Small organic molecules with strong intermolecular interactions have a wide range of desirable optical and electronic properties and rich phase behaviors. Incorporating them into block copolymer (BCP)-based supramolecules opens new routes to generate functional responsive materials. Using oligothiophene-containing supramolecules, we present systematic studies of critical thermodynamic parameters and kinetic pathway that govern the coassemblies of BCP and strongly interacting small molecules. A number of potentially useful morphologies for optoelectronic materials, including a nanoscopic network of oligothiophene and nanoscopic crystalline lamellae, were obtained by varying the assembly pathway. Hierarchical coassemblies of oligothiophene and BCP, rather than macrophase separation, can be obtained. Crystallization of the oligothiophene not only induces chain stretching of the BCP block the oligothiophene is hydrogen bonded to but also changes the conformation of the other BCP coil block. This leads to an over 70% change in the BCP periodicity (e.g., from 31 to 53 nm) as the oligothiophene changes from a melt to a crystalline state, which provides access to a large BCP periodicity using fairly low molecular weight BCP. The present studies have demonstrated the experimental feasibility of generating thermoresponsive materials that convert heat into mechanical energy. Incorporating strongly interacting small molecules into BCP supramolecules effectively increases the BCP periodicity and may also open new opportunities to tailor their optical properties without the need for high molecular weight BCP.

Polymer-fullerene based photovoltaic devices have attracted a great deal of attention based on the potential for realizing low-cost, solution-processable, and flexible solar cells. 1 Recently, power conversion efficiencies in excess of 5% have been reported for the poly(3-hexylthiophene)/[6,6]-phenyl-C 61 butyric acid methyl ester (P3HT:PCBM) bulk heterojunction (BHJ) solar cell. 2 The successful combination of P3HT and PCBM is based on the ability of the two components to mix homogenously in a pristine cast film and then, under the influence of thermal or solvent annealing, 3,4 undergo a controlled phase segregation yielding a nanometer length scale bicontinuous network of highly ordered donor and acceptor phases, suitable for charge transport. 2 Much effort has been dedicated to the optimization of these devices, including a focus on developing a deeper understanding of the role of polythiophene structure on device performance. [5][6][7][8][9][10] The ability of regioregular (RR) P3HT to form crystalline phases with strong interchain and intrachain π-π overlap is credited for the observed hole mobilites as high as 0.1 cm 2 V -1 s -1 measured in FETs 11 and for the enhanced visible light absorption properties of the polymer. 12 Polythiophene analogues that exhibit higher levels of crystallinity and higher hole mobilites than P3HT, such as the regiosymmetric polymers poly(3,3-didodecylquaterthiophene) (PQT-DD) 13,14 and poly(2,5-bis(3-tetradcylthiophen-2-yl)thieno[3,2b]thiophene) (PBTTT), 15 have been studied for use in FETs, displaying mobilities from 0.18 to 0.6 cm 2 V -1 s -1 . Such polymers achieve a greater overall degree of crystallinity than P3HT based on the length and distribution of alkyl side chains, which favors long-range three-dimensional ordering via π-π stacking and side-chain interdigitation. While such polymers define the state-of-the-art in solution-processed FETs, their photovoltaic performance has not yet been reported, so it is unclear whether the enhanced inherent crystallinity will be beneficial to composite solar cells. As a means of investigating such highly ordered polymers and directly assessing the influence of a high degree of crystallinity on solar cell performance, here we examine two thiophene-alkylthiophene copolymers with identical molecular weight, composition, and electronic structure, which are composed of equal parts of 3-dodecylthiophene and unsubstituted thiophene. The first polymer is the perfectly alternating copolymer PQT-DD, described above, and the other is the random copolymer poly(3-dodecylthiophene-co-thiophene) (P3DDT-co-T). The effect of substituent sequence distribution on polymer crystallinity and solar cell performance in PCBM based BHJ devices is examined.

Organic small molecule semiconductors have many advantages over their polymer analogues. However, to fabricate organic semiconductor-based devices using solution processing, it is requisite to eliminate dewetting to ensure film uniformity and desirable to assemble nanoscopic features with tailored macroscopic alignment without compromising their electronic properties. To this end, we present a modular supramolecular approach. A quaterthiophene organic semiconductor is attached to the side chains of poly(4-vinylpyridine) via noncovalent hydrogen bonds to form supramolecular assemblies that act as p-type semiconductors in field-effect transistors. In thin films, the quaterthiophenes can be readily assembled into microdomains, tens of nanometers in size, oriented normal to the surface. The supramolecules exhibited the same field-effect mobilities as that of the quaterthiophene alone (10−4 cm2/(V·s)). Since the organic semiconductors can be readily substituted, this modular supramolecular approach is a viable method for the fabrication of functional, nanostructured organic semiconductor films using solution processing.

We report the synthesis and characterization of boron(subphthalocyanine) derivatives with bithiophene and quaterthiophene as axial ligands, i.e., thiophene−subphthalocyanine dyads (nT-SubPcs), and their application in organic photovoltaic cells (OPVs). Thin films of nT-SubPcs prepared via solution processing can act as the electron donor in bilayer OPVs with evaporated C60 as the electron acceptor. The photophyscial and morphological properties of the nT-SubPcs are studied to rationalize OPV device parameters. The single-crystal X-ray structure is solved for two dyads to show the molecular structures in the solid state, and UV−vis spectroscopy and fluorescence spectroscopy are used to characterize the effect of conjugated thiophene ligands on the photophysical properties, i.e., absorption and photoluminescence quantum yield. Cyclic voltammetry, density functional theory (DFT) calculations, and low-temperature photoluminescence spectra show that photoluminescence yields depend on the overall flexibility of the SubPc derivatives and not on the oxidation potential or electronic relationship of the ligand and macrocycle molecular orbitals. We show with grazing-incidence X-ray scattering and atomic force microscopy (AFM) that careful choice of ligand structure can improve the crystallinity of thin films that leads to a relative increase in short-circuit current in OPV device. Our work clearly demonstrates that SubPcs can be used as light-harvesting chromophores in a matrix of a crystalline organic semiconductor for OPVs.