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wileyonlinelibrary.comAdv. Funct. Mater. 2011, 21, 897-910 Photovoltaic properties of DCV n T-Bu (n = 4, 5 and 6) with various lengths of the oligothiophene unit were also investigated. The V OC decreased from 1.13 V for DCV4T-Bu to 1.0 V for DCV5T-Bu and to 0.93 V for DCV6T-Bu, which is ascribed to the decrease in their IP and an increase in energy of the highest occupied molecular orbital (HOMO). On the other hand, no clear trend was observed for short-circuit current density ( J SC ) and fi ll factor ( FF ) values. The power conversion effi ciency of DCV4T-Bu was lower compared to DCV5T-Bu because of its lower J SC and FF, while the small differences in J SC and FF values between DCV5T-Bu and DCV6T-Bu do not represent a general trend. [ 34 ] One advantage of the vacuum-processable SMOSCs is that tandem cells can easily be fabricated. Very recently, by combining in a tandem device two bulk heterojunctions of C 60 in blend layers with an optimized DCV n T-derivative and a novel pigment with absorption range between 600 and 750 nm developed by BASF, respectively, a certifi ed effi ciency of 6.1% on 2 cm 2 active area [ 36 ] and shortly after a certifi ed record effi ciency of 8.3% on 1.1 cm 2 device have been released. [ 37 ] Herein, we investigate structure-property relationships in a series of DCV n Ts with conjugated chain lengths of one to six thiophene units (n = 1-6) and without solubilizing alkyl side chains, well being aware that synthesis and characterization of longer derivatives might be problematic due to low solubility. However, we expect that these oligomers may show good packing and thermal stability which might infl uence the solar cell performance. Synthesis of Dicyanovinyl-FunctionalizedOligothiophenes DCV n T Linear SynthesesSynthesis of the smaller members of the series, DCV1T-DCV3T 1-3 , were already described in literature and were prepared for non-linear optical properties. [ 38 , 39 ] Based on our experience with alkylated DCV n Ts, we fi rstly synthesized DCV1T-DCV4T 1-4 by a linear approach ( Scheme 1 ). Thus, bi-, ter-, and quaterthiophene dialdehydes 8-10 , [40][41][42][43] which were prepared by Vilsmeier-Haack formylation of the parent oligothiophenes [44][45][46] were reacted with malononitrile and ß-alanine as catalyst to form target DCV n Ts 2 and 3 (n = 2, 3) in nearly quantitative yield and in high purity. DCV1T 1 was obtained from commercially available thiophene-2,5-dicarbaldehyde 7 and malononitrile without the use of catalyst. However, due to a dramatic decrease in solubility, reaction of quaterthiophene-dialdehyde 10 resulted in an inseparable mixture of target DCV4T 4 and the singly reacted intermediate with a DCV-group at one chain end and an unreacted formyl group at the other. Convergent SynthesesDue to solubility problems of the longer homologues, only a series up to the trimer could be reliably synthesized by the usual linear synthetic approach. Thus, we developed a convergent route to DCV-capped oligothiophenes DCV3T 3 to DCV6T 6 ( Scheme 2 ). Terminal buildin...

The novel methyl-substituted dicyanovinyl-capped quinquethiophenes 1-3 led to highly efficient organic solar cells with power conversion efficiencies of 4.8-6.9%. X-ray analysis of single crystals and evaporated neat and blend films gave insights into the packing and morphological behavior of the novel compounds that rationalized their improved photovoltaic performance.

