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Thiophene-based compounds have acquired increasing importance in materials science and technology, owing to their multiple functional properties, chemical robustness, and versatility. Research studies involving thiophene-based materials are highly interdisciplinary and range from organic electronics, in which the semiconducting properties of these materials are exploited in devices such as thin film field-effect transistors and solar cells, to bioimaging, in which their optical properties are exploited to monitor biological events involving proteins and DNA. Since all fields are concerned with the synthesis of new molecular structures, this chapter also deals with the most recent advances in the synthesis of oligo- and polythiophenes.

This chapter illustrates the relationships between structural and optical properties in oligothiophenes. In particular, it highlights the proper functionalization of the thienyl units with oxygen atoms; it is possible to increase the photoluminescence efficiency up to values comparable and even better than those of the best organic materials commonly used as active compounds in light emitting devices. Such a characteristic, together with the high chemical stability and the wide color tunability, makes oligothiophene-5,5'-dioxides excellent candidates not only for applications to electronic devices, but also to optoelectronic devices, such as multi-color LEDs and lasers. Recent achievement of high-performances thiophene-based devices is discussed.

Versatile synthetic methods towards a variety of thiophene-nucleobase hybrid systems are reported. Adenine- and thymine-based modified nucleosides characterized by a bithiophene unit linked to the C5' or C8 position through an ethylenamino or an ethylensulfanyl bridge were synthesized and successfully polymerized in the presence of FeCl3. The self-organization properties of the pure polymers as well as their mixtures - with complementary nucleobases - were investigated by means of optical microscopy and AFM in cast film showing complex supramolecular structures resulting from the interplay of multiple intermolecular interactions.

We report on the fabrication of the first bicolor micropixelated OLED from a single molecular material using a single-step bottom up procedure, The implementation of a deposition technique, based on a spatial-switch and con formational-sensitive STD surface-tension-driven lithography, has allowed us to exploit the spontaneous supramolecular properties and the conformational flexibility of a conjugated thiophene-based material, 6-bis-(50-hexyl-[2, 20]bithiophen-5-yl)-3, 5-dimethyl-dithieno[3, 2-b: 20, 30-d]-thiophene (DTT7Me). The existence of two regularly alternating emitting regions on a micrometer scale allows obtaining electroluminescent emission at two different wavelengths from a single material.

We show that thin films grown by vacuum sublimation, or formed by melted powders, of semiconductor alpha-quinquethiophene (T5) exhibit a hierarchical self-affinity organization that spans scales from tens of nanometers to hundreds of micrometers. T5 organization was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), and optical microscopy. XRD showed that vacuum-evaporated T5 films were characterized by a preferred orientation of the h00 planes parallel to the glass substrate, Melting of the films followed by rapid quenching to room temperature led to the formation of micrometer-sized, single-crystal-like structures, characterized by uniaxially aligned stripes. XRD proved that the melting-quenching process enhanced molecular ordering and increased the size of domains with the molecule's long axes tilted by about 65degrees with respect to the substrate plane and piled up side-by-side along parallel columns. AFM measurements on the melt-quenched structures showed that a hierarchical architecture was built by reiteration across multiple length scales of the same recurring motif. Because of the tendency of T5 to form highly crystalline vacuum-evaporated thin films, a field-effect hole mobility comparable to state-of-the-art FET mobility of alpha-sexithiophene films was reached, without any attempt to optimize deposition conditions.

We show that thin films grown by vacuum sublimation, or formed by melted powders, of semiconductor R-quinquethiophene (T5) exhibit a hierarchical self-affinity organization that spans scales from tens of nanometers to hundreds of micrometers. T5 organization was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), and optical microscopy. XRD showed that vacuum-evaporated T5 films were characterized by a preferred orientation of the h00 planes parallel to the glass substrate. Melting of the films followed by rapid quenching to room temperature led to the formation of micrometer-sized, single-crystal-like structures, characterized by uniaxially aligned stripes. XRD proved that the meltingquenching process enhanced molecular ordering and increased the size of domains with the molecule’s long axes tilted by about 65° with respect to the substrate plane and piled up side-by-side along parallel columns. AFM measurements on the melt-quenched structures showed that a hierarchical architecture was built by reiteration across multiple length scales of the same recurring motif. Because of the tendency of T5 to form highly crystalline vacuum-evaporated thin films, a field-effect hole mobility comparable to state-of-the-art FET mobility of R-sexithiophene films was reached, without any attempt to optimize deposition conditions.

Thiophene oligomers have been studied so far mainly for their semiconductor and charge-transport properties. However, these compounds are also highly fluorescent and soluble. Solubility and fluorescence frequencies and efficiencies can be tailored by means of appropriate functionalization of the aromatic backbone. Functionalization with the isothiocyanate group (-N=C=S) allows these molecules to form covalent bonds with NH2-containing biomolecules and give rise to optically and chemically very stable fluorescent bioconjugates. Examples of photostable conjugates formed with monoclonal antibodies are reported.

The photoluminescence (PL) frequencies and quantum efficiencies of dithieno[3,2-b;2',3'-d]thiophene-4,4-dioxide (1), its 3,5-dimethyl derivative (2), and the corresponding 4-oxide (3) are reported and discussed in relation to their single-crystal X-ray structures. The peculiar packing modalities of dioxides 1 and 2, based on dimeric units originated by short S . . .O contacts between molecules related by an inversion center, cause an unusually high bathocromic shift of PL frequencies from solution to solid state. This effect is accompanied by a marked decrease in solid-state PL efficiencies (12% and 16%) compared to those in solution (75% and 77%). In monoxide 3 the loss of local symmetry inherent to the change SO2 --> SO deeply modifies the self-assembly and PL properties, and the PL efficiency in the solid state is close to that in solution. Ab initio calculations on the ground and excited states of compound 1 were performed and compared to those of a conformationally mobile counterpart. Oligomers containing dithienothiophene 2 as internal core were synthesized and found to be characterized by high PL efficiencies in the solid-state (up to 48%) as well as in solution (up to 85%). The current-voltage and luminance-voltage plots of an electroluminescent diode fabricated with one of these new rigid-core oligothiophene-S,S-dioxides are reported.

Physical Review Letters