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The ability to control the bulk and interfacial polarization of dielectric polymers is important to their application in organic electronics. We examine the effect of the trifluoromethyl substituent on poly(3-trifluoromethylstyrene) (P3TFMS) as compared to unsubstituted polystyrene (PS) on the I-V relationships of pentacene-based organic field-effect transistors (OFETs). Single- and double-layered films of these polymers were used, with lower layers crosslinked through vinylbenzocyclobutene comonomers before deposition of upper layers. Control experiments verified that the electronic effect of the crosslinking was negligible. We found that the TFM substituent markedly and independently affected both the initial threshold voltage Vth and the nonvolatile, shifted Vth observed after the application of static gate voltage, depending on its position adjacent or apart from the pentacene. The trifluoromethyl-bearing polymers exhibited significantly lower magnitude initial threshold voltages ( V t h , i of ca. −17 V for P3TFMS compared to −35 V for PS), large threshold voltage shifts after charging by the application of static electric fields (Δ V t h of ca. 32 V for P3TFMS and 17 V for PS), and greater stability of the Δ V t h under repeated charge/discharge cycles. These results are consistent with P3TFMS having fewer interfacial trap states but more stable bulk trap states. The results are applicable to organo-electronic systems such as piezoelectrics for energy harvesting and nonvolatile OFETs such as memory, sensing, and logic elements. [ABSTRACT FROM AUTHOR]

Peptide nanostructures with built-in electronic functions offer a new platform for biomaterial science. In this report, we interrogate the influences of the immediate peptide environment around oligo(p-phenylenevinylene) (OPV3) electronic units embedded within one-dimensional peptide nanostructures on the resulting photophysics as assessed by UV-vis, photoluminescence (PL), and circular dichroism spectroscopies. To do so, we studied peptide-core-peptide molecules where the core was either OPV3 or an aliphatic n-decyl chain. Coassemblies of these molecules wherein the π-core was diluted as a minority component within a majority aliphatic matrix allowed for the variation of interchromophore exciton coupling commonly found in homoassemblies of peptide-OPV3-peptide monomers. Upon coassembly of the peptides, a hydrophilic tripeptide sequence (Asp-Asp-Asp-, DDD-) promoted the dilution/isolation of the peptide-π-peptide molecules in the majority peptide-decyl-peptide matrix whereas a hydrophobic tripeptide sequence (Asp-Val-Val-, DVV-) promoted the formation of self-associated stacks within the nanostructures. We also performed temperature variation studies to induce the reorganization of π-electron units in the spatially constrained n-decyl environment. This study elucidates the nonresonant (e.g., conformational) and local peptide field effects enforced within the internal environment of peptide nanomaterials and how they lead to varied photophysical properties of the embedded π-electron cores. It offers new insights on tuning the optoelectronic properties of these types of materials on the basis of the local electronic and steric environment available within the nanostructures. [ABSTRACT FROM AUTHOR]

Peptide-π-peptide triblock molecules can self-assemble into 1-D nanostructures with extensive hydrogen-bonding networks under appropriate pH conditions. These materials are of interest due to the embedded π-electron units that can facilitate energy and charge transport within biocompatible peptide matrices. Interactions among amino acid residues presented along these hydrogen-bonded structures lead to hierarchical bundling into larger fibrillar assemblies. This complicates the analysis of individual fibrils, an understanding of which is important for tailoring the functionality of the resulting nanomaterials. Appending large bulky groups onto the peptides should frustrate these bundling interactions and significantly alter the self-assembly behavior by restricting the formation of higher order assemblies. Here we evaluate the self-assembly behavior of peptide-π-peptide molecules appended with poly(alkyl ether) dendrons containing tetraethylene glycol functionalities. These dendrons render the peptide-dendron hybrid (PDH) molecules incapable of assembly under conditions that typically promote assembly of the parent peptides. However, 1,1,1,3,3,3-hexafluoro-2-propanol, a fluorinated alcohol known to denature proteins, triggers the aqueous assembly of the PDH molecules, thus yielding platelike nanostructures with narrow size distributions. This presents a new methodology for generating self-assembled nanostructures from peptide-π-peptide materials and provides an opportunity for orthogonal functionalization using motifs with varying degrees of hydrophilicity and functions. The effects of peptide sequence and dendron position along the peptide backbone on the assembly behavior were investigated using UV-vis, photoluminescence, and circular dichroism spectroscopies, and the morphologies of the resulting self-assembled nanostructures were investigated using transmission electron microscopy. [ABSTRACT FROM AUTHOR]

The co-assembly behavior of peptide-π-peptide and peptide-alkyl-peptide triblock molecules that form one-dimensional (1D) nanostructures under acidic, aqueous environments is dependent on the peptide sequence and the torsional constraints imposed within the nanomaterial volume. Although a hydrophilic tripeptide sequence (Asp-Asp-Asp, DDD-) previously promoted isolation/dilution of minority π-electron components in the matrix of aliphatic peptides, a β-sheet promoting sequence (Asp-Val-Val, DVV-) led to blocks of the two components distributed within larger 1D self-assembled nanostructures. Furthermore, torsional restrictions exerted on the oligoaromatic π-electron unit by the self-assembly process can lead to changes in its conformation (for example, planarity), which has ramifications on its functionality within the peptide matrix. Here, we study this impact on thiophene-based π-electron units with inherently different geometries, viz., relatively planar 2,2':5',2″:5″,2‴-quaterthiophene and 3″,4'-dimethyl-2,2':5',2″:5″,2‴-quaterthiophene, which is twisted at the core bithiophene unit due to the presence of two methyl groups. These peptides were co-assembled at 5 and 20 mol % with peptide- n-decyl-peptide triblock molecules, and the resultant assemblies were studied using UV-vis absorption, photoluminescence, and circular dichroism spectroscopies. We found that torsional restriction in dimethylated quaterthiophene units can impact the stacking behavior of these 1D peptide nanoassemblies and have consequences on their photophysical properties. Additionally, these insights help in the understanding of the dependence of the optoelectronic properties of these materials on both the intrinsic conformation of π-units and the geometric constraints imposed by their immediate local environment under aqueous conditions.

