A Review on Self-Assembly Driven Optoelectronic Properties of Polythiophene-Peptide and Polythiophene-Polymer Conjugates.

Polythiophene (PT) is an important conducting polymer for its outstanding optoelectronic properties. Here, we delineate the self-assembly-driven optoelectronic properties of PT-peptide and PT-polymer conjugates, taking examples from recent literature reports. PT-peptide conjugates made by both covalent and noncovalent approaches are discussed. Poly(3-thiophene acetic acid) (P3TAA) covalently coupled with Gly-Gly-His tripeptide, C-protected and deprotected tripeptide H2N-F-F-V-OMe, etc. exhibits self-assembly-driven absorbance, fluorescence, photocurrent, and electronic properties. Noncovalent PT-peptide conjugates produced via ionic, H-bonding, and π-stacking interactions show tunable morphology and optoelectronic properties by varying the composition of a component. PT conjugated with Alzheimer's disease peptide (KLVFFAE, Aß16-22) shows enhanced photocatalytic water splitting, cationic PT(CPT-I)-perylene bisimide-appended dipeptide (PBI-DY), and anionic PT-perylene diimide-appended cationic peptide (PBI-NH3+) conjugates and exhibits self-assembly-driven enhanced photoswitching and organic mixed electronic and ionic conductivity (OMEIC) properties. In the PT-polymer conjugates, self-assembly-driven optoelectronic properties of covalently produced PT-random copolymers, PT-block copolymers, PT-graft-random copolymers, and PT-graft-block copolymer conjugates are discussed. The HOMO-LUMO levels of hyperbranched polymers are optimized to obtain better power conversion efficiency (PCE) in the bulk heterojunction (BHJ) solar cell than in linear polymers, and P3TAA-ran-P3HT (43 mol % P3TAA) conjugated with MAPbI3 perovskite exhibits higher PCE (10%) than that with only P3TAA hole-transporting material. In the ampholytic polythiophene (APT), on increasing pH, the morphology changes from the vesicle to fibrillar network for the dethreading of the PT chain, resulting in a red shift of the absorbance peak, an enormous increase in PL intensity, lowering of the charge transfer resistance, and an induction of Warburg impedance for the release of quencher I- ions. The PT-g-(PDMAEMA-co-PGLU-HEM) graft copolymer self-assembles with Con-A lectin, causing fluorescence quenching, and acts as a sensor for Con-A with a LOD of 57 mg/L. Varying sequences of the block copolymer containing pH-responsive PDMAEMA and temperature-responsive PDEGMEM grafted to the PT backbone shows different self-assembly, optical, electronic, and photocurrent properties depending on the proximity and preponderance of the block sequence on the PT backbone.

Organic Mixed Ion-Electron Conductivity in Polymer Hybrid Systems.

Recently, organic materials with mixed ion/electron conductivity (OMIEC) have gained significant interest among research communities all over the world. The unique ability to conduct ions and electrons in the same organic material adds to their use in next generation electrochemical, biotechnological, energy generation, energy storage, electrochromic, and sensor devices. Semiconducting conjugated polymers are well-known OMIECs due to their feasibility for both ion and electron transport in the bulk region. In this mini-review, we have shed light on conjugated polymers with ionic pendent groups, block copolymers of electronically and ionic conducting polymers, polymer electrolytes, blends of conjugated polymers with polyelectrolyte/polymer electrolytes; blends of conducting polymer with small organic molecules including conducting polymer-peptide conjugates; and blends of nonconjugated polymers as mixed conducting systems. These systems not only include the well-studied OMEIC systems, but also include some new systems where the OMEIC property has been predicted from the typical current-voltage (I-V) plots. The conduction mechanism of ions and electrons, ion-electron coupling, directionality, and dimensionality of these OMEIC materials are discussed in brief. The different properties of OMEIC materials and their applications in diverse fields like energy, electrochromic, biotechnology, sensing, and so forth are enlightened together with the perspective for future improvement of OMEIC materials.

