Solution Processable Organic Field-Effect Transistors Utilizing an α,α‘-Dihexylpentathiophene-Based Swivel Cruciform

Thiophene-Based Organic Semiconductors

Thiophene-based π-conjugated organic small molecules and polymers are the research subject of significant current interest owing to their potential use as organic semiconductors in material chemistry. Despite simple and similar molecular structures, the hitherto reported properties of thiophene-based organic semiconductors are rather diverse. Design of high performance organic semiconducting materials requires a thorough understanding of inter- and intra-molecular interactions, solid-state packing, and the influence of both factors on the charge carrier transport. In this chapter, thiophene-based organic semiconductors, which are classified in terms of their chemical structures and their structure-property relationships, are addressed for the potential applications as organic photovoltaics (OPVs), organic field-effect transistors (OFETs) and organic light emitting diodes (OLEDs).

A cyclic octithiophene containing β,β'-linkages

A cyclic octithiophene containing two β,β'-linkages was synthesized. Due to the large structural change in the excited state, this compound exhibited bathochromically shifted fluorescence. It also showed a small difference between the first and second oxidation potentials, indicative of spin delocalization through the β,β'-linkage in the one electron-oxidized state.

One pot synthesis of tetrasubstituted thiophenes: [3 + 2] annulation strategy

A simple, efficient and economical synthesis of dimethyl 3-amino-5-(2-oxo-2-arylethyl)thiophene-2,4-dicarboxylates has been reported by ring opening of methyl 3-amino-6-aryl-4-oxo-4H-thieno[3,2-c]pyran-2-carboxylates by alkoxide ions.

Synthesis and structure–property investigation of multi-arm oligothiophenes

A series of soluble 3D-oligothiophenes with different conjugation lengths are synthesized and characterized. Physical properties and formation of charge transfer complexes of oligothiophenes with Hg(ii) ions and TCNQ are investigated.

Synthesis and photophysical properties of pyrene-based green fluorescent dyes: butterfly-shaped architectures

A few pyrene-based fluorescent compounds were synthesized using Pd/Cu-catalyzed cross-coupling reaction. Photophysical properties of the π-conjugated pyrene derivatives were studied and the results indicate materials with high quantum efficiency and high extinction coefficient. No π stacking was observed in the crystal lattice. The molecules described here may be useful in developing sensors or imaging agents.

Benzobisoxazole cruciforms as fluorescent sensors

CONSPECTUS: Cross-conjugated molecular cruciforms are intriguing platforms for optoelectronic applications. Their two intersecting π-conjugated arms allow independent modulation of the molecules' HOMO and LUMO levels and guarantee a well-defined optical response to analyte binding. In addition, the rigid cross-conjugated geometries of these molecules allow their organization in two- and three-dimensional space with long-range order, making them convenient precursors for the transition from solution-based to the more practical solid-state- and surface-based devices. Not surprisingly, a number of molecular cruciform classes have been explored because of these appealing properties. These include tetrakis(arylethynyl)benzenes, tetrastyrylbenzenes, distyrylbis(arylethynyl)benzenes, tetraalkynylethenes, biphenyl-based "swivel" cruciforms, and benzobisoxazole-based cruciforms. In this Account, we summarize our group's work on benzobisoxazole molecular cruciforms. The heterocyclic central core of these molecules forces their HOMOs to localize along the vertical bisethynylbenzene axis; the HOMO localization switches to the horizontal benzobisoxazole axis only in cases when that axis bears electron-rich 4-(N,N-dimethylamino)phenyl substituents and the vertical axis does not. In contrast, the LUMOs are generally delocalized across the entire molecule, and their localization occurs only in cruciforms with donor-acceptor substitution. Such spatially isolated frontier molecular orbitals (FMOs) of the benzobisoxazole cruciforms make their response to protonation very predictable. Benzobisoxazole cruciforms are highly solvatochromic, and their fluorescence quantum yields reach 80% in nonpolar solvents. Solutions of cruciforms in different solvents change emission colors upon addition of carboxylic and boronic acid analytes. These changes are highly sensitive to the analyte structure, and the emission color responses permit qualitative discrimination among structurally closely related species. In self-assembled complexes with boronic acids, benzobisoxazole fluorophores switch their analyte preferences and become responsive to Lewis basic species: phenoxides, amines, ureas, and small organic and inorganic anions. These sensing complexes allow the decoupling of the sensor's two functions: a nonfluorescent boronic acid does the chemistry through the exchange of its labile B-O bonds for other nucleophiles, and it can be optimized for solubility and analyte specificity; the benzobisoxazole fluorophore senses the electronic changes on the boron and reports them to the operator through changes in its emission colors, allowing this sensing element to be kept constant across a broad range of analytes. We have recently expanded our studies to benzimidazole-based "half-cruciforms", which are L-shaped rigid fluorophores that maintain most of the spatial separation of FMOs observed in benzobisoxazole cruciforms. Unlike benzobisoxazoles, benzimidazoles are acidic on account of their polar N-H bonds, and this feature allows them to respond to a broader range of pH values than their benzobisoxazole counterparts. The deprotonated benzimidazolate anions maintain their fluorescence, which makes them promising candidates for incorporation into solid-state sensing materials known as zeolithic imidazolate frameworks.

Monodisperse Low-Bandgap Macromolecule-Based 5,5'-Bibenzo[c][1,2,5]thiadiazole Swivel Cruciform for Organic Solar Cells

A novel low bandgap star-like macromolecule was synthesized and applied as electron donor material in the bulk heterojunction solar cells, in which the 5,5'-bibenzo[c][1,2,5]thiadiazole was used as the central node, in conjunction with four conjugated donor-acceptor arms. Compared with the corresponding small molecule with first generation arms, the macromolecule with second generation branches exhibited significantly enhanced photovoltaic device performances (blended with PC71BM as the active layer) due to dramatically improved short-circuit current density (J_sc) and fill factor (FF). The improvement in J_sc and FF can be attributed to the more broad absorption and the more favorable phase separation when comparing a monodisperse macromolecule with the second generation arms (SFTBT) with a small molecule with first generation branches (DFTBT).

Benzo[1,2-b:4,5-b']dithiophene-based cruciforms: syntheses, crystal structures, and charge transport properties

Cruciform compound, 2,6-bis(phenylethynyl)-4,8-bis(phenylethynyl)benzo[1,2-b:4,5-b']dithiophene and its alkyl substituted derivatives, 1a-d, were designed and synthesized. Their physicochemical properties were studied by thermogravimetric analysis, absorption spectra, and cyclic voltammetry. Single crystal diffraction results revealed that 1a-d adopted different molecular packing in the solid state, which was caused by the introduction and the different orientations of alkyl chains. The single micrometer ribbon transistors of 1a displayed high mobility up to 0.81 cm(2) V(-1) s(-1). And the as-spun thin film transistors of 1c exhibited mobility as high as 0.106 cm(2) V(-1) s(-1), 2 orders of magnitude higher than those of 1b (0.006 cm(2) V(-1) s(-1)) and 1d (0.002 cm(2) V(-1) s(-1)).