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 χ⁽³⁾ value of the organic optical material is generally small, and hardly displays any evident third order nonlinear effect. However, the χ⁽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′:6′,2′′-terpyridine]-4′-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, ¹H 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 (σ = 1336.85 GM), nonlinear refractive index (γ = 2.23 × 10⁻¹³ cm² W⁻¹) and third order nonlinear optical susceptibility (Re(χ⁽³⁾) = 1.16 × 10⁻¹¹ esu) are measured and discussed.