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A combination of analytical techniques has proved its worth in assessing a series of non-linear optical materials for use in future organic optoelectronics devices. Juan López Navarrete of the University of Malaga, Spain, and colleagues at the University of Zaragoza-CSIC and the University of Minnesota, Morris, USA, used UV-vis, IR, and Raman spectroscopy, nonlinear optical (NLO) measurements, X-ray diffraction, and cyclic voltammetry to assess the properties of a series of tricyanovinyl (TCV)-substituted oligothiophenes. The researchers explain how linear pi-conjugated oligomers, such as the oligothiophenes, have been of interest because of their intriguing optical, electrical, and photoelectrical properties for several years. Indeed, these molecules have already found application in organic semiconductor devices, as emitters and photovoltaic cells in photonics. Their "rich" non-linear optical characteristics have also led to the construction of electrooptical devices. The benefit of going organic with such devices is that these molecules are much more amenable to processing and property fine-tuning compared with inorganic materials. Some oligothiophenes can undergo intramolecular charge transfer by design, López Navarrete adds, but variations on the theme that are symmetric and can absorb two photons have not been investigated so closely. The researchers point out that such materials could be used in two-photon excited fluorescence microscopy, optical limiting, and in three-dimensional optical data storage. Additionally, such an absorption characteristic could be combined in the same molecule with electrical conductivity. As such, the team has designed and synthesised a series of TCV-substituted oligothiophenes and demonstrated just such behaviour using a raft of techniques. The team has correlated the precise behaviour with the substitution pattern of the molecules. Specifically, the team looked at the intramolecular pi-donor and pi-acceptor interactions and how these change depending on the substitution pattern. UV/Vis absorption, IR and Raman spectroscopy provided key information that can influence the electrooptical applications for such molecules. The team was also able to support the combined experimental analytical results with density functional theory. Related links:
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Orbital topology causing NLO |