The design and synthesis of molecules that form self-assembled monolayers on substrates is fairly well understood and developed. [1][2][3] Nevertheless, the controlled hierarchical construction of hybrid multilayers [4,5] comprising molecularscale (electronic) functionalities is a major challenge, and the first systems have been demonstrated only recently. [6,7] Here, we present the direct observation of self-assembled two-dimensional (2D) crystals of a novel class of organic semiconductors [8,9] on graphite by means of scanning tunneling mi- We have studied the long-range and short-range ordering of the conjugated macrocycle C[12]T (Scheme 1) [3,8] in self-assembled 2D crystals at the solution/highly oriented pyrolytic graphite (HOPG) interface by means of in-situ STM. Physisorption occurs from a 1,2,4-trichlorobenzene solution onto the (001) face of HOPG. In Figure 1a, a representative STM image of the cyclothiophene monolayer is shown. Longrange order of closely packed macrocycles is typically found over areas larger than 1 lm. The intrinsic high symmetry of the macrocycles (C 6v ) (Scheme 1) is preserved in the C[12]T adsorbate. The hexagonal arrangement of the molecules provides a unit cell of the 2D crystal defined by the parameters a = 2.3 ± 0.05 nm, b = 2.3 ± 0.07 nm, and c = 119 ± 3°. Six rotational domains are expected due to the two possible enantiomorphic arrangements of the macrocycles for each of the three crystallographic axes of the underlying HOPG.[10] However, only three domains have been observed in our experiments, and only two of them persist after dynamical reorganization at the surface. This fact can be explained by the weak molecule-substrate interaction and by the minimization of the interfacial energy, and will be accurately described in a forthcoming paper. Moreover, in these STM images, submolecular resolution has been achieved; the conjugated p-system of the individual rings appear in bright color, corresponding to higher tunneling currents. The interior cavity and the insulating alkyl side chains give a lower tunneling current and appear darker in the images. This image contrast is well known from previous investigations on related semiconducting linear oligo-and polyalkylthiophenes. [10][11][12] The close packing of the macrocycles on the surface brings the ring-shaped p-systems together to distances as small as 0.4 nm. Semiempirical calculations on the macrocycles indicate that the energetically most-favorable geometry has an almost planar p-system with the alkyl side chains bent in the same direction, out of the thiophene plane (Fig. 1b, inset). The "spider-like" conformation of the macrocycle on the surface allows intermolecular interactions between the alkyl side chains of adjacent molecules. These van der Waals' forces are typically the driving force for the self-organization of alkylated conjugated systems.[10] The unit-cell parameters for a calculated closest packed monolayer (a = 2.28 nm, b = 2.28 nm, c = 120°) are in excellent agreement with the experimental data (vide infr...

One-dimensional linear oligo-and polythiophenes are among the most prominent organic semiconductors for applications in organic electronics owing to their outstanding optical, redox, self-organizing, and transport properties.[1] As an example, regioregular poly(3-hexylthiophene) [2] (P3HT)-based organic solar cells showed excellent performances and power conversion efficiencies.[3] More complicated molecular shapes and increased dimensionality, which have important consequences on the electronic properties, were realized in 2D-macrocyclic, [4] disk-and starlike, [5] as well as in 3D-cruciform, [6] catenated, [7] and branched dendritic [8] oligothiophenes.Conjugated dendrimers represent a new class of macromolecular materials with shape-persistent and defined, monodisperse structures.[9] Müllens giant polyphenylene dendrimers impressively demonstrated that by precise spatial arrangement of functional groups, nanoobjects with unique physical properties become available.[10] Decoration of phenylene-, [11] oligophenylene-, [12] and polyphenylene-based dendrimers [13] with oligothiophenes at the periphery resulted in a mixed type of branched structures, whereas all-thiophene dendrons and dendrimers up to a 15-and a 30-mer, respectively, were reported only recently by Advicula and co-workers.[8]The aim of our work was to develop an effective approach to larger 3D-dendritic oligothiophenes that can be further functionalized at the periphery with, for example, dyes, redoxactive, self-organizing, or biological groups and easily attached to cores with interesting geometric and electronic properties. As this type of novel semiconducting macromolecules is monodisperse, they offer the significant advantage of reproducible and unique physiochemical properties, which is particularly important for organic electronic devices.As a basic building block, trimethylsilyl (TMS)-functionalized terthiophene 1 (Figure 1), including one a-a and one branching a-b connection of the thiophene units, was used to directly allow selective reactions at the free a-position (marked with arrow) and to build up higher generational oligothiophenes. In contrast with Advinculas systems, [8] in our case the TMS groups are ideal for further transformations at the outer a-positions and can be converted to functional groups by electrophilic ipso reactions or be cleaved off to give the "pure" oligothiophenes. Thus, the first series of silylated and nonsubstituted dendritic oligothiophenes have been efficiently built up in an iterative divergent/convergent protocol. Monodisperse and highly soluble dendrons and dendrimers up to a fourth generation (G4) were obtained.Terthiophene building block 1 was synthesized by nickel-catalyzed crosscoupling of the Grignard reagent of 2-bromo-5-trimethylsilyl-thiophene and 2,3-dibromothiophene (79 % yield). Removal of the TMS group with tetrabutylammonium fluoride (TBAF) quantitatively gave branched terthiophene 2. Lithiation of 1 with n-butyllithium (nBuLi) and subsequent reaction with 2-isopropyloxy-4,4,5,5-tetrameth...