Isomerization-Induced Excimer Formation of Pyrene-Based Acylhydrazone Controlled by Light- and Solvent-Sensing Aromatic Analytes.

Pyrene is a fluorescent polycyclic aromatic hydrocarbon, and it would be interesting to determine whether its C═N-based conjugate can be used for sensing of aromatic analytes at its supramolecular aggregated state. For this purpose, we have synthesized (E)-3,4,5-tris(dodecyloxy)-N'-(pyren-1-ylmethylene)benzohydrazide (Py@B) by alkylation, substitution, and the Schiff base reaction methodology. The E-isomer of Py@B (E-Py@B) exhibits a bright fluorescence due to excimer formation in nonaromatic solvents. Upon photoirradiation with λ = 254 nm, it exhibits E-Z isomerization across the C═N bond at a low concentration (10-4 M), resulting in a quenched fluorescence intensity, and interestingly, upon photoirradiation with λ = 365 nm, the Z-isomer of Py@B returns to the E-isomer again, indicating that E-Z isomerization of Py@B is reversible in nature. The thick supramolecular aggregated morphology of E-Py@B changes to a flowery needlelike morphology after photoirradiation with λ = 254 nm. The UV-vis absorption band at 370 nm for 10-4 M Py@B in methyl cyclohexane (MCH) is due to excimer formation for closer proximity of pyrene moieties present in E-Py@B and changes to the absorption peak at 344 nm for its Z-isomer formation. The fluorescence spectroscopy results also support the fact that the optimum concentration of the E-isomer of Py@B is 2 × 10-4 M in MCH for excimer formation. From spectral results, it may be concluded that nonaromatic solvents assist in constructing the excimer, but aromatic solvents resist forming an excimer complex of E-Py@B. The fluorescent emission of E-Py@B in MCH is quickly quenched on addition of different aromatic analytes through both static and dynamic pathways. In the solid state, E-Py@B also senses aromatic vapors efficiently via fluorescence quenching. Absorbance spectra of a model molecule obtained using time-dependent density functional theory (TDDFT) calculations on a DFT-optimized structure indicate complex adduct formation between E-Py@B and aromatic analytes from the well-matched theoretical and experimental UV-vis spectra on addition of different analytes with E-Py@B.

Reversible Stimuli-Dependent Aggregation-Induced Emission from a "Nonfluorescent" Amphiphilic PVDF Graft Copolymer.

A poly(vinylidine fluoride) graft random copolymer of t-butyl aminoethyl methacrylate (tBAEMA) and oligo(ethylene glycol) methyl ether methacrylate (OEGMA, Mn = 300) [PVDF-g-P(tBAEMA-ran-OEGMA), PVBO] is synthesized by atom transfer radical polymerization (ATRP), and PVBO is fractionated to get a highly water-soluble fraction (PVBO-1) showing a reversible on/off fluorescence behavior with gradual increase and decrease in pH, respectively, achieving a maximum quantum yield of 0.18 at pH = 12. PVBO-1 dissolved in water shows large multimicellar aggregates (MMcA), but at pH 12, crumbling of larger aggregates to much smaller micelles occurs, forming nonconjugated polymer dots (NCPDs), as supported by transmission electron microscopy and dynamic light scattering study. The reversible fluorescence on/off behavior also occurs with the decrease and increase of temperature. Theoretical study indicates that, at high pH, most of the amino groups become neutral and exhibit a strong tendency to form aggregates from crowding of a large number of carbonyl and amine groups, minimizing the HOMO-LUMO gap, showing an absorption peak at the visible region, and generating aggregation-induced emission.

Fluorescence in "Nonfluorescent" Polymers.

