymmetry factor of -0.07 ± 0.01 at 735 nm, a phenomenon not previously observed for this class of coordination polymer.

Implementing the donor-acceptor approach in electronically conducting copolymers via electropolymerization.

Electropolymerization has become a convenient method for synthesizing and characterizing complex organic copolymers having intrinsic electronic conductivity, including the donor (D)-acceptor (A) class of electronically conducting polymers (ECPs). This review begins with an introduction to the electrosynthesis of common second-generation ECPs. The information obtainable from electroanalytical studies, charge carriers such as polarons (positive and negative) and bipolarons (positive and negative) and doping will be discussed. The evolutionary chain of ECPs is then presented. ECPs comprising electron-rich D and electron-deficient A moieties have been shown to possess intrinsic electronic conductivity and unique optical and electronic properties. They are third generation ECPs and electropolymerization of mixtures of D and A leads to stoichiometrically controlled block copolymers. These D-A type ECPs are discussed on the basis of selected representative materials. Since the discovery of electropolymerization as a powerful tool to synthesize copolymers of conjugated monomers with a pre-determined ratio of D and A repeat units present in the polymer, the field of D-A type ECPs has grown considerably and the literature available since 2004 to 2021 is summarized and tabulated. Electronic and optical properties of the materials determined by computational chemistry are presented. The data obtained from electrochemical and optical methods are compared with those obtained from computational methods and reasons for discrepancies are given. The literature on the concept of electropolymerization extended to synthesizing triblock and many-block copolymers is reviewed. Finally, applications of D-A polymers in optoelectronic devices (organic solar cells and field-effect transistors) and in bio-imaging are explained quoting appropriate examples.