The self‐assembling properties of π‐conjugated oligo‐, poly‐, and cyclothiophenes (see Figure) have been studied with different techniques. Scanning tunneling microscopy on perfectly ordered two‐dimensional monolayers at the solution–HOPG (highly oriented pyrolytic graphite) interface has successfully been applied. The submolecular resolution achieved in the STM images provides valuable lattice and molecular information. Supported by X‐ray structure analyses of the 3D bulk material and by theoretical calculations, molecular conformations, molecule–molecule, and molecule–substrate interactions of the oligo‐, poly‐, and cyclomers have been analyzed and discussed.

Investigation of self-organization behavior of organic (semi)-conductors became very important recently, since their physical properties and performance in organic electronic devices strongly depend on ordering effects, on both molecular and nanoscale levels. [1] In this respect, bioinspired functionalization of conjugated systems might greatly enhance the diversity of electronically interesting assemblies, and potentially allow for the rational design of hierarchically ordered nanostructures.[2] Thus, from possible hybrids of conjugated backbones, the combination of oligo-or polythiophenes with biomolecules, such as nucleotides, [3] carbohydrates, [4] or peptides, [5] are interesting. Particularly, the latter appears to be attractive, because interplay between different intermolecular forces in the peptide and oligothiophene segments results in competing self-assembly motifs. Hence, very specific organization properties can be expected. Whereas thiophene-based materials typically form well-organized 2D lamellar superstructures due to van der Waals interactions of alkyl side chains, and stack into the third dimension via p-p interactions, [6] secondary structures of peptides, preferentially bsheets or a-helices, are governed by stronger and directed hydrogen-bond formation.[7] The high tendency of peptides to adopt well-defined secondary-structure motifs has been exploited recently to guide self-organization of a broad range of synthetic polymers.[8] Attention has mainly been devoted to the b-sheet motif, leading to anisotropic fibrillar or fiber-like structures. [9] However, other highly interesting assembly motifs, for example the coiled-coil motif, were exploited, resulting in distinct nanoobjects by the lateral assembly of amphiphilic a-helices. [10] We recently presented the first conjugate between a regioregularly alkylated quaterthiophene and a pentapeptide consisting of a silk-inspired sequence of alanine-glycine repeats, which is known to adopt b-sheet structures.[5a] Unexpected and novel 3D nanostructures were found, suggesting that short peptide sequences may indeed influence the nanoscale structure, and ultimately, properties of organic semiconducting materials.The versatility of this class of hybrid oligo-/polymers is certainly not exploited, considering the diversity of both the conjugated oligo-/polymer platforms and the bioorganic segments. It becomes increasingly evident that such materials will envelop by far more structural and functional space as, for example, common AB-block copolymer systems.[11]Here, we present the synthesis and self-organization behavior of a symmetrically substituted A-B-A-type bioinspired semiconductor, quaterthiophene-peptide hybrid 8 (Scheme 1b), by combining a central quaterthiophene segment (B) with two peptide-poly(ethylene oxide) bioconjugates (A).As outlined in Scheme 1, the oligothiophene segment was substituted on both sides with an amino acid sequence Gly-(ThrVal) 3 -Gly-aPhe-Gly (Scheme 1, structure 2), with Gly ¼ glycine, Val ¼ valine, Thr ¼ threonine, ...

X-ray investigations on single crystals of a series of terminally dicyanovinyl-substituted quaterthiophenes and co-evaporated blend layers with C(60) give insight into molecular packing behavior and morphology, which are crucial parameters in the field of organic electronics. Structural characteristics on various levels and length scales are correlated with the photovoltaic performance of bulk heterojunction small-molecule organic solar cells.