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.

We report a general strategy for fine-tuning the bandgap of donor-acceptor-donor based organic molecules by modulating the electron-donating ability of the donor moiety by changing the benzochalcogenophene donor groups from benzothiophenes to benzoselenophenes to benzotellurophenes. These molecules show red-shifts in absorption and external quantum efficiency maxima from sulfur to selenium to tellurium. In bulk heterojunction solar cell devices, the benzoselenophene derivative shows a power conversion efficiency as high as 5.8% with PC61BM as the electron acceptor.

Charge trapping and storage in polymer dielectrics can be harnessed to control semiconductor devices. Organic transistor (OFET) gate insulators affect bias stress and threshold voltage (V th), and charging them can preset the operating voltages and control bias stress. We describe a chemical design and film fabrication procedure for construction of stacks of polystyrene (PS) layers, each with arbitrary concentrations of potentially chargeable functional groups. Thermal cross-linking of benzocyclobutene subunits ensures layer integrity while keeping the layers free of polar functionality and small molecule byproducts. Neutron reflectivity (NR), scanning electron microscopy, and atomic force microscopy (AFM) showed that individual layer thicknesses varied systematically with polymer concentration in deposition solutions, and interfacial thicknesses ranged from 1.5 to 4 nm, independent of layer thickness, demonstrating formation of distinct layers with minimal roughness or intermixing. The PS-based materials were used as the sole gate dielectrics for pentacene OFETs. We compared V th before and after charging. Increased bias stress stability as evidenced by reduced V th shift was seen in devices with trilayer dielectrics with substituted PS as the middle layer compared to a dielectric made from unsubstituted PS. On the other hand, increased V th shift was seen in many devices with bilayer dielectrics made with substituted PS as the top layer. We attribute the decreased V th shift seen in trilayer devices to an increased dielectric polarization of the substituted PS in the middle layer that countered the charge trapping effect in the top layer. This demonstration establishes a method for utilizing vertical charge patterns for various electronics applications.

b S Supporting Information S olution processable organic semiconductors have generated tremendous interest because of their applicability in organic microelectronics, light-emitting diodes, and photovoltaics. 1-6 Both p-type and n-type materials, with commensurate mobilities, are required for effective functioning of many of these devices. Significant progress has been made in the development of materials possessing high charge mobilities with materials based on heteroaromatic molecules, especially thiophenes. Whereas thiophene-based materials are often p-type materials, 7,8 it has been shown that the incorporation of fluorinated substituents as terminal functionalities causes these materials to exhibit n-type characteristics. 9-15 This behavior has often been attributed to the lowering of LUMO energy level, making electron injection easier and hence imparting n-type character to the molecule. 11,13 However, it is not clear whether the factors underlying stabilization of frontier orbital energy levels have correlations to the transport of the injected charges. We were interested in testing this issue with a molecular scaffold that satisfies the following design criteria: (i) changing the hydrocarbon substituent to a fluorocarbon substituent should have minimal effect on the frontier orbital energy level and (ii) the scaffold allows for tuning the frontier orbital energy level independent of the fluorocarbon substituent. For this purpose, we report here the design, syntheses, and charge transport characteristics of solution-processable systems based on cyclopenta[2,1-b:3,4-b 0 ]dithiophene.The cyclopenta[2,1-b:3,4-b 0 ]dithiophene, referred here as simply cyclopentadithiophene (CPD), unit can be said to be a combination of structural motifs found in fluorenes and oligothiophenes. The rigid fused ring structure in this molecule lowers the reorganization energy, a parameter that strongly affects the rate of intermolecular charge hopping and therefore the charge carrier mobility in organic semiconductors. 16 The CPD unit has two locations where substituents can be incorporated: (a) the R-positions in the thiophenes, where hydrocarbon or fluorocarbon substituents can be incorporated, and (b) the bridgehead position, where substituents can be incorporated to alter significantly the frontier orbital energy levels. In fact, it has been shown previously that variations at these positions in such fused thiophene structures can be used to tune the frontier orbital energy levels. [17][18][19] The molecules that satisfy our design criteria and potentially address the issue in hand are shown in Chart 1. The CPD core is functionalized at the bridgehead position with the electronwithdrawing carbonyl or dicyanomethylene functionality, whereas the R-positions are substituted with either phenyl or pentafluorophenyl moieties. Installation of electron-withdrawing functionalities, such as carbonyl group, at the bridgehead position of the CPD leads to lowering of bandgap, which has been attributed to the stabilization of the quinoid fo...