Peptides provide a biomolecular scaffold for solubilizing and assembling π-conjugated molecules in aqueous media. The properties of such peptide-π chromophore conjugates can be manipulated by varying the constituent amino acid residues in the peptide backbone as well as the chromophore moieties. Such a precise handle on molecular structure leads to molecules with diverse macromolecular and material properties. We developed a versatile synthetic protocol that leads to a wide range of peptide-π chromophore conjugates in which the chromophores are covalently attached to the peptide backbone such that the chromophore is flanked by two peptide chains. This "trimer" structure lends interesting self-assembly properties to these materials which may be useful for a plethora of biological applications.

NO 2 -responsive polymer-based organic field-effect transistors (OFETs) are described, and room-temperature detection with high sensitivity entirely from the semiconductor was achieved. Two thiophene polymers, poly(bisdodecylquaterthiophene) and poly(bisdodecylthioquaterthiophene) (PQT12 and PQTS12, respectively), were used as active layers to detect a concentration at least as low as 1 ppm of NO 2 . The proportional on-current change of OFETs using these polymers reached over 400% for PQTS12, which is among the highest sensitivities reported for a NO 2 -responsive device based on an organic semiconducting film. From measurements of cyclic voltammetry and the electronic characteristics, we found that the introduction of sulfurs into the side chains induces traps in films of the PQTS12 and also decreases domain sizes, both of which could contribute to the higher sensitivity of PQTS12 to NO 2 gas compared with PQT12. The ratio of responses of PQTS12 and PQT12 is higher for exposures to lower concentrations, making this parameter a means of distinguishing responses to low concentrations for extended times from exposures to high concentrations from shorter times. The responses to nonoxidizing vapors were much lower, indicating good selectivity to NO 2 of two polymers. This work demonstrates the capability of increasing selectivity and calibration of OFET sensors by modulating redox and aggregation properties of polymer semiconductors.

We present a completely solid-phase synthetic strategy to create three- and four-fold peptide-appended π-electron molecules, where the multivalent oligopeptide presentation is dictated by the symmetries of reactive handles placed on discotic π-conjugated cores. Carboxylic acid and anhydride groups were viable amidation and imidation partners, respectively, and oligomeric π-electron discotic cores were prepared through Pd-catalyzed cross-couplings. Due to intermolecular hydrogen bonding between the three or four peptide axes, these π-peptide hybrids self-assemble into robust one-dimensional nanostructures with high aspect ratios in aqueous solution. The preparation of these systems via solid-phase methods will be detailed along with their self-assembly properties, as revealed by steady-state spectroscopy and transmission electron microscopy and electrical characterization using field-effect transistor measurements., Competing Interests: The authors declare no competing financial interest.

Perylenediimide-pentathiophene systems with varied architecture of thiophene units were synthesized. The photophysical, electrochemical, and charge transport behavior of the synthesized compounds were studied. Both molecules showed a low band gap of ∼1.4 eV. Surprisingly, the molecule with pentathiophene attached via β-position to the PDI unit upon annealing showed a predominant hole mobility of 1 × 10(-4) cm(2) V(-1) s(-1) whereas the compound with branched pentathiophene attached via β-position showed an electron mobility of 9.8 × 10(-7) cm(2) V(-1) s(-1). This suggests that charge transport properties can be tuned by simply varying the architecture of pentathiophene units.

Amphiphilic molecules self-assemble in solvents because of the differential solvation of the hydrophilic and lipophilic functionalities. Small-molecule surfactants have long been known to form micelles in water that can solubilize lipophilic guest molecules in their water-excluded interior. Polymeric surfactants based on block copolymers are also known to form several types of aggregates in water owing either to the mutual incompatibility of the blocks or better solvation of one of the blocks by the solvent. Incorporating amphiphilicity at smaller length scales in polymers would provide an avenue to capture the interesting properties of macromolecules and fine tune their supramolecular assemblies. To address this issue, we designed and synthesized amphiphilic homopolymers containing hydrophilic and lipophilic functionalities in the monomer. Such a polymer can be imagined to be a string of small-molecule surfactants tethered together such that the hydrophilic and lipophilic functionalities are located on opposite faces, rendering the assemblies facially amphiphilic. This feature article describes the self-assembly of our amphiphilic homopolymers in polar and apolar solvents. These homopolymers not only form micelles in water but also form inverse micelles in organic solvents. Subtle changes to the molecular structure have been demonstrated to yield vesicles in water and inverted micelles in organic solvents. The characterization of these assemblies and their applications in separations, catalysis, and sensing are described here.