DOI: 10.1002/chem.200900702 Synthesis, Spectroscopy, Nonlinear Optics, and Theoretical Investigations of Thienylethynyl Octopoles with a Tunable Core María Moreno Oliva, [a] Juan Casado,* [a] Juan T. López Navarrete,* [a] Gunther Hennrich,* [b] Stijn van Cleuvenbergen, [c] Inge Asselberghs, [c] Koen Clays, [c] M. Carmen Ruiz Delgado, [d] Jean-Luc BrØdas, [d] J. SØrgio Seixas de Melo, [e] and Luisa De Cola [f] Introduction The synthesis of extended p-conjugated systems has been the key to providing organic materials with electro-optical properties needed for particular applications. [1] Over the past few years, numerous synthetic routes have been investi- gated to optimize the molecular hyperpolarizabilities in oc- topolar molecules for nonlinear optical (NLO) response [2] and, more recently, two-photon absorption (TPA) proper- ties. [3] Many of these organic systems present C 3 -symmetric architectures in which a central core is trigonally substituted with conjugated branches in between donor–acceptor groups and conjugative interactions with the center have been established. These types of dyes are also examples of molecules with p-electron delocalization extending in two dimensions (2D), which were recently successfully exploited as semiconductor elements in organic field-effect transistors and in light-emitting diodes. [4] It is clear that the design of these molecules, or improved derivatives, must be founded on comprehensive knowledge of their electronic characteris- tics, in particular, their ground- and excited-state properties. For instance, it has been shown that donor–acceptor Abstract: We have synthesized three new molecules that have three thienACHTUNGTRENNUNGyl- ACHTUNGTRENNUNGethynyl arms substituting a central ben- zene core and different electron donor/ acceptor groups in the three remaining phenyl positions. The absorption, fluo- rescence, phosphorescence, and transi- ent triplet–triplet spectra are analyzed in the light of the electronic structure of the ground and excited states ob- tained from quantum-chemical calcula- tions. From the above, the relevant photophysical data (including quantum yields, lifetimes, and rate constants) could be derived. It was found that the major deactivation pathway is internal conversion, which competes with the fluorescence and intersystem crossing processes. For the three investigated compounds, we provide convincing the- oretical support corroborating these findings and further conclusions based on the theoretical information ob- tained. These molecules are one of the very few cases in which the depolariza- tion ratios, obtained from the NLO op- tical measurements, clearly reflect the octopolar configuration. Molecular hy- perpolarizabilities have been measured and display a typical dependence on the donor–acceptor substitution pat- tern. Keywords: density functional calcu- lations · donor–acceptor systems · nonlinear optics · phosphorescence · sulfur heterocycles [a] M. M. Oliva, Dr. J. Casado, Prof. J. T. López Navarrete Department of Physical Chemistry, University of Mµlaga Campus de Teatinos s/n, Mµlaga 29071 (Spain) E-mail : casado@uma.es [b] Dr. G. Hennrich Departamento de Química Orgµnica Universidad Autónoma de Madrid Cantoblanco, Madrid 28049 (Spain) E-mail : teodomiro@uma.es [c] Dr. S. van Cleuvenbergen, Dr. I. Asselberghs, Dr. K. Clays Department of Chemistry, Katholieke Universiteit Leuven Celestijnenlaan 200D and F, B-3001 Leuven (Belgium) [d] Dr. M. C. Ruiz Delgado, Prof. J.-L. BrØdas School of Chemistry and Biochemistry and Center for Organic Pho- tonics and Electronics, Georgia Institute of Technology Atlanta, Georgia 30332-0400 (USA). [e] Prof. J. S. Seixas de Melo Department of Chemistry University of Coimbra, 3004-535 Coimbra (Portugal) [f] Prof. L. De Cola Physikalisches Institut, Westfälische Wilhelms-Universität Münster Mendelstrasse 7, 48149 Münster (Germany) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200900702. Chem. Eur. J. 2009, 15, 8223 – 8234  2009 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 8223 FULL PAPER