Optical, Redox, and NLO Properties of Tricyanovinyl Oligothiophenes: Comparisons between Symmetric and Asymmetric Substitution Patterns

• Published in: Chemistry : a European journal Vol. 12; no. 21; pp. 5458 - 5470
• Main Authors: Casado, Juan, Ruiz Delgado, M. Carmen, Rey Merchán, M. Carmen, Hernández, Víctor, López Navarrete, Juan T., Pappenfus, Ted M., Williams, Nathaniel, Stegner, William J., Johnson, Jared C., Edlund, Brett A., Janzen, Daron E., Mann, Kent R., Orduna, Jesús, Villacampa, Belén
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 17.07.2006; WILEY‐VCH Verlag; Wiley
• Subjects: Chemistry; Chemistry, Multidisciplinary; electronic structure; oligothiophenes; photonics; Physical Sciences; Science & Technology; semiconductors; DESIGN; 2-PHOTON ABSORPTION; DONOR; SUSCEPTIBILITIES; VIBRATIONAL-SPECTRA; semiconductors; HIGHLY EFFICIENT; TRANSPORT; END-CAPPED OLIGOTHIOPHENES; SPECTROSCOPY; electronic structure; THIN-FILM TRANSISTORS; oligothiophenes; photonics
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200501389

A series of tricyanovinyl (TCV)‐substituted oligothiophenes was synthesized and investigated with a number of physical methods including UV/Vis, IR, and Raman spectroscopy, nonlinear optical (NLO) measurements, X‐ray diffraction, and cyclic voltammetry. Mono‐ or disubstituted oligomers were prepared by the reaction of tetracyanoethylene with mono‐ or dilithiated oligomers. The comparative effects of the symmetric and asymmetric substitutions in the electronic and molecular properties have been addressed. These oligomers display dramatic reductions in both their optical and electrochemical band gaps in comparison with unsubstituted molecules. The analysis of the electronic properties of the molecules was assisted by density functional theory calculations, which are in excellent agreement with the experimental data. TCV substitution influences the energies of the frontier orbitals, especially with respect to the stabilization of LUMO orbitals. X‐ray structural characterization of a monosubstituted oligomer exhibits π‐stacking with favorable intermolecular interactions. NLO results agree with the role of the intramolecular charge‐transfer feature in the asymmetric samples. These results furthermore exalt the role of conformational flexibility in the disubstituted compounds and reveal an unexpected nonlinear optical activity for symmetric molecules. Regarding the electronic structure, the interpretation of the vibrational data reflects the balanced interplay between aromatic and quinoid forms, finely tuned by the chain length and substitution pattern. The electronic and structural properties are consistent with the semiconducting properties exhibited by these materials in thin film transistors (TFTs). Thiophenes in photonics: Symmetric and asymmetric tricyanovinyl oligothiophenes (the illustration) combine optical, electrochemical, and nonlinear optical activity for exploitation in organic photonics (i.e., solar cells). Their electronic structures have been monitored as a function of the molecular substitution pattern.