Recently, a great deal of research has been started on generating fairly strong photoluminescence from organic molecules without having any conjugated π-system or fluorophore. Discrete chromophores or auxochromophores termed as "subfluorophores" may undergo "space conjugation" via co-operative intramolecular conformation followed by intermolecular aggregation to generate fluorescence or sometimes phosphorescence emission. Polymeric materials are important in this regard as nonconjugated polymers self-assemble/aggregate in a moderately concentrated solution and also in the solid state, producing membranes, films, and so forth with good physical and mechanical properties. Therefore, promoting fluorescence in these commodity polymers is very much useful for sensing, organic light emitting diodes (OLED), and biological applications. In this perspective, we have discussed the aggregation-induced emission from four different types of architectures, for example, (i) dendrimers or hyperbranched polymers, (ii) entrapped polymeric micellar self-assembly, (iii) cluster formation, and (iv) stretching-induced aggregation, begining with the genesis of fluorescence from aggregation of propeller-shaped small organic molecules. The mechanism of induced fluorescence of polymers with subfluorophoric groups is also discussed from the theoretical calculations of the energy bands in the aggregated state. Also, an attempt has been made to highlight some useful applications in the sensing of surfactants, bacteria, cell imaging, drug delivery, gene delivery, OLED, and so forth.

A robust stimuli responsive Eu3+ - Metalo organic hydrogel and xerogel emitting white light.

Recently, there is incredible growth on optoelectronic properties of new supramolecular gels and white-light-emitting (WLE) metalo-organic gel comprised with single lanthanide metal ion having stimuli-responsive property is not yet reported. Here, we report a mandelic acid (MA)-triethylene tetraamine (TETA)-Eu-acetate conjugate (4.5:1:0.4 mol ratio), producing stimuli-sensitive WLE hydrogel exhibiting thermoreversible, thixotropic, pH-switchable, self-standing and self-healing properties. Energy minimized structure suggests complexation between MA-TETA conjugate and Eu3+ ion. Fluorescence intensity of MA-TETA conjugate decreases with increasing Eu3+ concentration indicating energy transfer from MA-TETA to Eu3+. Decay of donor fluorescence intensity follows Stern-Volmer equation and energy transfer efficiency is 42%. WLE gel has Quantum yield 11.4% and Förster distance 1.7 Å. Hydrogel and xerogel show WLE on excitation at 330 and 350 nm having CIE coordinates (0.34, 0.33) and (0.28, 0.32), respectively. WLE gel has Correlated colour temperature 5148 K, appropriate for cool day light emission and on coating over UV-LED bulb it emits bright white light.

A review on recent advances in polymer and peptide hydrogels.

In this review, we focus on the very recent developments on the use of the stimuli responsive properties of polymer hydrogels for targeted drug delivery, tissue engineering, and biosensing utilizing their different optoelectronic properties. Besides, the stimuli-responsive hydrogels, the conducting polymer hydrogels are discussed, with specific attention to the energy generation and storage behavior of the xerogel derived from the hydrogel. The electronic and ionic conducting gels have been discussed that have applications in various electronic devices, e.g., organic field effect transistors, soft robotics, ionic skins, and sensors. The properties of polymer hybrid gels containing carbon nanomaterials have been exemplified here giving attention to applications in supercapacitors, dye sensitized solar cells, photocurrent switching, etc. Recent trends in the properties and applications of some natural polymer gels to produce thermal and acoustic insulating materials, drug delivery vehicles, self-healing material, tissue engineering, etc., are discussed. Besides the polymer gels, peptide gels of different dipeptides, tripeptides, oligopeptides, polypeptides, cyclic peptides, etc., are discussed, giving attention mainly to biosensing, bioimaging, and drug delivery applications. The properties of peptide-based hybrid hydrogels with polymers, nanoparticles, nucleotides, fullerene, etc., are discussed, giving specific attention to drug delivery, cell culture, bio-sensing, and bioimaging properties. Thus, the present review delineates, in short, the preparation, properties, and applications of different polymer and peptide hydrogels prepared in the past few years.

Zwitterionic Poly(vinylidene fluoride) Graft Copolymer with Unexpected Fluorescence Property.

