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Fourier transform infrared and Raman spectra of a novel series of neutral α, ω-bis(mesitylthio)oligothiophenes and some α,ω-bis(mesitylthio)oligothiophenes containing ethylenedioxy groups at the β positions, with various chain lengths have been investigated. Because these compounds contain carbon-sulfur linkages they can be viewed as models for prototypical surface-bound molecular wires in which the oligomer is linked to the surface by a thiol-metal bond. Thus, interactions between the conjugated moiety and the metallic surface or cluster can be simulated. These studies are very important in order to apply molecular systems in micro and optoelectronic devices. The statements of effective conjugation coordinate theory and density functional theory calculations let us describe the specific electronic interactions between the mesitylthio groups and the oligothiophene backbone. An increased π-electron delocalization or conjugation length with respect to the α,ω-bis(alkyl)oligothiophenes of the same length has been noticed. The inclusion of C-S bridges between the end groups and the central π-conjugated backbone increases the π-electron delocalization within the oligomeric chain and precludes the oligothiophene moiety from conjugative interactions with the mesityl rings. [ABSTRACT FROM AUTHOR]

The degree of π conjugation in a novel series of molecular materials containing a central oligothiophene moiety of variable length, with its end α positions capped by phenyl groups (PnTP; n = 1-4) is closely inspected by means of Fourier-transform infrared and Fourier-transform Raman spectroscopies in the neutral state as solids. Density functional theory quantum chemical calculations were performed for each co-oligomer, at the B3LYP/6-31G[sup **] level, to obtain the optimized molecular geometry and force field. The thermal stability of these oligothiophenes has been also investigated, at the molecular level, by recording infrared and Raman spectra at different temperatures between - 170 °C and 160°C. [ABSTRACT FROM AUTHOR]

Three crystalline N-trialkyltriindoles in which the length of the alkyl chains attached to the nitrogen has been enlarged from a methyl to a butyl and to a hexyl group have been investigated in the search for semiconducting triindole easy to process from solution. We have found that the number of carbon atoms of the N-alkyl chains has a significant impact on how these molecules interact with each other in the bulk materials and it strongly influences the final morphology of the crystals, which grow as long crystalline wires, cubes or microbelts. Single crystal analysis allows us to recognize the contribution of several cooperative CH–π interactions to guide the self-assembly of these types of molecules. In addition, alkyl chain engineering allows triindole derivatives processable for solution, which render OFETs showing field effect mobilities of 0.03 cm2 V−1 s−1 and 6 × 10−3 cm2 V−1 s−1 when vapor deposited and drop casted, respectively. The results of this study represent a step forward towards the rational control of the supramolecular arrangement of this high performance semiconducting platform, this being a key fact for designing efficient solution-processed organic semiconductors. [ABSTRACT FROM AUTHOR]