The four model configurational triads of poly(3-hexylthiophene) (PHT) were synthesized by cross-coupling of the appropriate stannyl and bromo 3-hexylthiophene derivatives, catalyzed by Pd[(C6H6)3P] 4.The comparison of and 13C NMR chemical shifts of the triads with those of PHT allows the unambiguous assignment of the regiochemistry of the polymer. The NMR data of the triads, in conjunction with the results of force field MMP2 calculations, also give information on the conformational properties of PHT samples of different regiochemistry.

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 SO 2 f 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,Sdioxides are reported.

Among the most appealing features of oligothiophenesÐwhich are actively investigated for a broad range of electronic applications [1±7] Ðare their chemical stability and ease of functionalization, which allows the fine tuning of relevant properties. Unsubstituted oligothiophenes are p-type, hole-transporting, semiconductor materials and one of the research objectives in the field of organic-based devices is to achieve the kind of functionalization capable of giving stable derivatives displaying n-type semiconductor properties [8±10] for the preparation of electron-transporting layers. One of the possible ways to achieve this objective is functionalization with strongly electron-withdrawing groups, which can be designed to increase the electron affinity of the material.[11]We report here a new strategy towards functionalization of oligothiophenes that consists of the chemical transformation of thienyl sulfurs into the corresponding S,S-dioxides. We show that this kind of functionalizationÐwhich implies the dearomatization of the thiophene ringsÐleads to very stable oligomers with increased electron delocalization and has also a dramatic effect on their electron affinity as deduced from their electrochemical reduction potential. It is worth mentioning that the synthesis and the characterization of unsubstituted thiophene S,S-dioxide has been reported only very recently [12] and that only S,S-dioxides derived from polysubstituted thiophene are stable at room temperature.[13±15] So far, no electrochemical data on this kind of compound have yet been published. The oligothiophene S,S-dioxides were prepared either by action of m-chloroperoxybenzoic acid (m-CPBA) on the parent oligothiophenes [16] or by assembly of the appropriate building blocks via the Stille reaction, according to the improved procedure recently described by us. [17] As an example, the synthesis of a,w-bis(dimethyl(t-butyl)silyl)-2,2¢:5¢,2²:5²,2²¢-quaterthiophene-1,1-dioxide, 5, is illustrated in Scheme 1.As shown in Table 1, which includes the main optical and electrochemical data for a series of structurally correlated tetramers and pentamers, the maximum absorption wavelength of 5 (OTTT) is red shifted by 48 nm with respect to that of the parent quaterthiophene (TTTT), indicating a greater delocalization of the electronic charge. Moreover, while the oxidation potential of OTTT only increases by 0.09 V with respect to that of TTTT, the reduction potential is shifted by 0.84 V towards less negative values, resulting in a substantial increase of the electron affinity and also a decrease of the energy gap, DE el , of OTTT with respect to that of the precursor quaterthiophene.A similar trend in the variation of the oxidation and reduction potentials evaluated by cyclic voltammetryÐfol-lowing the dearomatization of one terminal ring by formation of the corresponding S,S-dioxideÐwas observed for the entire series of oligomers from the dimer to the pentamer bearing ±SiMe 2 t Bu or ±(CH 2 ) 5 CH 3 groups at the a,w positions. This trend is shown in Figu...

Oligothiophenes in solution and in the solid state have different conformational properties, as can be concluded from the spectroscopic and theoretical data and X‐ray structure of three di‐ and tetramethyl α‐conjugated quaterthiophenes (see Figure) reported here.

The facile synthesis of poorly soluble unsubstituted and modified alpha-quinque- and sexithiophenes under microwave irradiation in the liquid phase is described. The use of microwave irradiation allowed these compounds to be prepared in a few minutes and at high yields by means of the Suzuki cross-coupling reaction. Unsubstituted sexithiophene was obtained in 10 min via the one-pot borylation/Suzuki reaction, purified according to a very simple procedure, and isolated in 84% yield. The efficient synthesis of two new methylated quinque- and sexithiophenes displaying liquid crystalline properties is reported. A new microwave-assisted methodology for the conversion of aldehyde-terminated quinque- and sexithiophenes into the corresponding cyano derivatives is also described. The use of microwaves was extended to the Sonogashira coupling reaction and found to be very effective in the preparation of a quinquethiophene containing acetylenic spacers. The electronic and optical characterization of this compound is reported and discussed in relation to that of unsubstituted quinquethiophene.