Recently, there has been a growth of research on the nonconjugated polymer exhibiting fluorescence property and it would be exciting if fluorescence property is developed in zwitterionic polymers because of their good water solubility. Poly(vinylidene fluoride) (PVDF) grafted with poly(dimethyl amino ethyl methacrylate) (PDMAEMA) is fractionated and a highly water-soluble fraction (PVDM-1) is quaternized with 1,3-propane sultone, producing a zwitterionic polymer, PVDF- g-PDMAEMA-sultone (PVDMS). PVDM-1 shows the fluorescence property with very low quantum yield (1%) in water, but on quaternization, fluorescence quantum yield increases to 8%. Transmission electron microscopy results indicate that the PVDM-1 cast from water has vesicular morphology, whereas PVDMS exhibits aggregated vesicular morphology. The 1H NMR spectra indicate the presence of 72 mol % DMAEMA in PVDM-1 wherein 66% of -NMe2 groups is quaternized upon postpolymerization modification. PVDM-1 exhibits absorption peaks at 210, 276, and 457 nm with a hump at 430 nm, whereas PVDMS exhibits two absorption peaks at 203 and 297 nm. PVDM-1 exhibits a broad emission peak at 534 nm, whereas PVDMS exhibits a sharp emission peak at 438 nm. An attempt has been made from density functional theory calculations to shed light on the origin of fluorescence in both PVDM-1 and in the zwitterionic PVDMS. The excitonic decay occurs from the lowest unoccupied molecular orbital (LUMO) of carbonyl group to the highest occupied molecular orbital (HOMO) of tertiary amine group for PVDM-1, whereas in PVDMS, the excitonic transition occurs from the LUMO situated over the quaternary ammonium group to the HOMO located on the electron-rich terminal sulfonate group.

Light-Induced Conformational Change of Uracil-Anchored Polythiophene-Regulating Thermo-Responsiveness.

Tuning the electronic structure of a π-conjugated polymer from the responsive side chains is generally done to get desired optoelectronic properties, and it would be very fruitful when light is used as an exciting tool that can also affect the backbone chain conformation. For this purpose, polythiophene- g-poly-[ N-(6-methyluracilyl)- N, N-dimethylamino chloride]ethyl methacrylate (PTDU) is synthesized. On exposure to diffuse sunlight, the uracil moieties of the grafted chains cause the absorption maximum of PTDU solution to show gradual blue shift of 87 nm and a gradual blue shift of 46 nm in the emission maximum, quenching its fluorescence with time. These effects occur specifically at the absorption range of polythiophene (PT) chromophore on direct exposure of light of different wavelengths, and the optimum wavelength is found to be 420 nm. Impedance study suggests a decrease in charge transfer resistance upon exposure because of conformational change of PTDU. Theoretical study indicates that on exposure to visible light, uracil moieties move toward the backbone to facilitate photoinduced electron transfer between the PT and the uracil, attributing to the variation in optoelectronic properties. Morphological and light-scattering studies exhibit a decrease in particle size because of coiling of the PT backbone and squeezing of the grafted chain on light exposure. The transparent orange-colored PTDU solution becomes hazy with a hike in emission intensity on addition of sodium halides and becomes reversibly transparent or hazy on heating or cooling. The screening of cationic centers of PTDU by varying halide anion concentration tunes the phase transition temperature. Thus, the light-induced variation in the backbone conformation is responsible for tuning the optoelectronic properties and regulates the thermos-responsiveness of the PTDU solution in the presence of halide ions.

Injectable Hydrogel of Vitamin B9 for the Controlled Release of Both Hydrophilic and Hydrophobic Anticancer Drugs.

