Fabrication of self-assembled monolayer based on phenylethynylbenzene and fluorescent probe pyrene and detecting for nitroanilines

Self-Assembled monolayers (SAMs), a new type of organic ultra-thin films, show a lot of interesting properties in chemistry, physics, optics and electronic transport, and have potential application in biomaterials, nanoelectro-mechanical systems, sensors, and so on. In this paper, a full-conjugated unit-containing SAM ended with a functional amino group (NH₂) was fabricated by self-assembly and using a light-sensitive diazonium-containing compound 4-(4-amino phenylene ethynyl) benzenic diazonium salt (APEB-N₂⁺). The APEB-N₂⁺ was easily deposited on a pre-treated quartz substrate with negative charges by electrostatic interaction and then grafted on the surface of a quartz substrate through covalent bond after the decomposition of diazonium group under UV irradiation, and a stable SAM based on phenylethynylbenzene was obtained. Furthermore, based on the reactivity of the functional group NH₂, the fluorescent probe pyrene is anchored on the surface of the full-conjugated SAM through two approaches: amidation reaction between amino group on the SAM and carboxyl group of 1-pyrenebutyric acid, and self-assembly of N₂⁺, which is transferred from NH₂ on SAM, and electronegative COO-of 1-pyrenebutyric acid in basic aqueous solution. The obtained ultra-thin films with fluorescence probe pyrene exhibit luminescent property because of the emission of excimer of pyrene chromophore, which is mainly due to the formation of the g-g conformation of pyrene for the induction effect of the full-conjugated SAM. The electron-acceptor nitroanilines (NAs) can quench the fluorescence of the obtained ultra-thin film because of electron and energy transfer between the electron-rich pyrene and NAs. The fluorescence quenching varies obviously for the different isomers of NA, and the quenching efficiency decreases according to the sequence of p-NA, o-NA, m-NA, because the electronic effect varies obviously when the relative position of electron withdrawing group NO₂ and donating group NH₂ of NA are different. The fluorescence of the ultra-thin film decreases with the increasing of the NA concentration.