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Optical, Redox, and NLO Properties of Tricyanovinyl Oligothiophenes: Comparisons between Symmetric and Asymmetric Substitution Patterns
Author(s) -
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
Publication year - 2006
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200501389
Subject(s) - intramolecular force , molecular orbital , tetracyanoethylene , stacking , homo/lumo , density functional theory , molecule , intermolecular force , chemistry , cyclic voltammetry , oligomer , raman spectroscopy , crystallography , computational chemistry , materials science , photochemistry , electrochemistry , stereochemistry , organic chemistry , electrode , physics , optics
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).