Folic acid (FA), vitamin B9 , is a good receptor of drugs triggering cellular uptake via endocytosis. FA is sparingly soluble in water. Herein, a new approach for the formation of FA hydrogel by the hydrolysis of glucono-δ-lactone in PBS buffer under physiological conditions has been reported. The gel has a fibrillar network morphology attributable to intermolecular H-bonding and π-stacking interactions. The thixotropic property of the gel is used for the encapsulation of both hydrophilic [doxorubicin (DOX)] and hydrophobic [camptothecin (CPT)] drugs. The loading of DOX and CPT into the gel is attributed to the H-bonding interaction between FA and drugs. The release of DOX is sustainable at pH 4 and 7, and the Peppas model indicates that at pH 7 the diffusion of the drug is Fickian but it is non-Fickian at pH 4. The release of CPT is monitored by fluorescence spectroscopy, which also corroborates the combined release of both drugs. The metylthiazolyldiphenyltetrazolium bromide assay of FA hydrogel demonstrates nontoxic behavior and that the cytotoxicity of the DOX-loaded FA hydrogel is higher than that of pure DOX, with a minimal effect on normal cells.

Quantum-Dot-Mediated Controlled Synthesis of Dual Oxides of Molybdenum from MoS2 : Quantification of Supercapacitor Efficacy.

The versatile technological applications of molybdenum oxides requires the efficient synthesis of various stoichiometric molybdenum oxides. Thus, herein, a controlled method to synthesize both MoO3 and MoO2 from MoS2 via quantum dot intermediates is reported. Microscopic, spectroscopic, and X-ray studies corroborate the formation of orthorhombic α-MoO3 with a microbelt structure and monoclinic MoO2 nanoparticles that self-assemble into hollow tubes. Quantitative investigations into charge-storage kinetics reveal that MoO2 exhibits an excellent pseudocapacitive response up to a mass loading of 5 mg cm-2 with an areal capacity of 327.2 mC cm-2 at 5 mV s-1 , with 41.9 % retention at 100 mV s-1 . In contrast, above a mass loading of 0.5 mg cm-2 , the charge-storage nature of MoO3 electrodes switches from that of a supercapacitor to battery type. At a sweep rate of 50 mV s-1 , 87.2 % of the total charge is contributed by a capacitive response in a 1 mg cm-2 MoO2 electrode. The charge-storage kinetics of MoO3 and MoO2 reflect on the respective asymmetric supercapacitors. A MoO2 //graphite asymmetric supercapacitor holds an outstanding energy density of 341 mW h m-2 at a power density of 4949 mW m-2 and delivers an ultrahigh power density of 28140 mW m-2 with an energy density 142 mW h m-2 and energy efficiency of 87 %.

Copolymers of poly(3-thiopheneacetic acid) with poly(3-hexylthiophene) as hole-transporting material for interfacially engineered perovskite solar cell by modulating band positions for higher efficiency.

In order to tune the band positions of the hole-transporting material (HTM) in an interfacially engineered perovskite solar cell (PSC), random copolymers of poly(3-thiopheneacetic acid) and poly(3-hexylthiophene) (P3TAA-co-P3HT) with different compositions were produced by oxidative polymerization. The copolymers were characterized using 1H NMR, FTIR, and UV-vis spectroscopy and gel permeation chromatography. Here, ZnO nanoparticles were used as the electron-transporting material (ETM) and methylammonium lead iodide (MAPbI3) perovskite was used as the light-absorbing material to form an FTO/ZnO/MAPbI3/copolymer/Ag device, of which the power conversion efficiency (PCE) was found to be dependent on the copolymer composition and reached a maximum (∼10%) at a P3TAA content of 43 mol% in the copolymer (P3). The band gaps of the copolymers as determined from UV-vis spectroscopy and cyclic voltammetry exhibit a staggered-gap hetero-interface configuration in which the HOMO and LUMO of P3 closely match those of MAPbI3 and give rise to the maximum PCE. Time-resolved photoluminescence spectra of MAPbI3/HTM samples indicate that charge transfer across the perovskite/copolymer interface was faster with a reduced recombination rate for a P3 sample. The electrochemical impedance spectra (EIS) of the PSCs exhibit Nyquist plots with two semicircles, which correspond to an equivalent circuit consisting of two parallel R-C and R-CPE circuits connected in series. Analysis of the data indicates that the effective electron lifetime was longest for the P3 copolymer, which indicates that the charge recombination was lower than that in the components and other copolymers. The copolymers exhibited an intermediate stability with respect to their components, and amongst the copolymers P3 exhibited the highest stability.

