Synthesis, Characterisation and Optical Properties of Silica Nanoparticles Coated with Anthracene Fluorophore and Thiourea Hydrogen‐Bonding Subunits

Abstract

AbstractBifunctionalised hybrid silica nanoparticles have been synthesised and characterised, and their optical emission properties in the presence of certain anions in acetonitrile solutions have been studied. The alkoxysilane derivatives N‐butyl‐N′‐[3‐(trimethoxysilyl)propyl]thiourea (1), N‐phenyl‐N′‐[3‐(trimethoxysilyl)propyl]thiourea (2) and 3‐[(anthracen‐10‐yl)methylthio]propyltriethoxysilane (3) were prepared and used to functionalise uncoated LUDOX silica nanoparticles with a mean diameter of 18 ± 2 nm. The functionalisation of the nanoparticle surfaces was carried out by two different approaches. The first approach relies on the consecutive grafting of the two subunits. In this protocol, the nanoparticles were first functionalised with anthracene derivative 3 (solid NA), and then treated with the corresponding binding sites 1 or 2 to result in the NA‐Pt3 and NA‐Bt3 solids. The second approach deals with the simultaneous grafting of 1 or 2 and the signalling subunit 3 in different ratios. This method was used for the preparation of the NA1Pt1, NA1Bt1, NA1Pt3 and NA1Bt3 nanoparticles. The bifunctionalised silica nanoparticles were characterised by using standard techniques. Acetonitrile suspensions of NA nanoparticles (5 mg in 20 mL) showed anthracene bands centred at ca. 350, 370 and 390 nm. Upon excitation at 365 nm, a typical emission band with fine structure in the 390–450 nm range was observed. Similar absorption and emission spectra were found for the bifunctionalised nanoparticles. The work is completed with a prospective study of the fluorescence of the prepared nanoparticles in the presence of organic (acetate, benzoate) and inorganic (F–, Cl–, Br–, CN–, HSO4– and H2PO4–) anions. The apparent binding constants (adsorption constants) for the interaction of NA‐Pt3 with anions in acetonitrile were determined by performing a Langmuir‐type analysis of fluorescence titration data.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)