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20 April 2006 An indole-based low molecular weight glass-former giving materials with high cooperative photorefractive optical gain
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Abstract
A derivative of 2-methylindole, namely 3-[2-(4-nitrophenyl)ethenyl]-1-(2-ethylhexyl)-2-metylindole (NPEMI-E) has been synthesized. Materials obtained from this molecule have been studied as thin films between two ITO layers. The study revealed that NPEMI-E collects in itself both photoconductivity and NLO characteristics. Differential Scanning Calorimetry (DSC) measurements showed the formation of stable glass films characterized by a Tg temperature lower than room temperature. Blends with the photoconductive poly-N-vinyl-2,3-dimethylindole (PVDMI) were also studied, giving again stable glass films independently of the wt.% contents of NPEMI-E. Photorefractivity measurements on both pure and blended NPEMI-E allowed to measure a value of the optical gain Γ = 627 cm-1 at an applied electric field E = 60 V/µm. This high value of Γ corresponds to a sharp maximum of the experimental trend of Γ as a function of the wt.% content of NPEMI-E. The corresponding content was wt.% = 91.5. The presence of this maximum induced us to make the hypothesis that, besides the well known reorientational contribution to the photorefractivity, a further mechanism (recently theoretically studied) is active in our blends. This mechanism arises in the interactions among the NLO polarized and polarizable moieties (cooperative effect). It can produce a rapid variation of some of the electrooptical parameters conditioning the extent of the photorefractivity. This can happen at a well defined mean intermolecular distance and hence at a well defined concentration of the NLO molecules.
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Rocco Angelone, Marco Angiuli, Francesco Ciardelli, Arturo Colligiani, Francesco Greco, Annalisa Romano, Giacomo Ruggeri, and Elpidio Tombari "An indole-based low molecular weight glass-former giving materials with high cooperative photorefractive optical gain", Proc. SPIE 6192, Organic Optoelectronics and Photonics II, 61922M (20 April 2006); https://doi.org/10.1117/12.661692
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