Optoelectronic Properties of Self-Assembled Nanostructures of Polymer Functionalized Polythiophene and Graphene.

In this Feature Article, we discuss the variation of optoelectronic properties with the aggregation style of polythiophene (PT) graft copolymers and polymer-modified graphene systems. Grafting of flexible polymers on a PT chain exhibits several self-organized patterns under various conditions, causing different optical and electronic properties, arising from the different conformational states of the conjugated chain. Graphene, a zero band gap material, is functionalized with polymers both covalently and noncovalently to create a finite band gap importing new optoelectronic properties. The polymer-triggered self-assembled nanostructures of PT and graphene-based materials bring unique optical/electronic properties suitable for sensing toxic ions, nitroaromatics, and surfactants, for drug delivery, and also for fabricating molecular logic gates, electronic rectifiers, photocurrent devices, etc.

Triarylamine-Cored Dendritic Molecular Gel for Efficient Colorometric, Fluorometric, and Impedometeric Detection of Picric Acid.

Detection of nitroaromatics at ultralow concentration is a major security concern in defense, forensics, and environmental science. To this end, a new triarylamine-cored dendritic gelator (OGR) was synthesized, which produced thermoreversible, thixotropic, and fluorescent gels in n-octanol. On gelation, both π-π* transitions and the emission peak of the gelator show redshifts with a 4.5-fold increase of fluorescence intensity in the gel state indicating J-aggregation. The nitrogen lone-pair electrons of OGR make it a donor, and electron transfer occurs to acceptor nitroaromatics causing fluorescence quenching, which is further promoted due to its acidity. The Stern-Volmer rate constants measured for different nitroaromatics showed that it senses picric acid (PA) best. The contact-mode technique with OGR-treated paper strips can allow naked-eye detection of PA under UV light down to 10-11 m concentration within 30 s. Reusability of the gel is achieved by treating OGR@PAx with NaOH solution. Impedance spectroscopic results indicated a decrease of both charge-transport resistance and Warburg impedance on successive addition of PA. The limits of detection of PA determined from fluorescence and impedance measurements match well. Thus, the OGR gel is a reusable, low-cost, specific sensor for PA by naked-eye colorimetric, fluorescence, and impedance techniques.

A New Facile Synthesis of Tungsten Oxide from Tungsten Disulfide: Structure Dependent Supercapacitor and Negative Differential Resistance Properties.

Tungsten oxide (WO3 ) is an emerging 2D nanomaterial possessing unique physicochemical properties extending a wide spectrum of novel applications which are limited due to lack of efficient synthesis of high-quality WO3 . Here, a facile new synthetic method of forming WO3 from tungsten sulfide, WS2 is reported. Spectroscopic, microscopic, and X-ray studies indicate formation of flower like aggregated nanosized WO3 plates of highly crystalline cubic phase via intermediate orthorhombic tungstite, WO3. H2 O phase. The charge storage ability of WO3 is extremely high (508 F g-1 at current density of 1 A g-1 ) at negative potential range compared to tungstite (194 F g-1 at 1 A g-1 ). Moreover, high (97%) capacity retention after 1000 cycles and capacitive charge storage nature of WO3 electrode suggest its supremacy as a negative electrode of supercapacitors. The asymmetric supercapacitor, based on the WO3 as a negative electrode and mildly reduced graphene oxide as a positive electrode, manifests high energy density of 218.3 mWhm-2 at power density 1750 mWm-2 , and exceptionally high power density, 17 500 mW m-2 , with energy density of 121.5 mWh m-2 . Furthermore, the negative differential resistance (NDR) property of both WO3 and WO3 .H2 O are reported for the first time and NDR is explained with density of state approach.

