Formation and nonlinear optical properties of Ag nanocrystals capped with the conjugated ligand carbazolyl styryl terpyridine

Abstract

The third-order nonlinear materials have been the focus of present research. It is known that the w (3) value of the organic optical material is generally small, and hardly displays any evident third order nonlinear effect.However, the w (3) value was significantly improved when the organic ligands were combined with nano-Ag due to the increase of surface plasmon resonance. The nano-Ag changes its local electric field, and in turn causes a regional interaction between the ligand and the metal clusters. In this article, a new optical carbazole derivative (E)-2-(4-([2,2 0 :6 0 ,2 00 -terpyridine]-4 0 -yl)styryl)-9-hexyl-9H-carbazole, abbreviated as L, has been designed and synthesized. The ligands were combined with nano-Ag, acting on the surface and stabilizing the system without any extra control such as surfactant and pH, which may be explained by the theory of hard and soft acid-base. Careful characterizations have been performed by UV-vis absorption spectroscopy, 1 H NMR spectroscopy, FT-IR, XRD and TEM. Particular properties have been shown by fluorescence spectra, fluorescence lifetime, Raman spectrum, non-linear optical response and cyclic voltammetry curve. The results indicate that the nano-composite L-Ag NCs have a stronger Raman enhancement effect, shorter fluorescence lifetime and larger two-photon absorption (TPA) when compared to the free ligand L. The data for the TPA cross-section value (s = 1336.85 GM), nonlinear refractive index (g = 2.23 Â 10 À13 cm 2 W À1 ) and third order nonlinear optical susceptibility (Re(w (3) ) = 1.16 Â 10 À11 esu) are measured and discussed.