ORIGINAL RESEARCH Electronic properties of thienylene vinylene oligomers: synthesis and theoretical study G. Neculqueo • V. Rojas Fuentes • A. Lo ´pez • R. Matute • S. O. Va ´squez • F. Martı ´nez Received: 27 October 2011 / Accepted: 14 February 2012 / Published online: 9 March 2012 Ó Springer Science+Business Media, LLC 2012 Abstract (E)-1,2-bis(2-thienyl)vinylene (TV), (E)-1,2-bis (3-octyl-2-thienyl)vinylene (TOV), (E)-1,2-bis(3-(2-ethyl- hexyl)-2-thienyl)vinylene (T2EHV), and (E)-1,2-bis-[2,2’- bithienyl] vinylene (BTV) have been synthesized by a com- bination of formylation reaction and Mc Murry dimerization. UV–Vis spectra of BTV showed the longest wavelength absorption, TOV and T2EHV showed a bathochromic shift to the red compared with TV, due to an increment of delocal- ization of the conjugated p-system as the result of the weakening of the carbon–carbon double bonds of the thienyl rings due to the substitution of one hydrogen by the alkyl group. Based on optical data, the effect of linear and branched alkyl chain and extension of conjugation length on the elec- tronic properties is discussed. 1 H, 13 C-NMR, UV–Visible, Fluorescence data are discussed and theoretical DFT and TD- DFT calculations of ground state and excited states have been also considered in the analysis and explanation of results. Keywords Thienylene vinylene Á Oligomers Á Optoelectronic Á TD-DFT Introduction In recent years the thienylene vinylene derivatives, formed from a combination of thiophene and the vinyl group, are known to have a delocalized p system, which is an important component for building electronic devices [1]. In addition, the incorporation of vinylene bonds between aromatic rings leads to an increment of the degree of co- planarity of the system and extend the conjugation length, reducing the steric hindrance in successive aromatic rings which is desirable for polymers to be used as electro- optical devices [2–5]. For instance, poly(thienylene vinyl- ene) has a lower band gap than polythiophene [6–12] and can be regarded as a suitable material for semiconductor applications because of high flatness, high conductivity, and great potential mobility. [8, 13] In this study, we compare the extension of conjugation length between thienylvinylene and bithienylvinylene and the effect of linear and branched alkyl chain on the elec- tronic properties of thienylvinylene. Roncali et al. have reported the effect of increasing number of thiophene rings bridged by vinylene units and also compare the a and b alkyl substituted thienylvinylene [5, 14]. They have con- cluded that alkyl substitution at a position at the end of thiophene rings has little or none influence on the solubility and electronic properties, whereas mono or di-substitution at the b position of the thiophene rings enhances strongly the solubility. At the same time, spectroscopic and oxida- tion potential of thienyl-vinylene oligomers show expected bathochromic shift of k max and decrease of the HOMO– LUMO gap with extension of the conjugation length. Theoretical approaches to calculate ground state and excited states properties have shown to be useful in this kind of systems and can yield interesting results on geometry aspects, localization-delocalization of the G. Neculqueo Á V. Rojas Fuentes Á A. Lo ´pez Á S. O. Va ´squez (&) Á F. Martı ´nez (&) Departamento de Ciencia de los Materiales, Facultad de Ciencias Fı ´sicas y Matema ´ticas, Universidad de Chile, Casilla, 2777 Santiago Chile, Chile e-mail: svasqueza@ing.uchile.cl F. Martı ´nez e-mail: polimart@ing.uchile.cl R. Matute Department of Chemistry and Biochemistry, University of California, Los Angeles, USA 123 Struct Chem (2012) 23:1751–1760 DOI 10.1007/s11224-012-9979-0