Influence of Chain Length on the Self-Assembly of Poly(ε-caprolactone)-Grafted Graphene Quantum Dots.

The multifarious applications of graphene quantum dots (GQDs) necessitate surface modifications to enhance their solution processability. Herein, we report the synthesis and self-assembly of GQDs grafted with poly(ε-caprolactone) (PCL) of different degrees of polymerization (3, 7, 15, and 21) produced from ring-opening polymerization. Optical and morphological studies unveil the transformation of the assemblies from J-aggregates to H-aggregates, accompanied by an alteration in morphology from toroid to spheroid to rodlike structures with increasing chain length of PCL. Functionalized GQDs with lower chain lengths of PCL at higher concentration also assemble into liquid-crystalline phases as observed from birefringent textures, which are later correlated to the formation of columnar hexagonal (Colh) mesophases. However, no such behavior is observed at higher chain lengths of PCL under identical conditions. Therefore, it is evident that the variation in the PCL chain length plays a crucial role in the self-assembly, which is primarily triggered by the van der Waals force between the polymer chains dictating the π stacking of GQDs, resulting in different self- aggregated behavior.

Influence of Hofmeister I- on Tuning Optoelectronic Properties of Ampholytic Polythiophene by Varying pH and Conjugating with RNA.

A significant tuning of optoelectronic properties of polythiophene (PT) chains due to Hofmeister iodide (I-) ion is demonstrated in ampholytic polythiophene [polythiophene-g-poly{(N,N,N-trimethylamino iodide)ethyl methacrylate-co-methacrylic acid}, APT] at different pHs. In acidic medium, the absorption and emission signals of PT chromophore exhibit appreciable blue shift in the presence of I- as counteranion only. The cooperative effect of undissociated -COOH and quaternary ammonium groups immobilize I- near the apolar PT chain causing threading of grafted chains and hence twisting of the backbone attributing to the blue shift. As medium pH is increased, dethreading of the PT backbone occurs due to ionization of -COOH group, releasing quencher iodide ions from the vicinity of the PT chains resulting in a red shift in absorption and a sharp hike in fluorescence intensity (390 times) for an increase of excitons lifetime. With an increase of pH, morphology changes from a multivesicular aggregate with vacuoles to smaller size vesicles and finally to nanofibrillar network structure. Dethreading is also found when APT interacts with RNA showing a significant hike of fluorescence (22 times) for displacing iodide ions forming a nanofibrillar network morphology. Threading and dethreading also affect the resistance, capacitance, and Warburg impedance values of APT. Molecular dynamics simulation of a model APT chain in a water box supports the threading at lower pH where the iodide ions pose nearer to the PT chain than that at higher pH causing dethreading. So the influence of Hofmeister I- ion is established for tuning the optoelectronic properties of a novel PT based polyampholyte by changing pH or by conjugating with RNA.

Deciphering the Effect of Polymer-Assisted Doping on the Optoelectronic Properties of Block Copolymer-Anchored Graphene Oxide.

Doping facilitates the tuning of band gap, providing an opportunity to tailor the optoelectronic properties of graphene in a simple way, and polymer-assisted doping is a new route to combine the optoelectronic properties of graphene with the properties of a polymer. In this endeavor, a linear diblock copolymer, polycaprolactone-block-poly(dimethyl aminoethyl methacrylate) (PCL13-b-PDMAEMA117) (GPCLD) is grafted from the graphene oxide (GO) surface via consecutive ring opening and atom transfer radical polymerization. GPCLD is characterized using proton nuclear magnetic resonance (1H NMR), Fourier transform infrared spectroscopy, atomic force microscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, and Raman spectroscopy. The phase transition behavior of the GPCLD solution with varying temperature and pH is monitored using fluorescence spectroscopy and dynamic light scattering. Temperature-dependent 1H NMR spectra at pH 9.2 indicate the influence of temperature on the interaction between GPCLD and solvent (water) molecules causing the phase separation. Fluorescence spectra at pH 4 and 9.2 give the evidence of localized p- and n-type doping of graphene assisted by the pendent PDMAEMA chains. In the impedance spectra of GPCLD films, the Nyquist plots vary with pH; at pH 4, they exhibit a semicircle at higher frequencies and a spike at lower frequencies; at pH 7.0, the spike is replaced by an arc; and at pH 9.2, the semicircle at higher frequencies vanishes and only a spike is noticed, all of these suggesting different types of doping of graphene at different pH values. The dc-conductivity also varies with pH and temperature because of the different types of doping. The current (I)-voltage (V) property of GPCLD at different pH values is very unique: at pH 9.2, an interesting feature of negative differential resistance (NDR) is observed; at pH 7, the rectification property is observed; and at pH 4, again the NDR property is observed. The temperature-dependent I-V property at pH 7 and 9.2 clearly indicates a signature of doping, dedoping, and redoping because of the change in the interaction of GO with the grafted polymer arising from coiling and decoiling of polymer chains.

An insight into the hybrid dye-sensitized solar cell from polyaniline-CdS nanotubes through impedance spectroscopy.

Composites of polyaniline (PANI) and cadmium sulfide nanoparticles (CdS NPs) are in situ synthesized by polymerizing aniline in acetic acid medium for different concentrations of CdS NPs. The composites, characterized by scanning and transmission electron microscopy, exhibit nanotubular morphology of PANI decorated with nanospheres of CdS NPs at their outer surface. The FTIR and UV-vis spectra indicate strong interaction between PANI and the CdS NPs suggesting a good conjugate for photovoltaic applications. The dc conductivities of the composite increase with an increase of the CdS concentration showing a maximum of 1.17 × 10-2 S cm-1 for the C200 sample (obtained by polymerizing 182 µL aniline with 200 mg CdS). The current-voltage plots indicate that the photocurrent is higher from the dark current and the separation between the dark current and photocurrent is maximum in C200. The effectiveness of these composites in DSSCs is studied under illumination of 100 mW cm-2 and the C200 device exhibits a maximum open circuit voltage of 0.73 V, a short circuit current of 8.22 mA cm-2, and a power conversion efficiency of 3.96%. The impedance study of the cells indicates that the lifetime of the photo-injected electrons is highest (1.34 ms) for the C200 sample, explaining the maximum PCE among the composites.

Enhancement of Energy Storage and Photoresponse Properties of Folic Acid-Polyaniline Hybrid Hydrogel by in Situ Growth of Ag Nanoparticles.

Electrically conductive hydrogels are a fascinating class of materials that exhibit multifarious applications such as photoresponse, energy storage, etc., and the three-dimensional micro- and nanofibrillar structures of the gels are the key to those applications. Herein, we have synthesized a hybrid hydrogel based on folic acid (F) and polyaniline (PANI) in which F acts as a supramolecular cross-linker of PANI chains. The gels are mechanically robust and are characterized by field-emission scanning electron microscopy, transmission electron microscopy, and spectroscopic, rheological, and universal testing measurements. The hybrid xerogel exhibit a BET surface area 238 m2 g-1, conductivity of 0.04 S/cm, specific capacitance of 295 F/g at a current density of 1A/g, and photocurrent of ∼2 mA under white-light illumination. Silver nanoparticles (AgNPs) are in situ grown to elegantly improve the conductivity, energy storage, and photoresponse capability of the gels. The formation of AgNPs drastically improves the specific capacitances up to 646 F/g (at current density 1A/g), excellent rate capability (403 F/g at 20 A/g), and stable cycling performance with a retention ratio of 74% after 5000 cycles. The AgNPs embedded gel exhibits dramatic enhancement of photocurrent to 56 mA, and its time-dependent photoillumination corroborates faster rise and decay of current compared to those of folic acid-polyaniline hydrogel.