PHENYLETHYNYLENE CALIX[4]ARENES AS FLUORESCENCE SENSORS FOR NITROAROMATIC COMPOUNDS

Abstract

This research deals with two novel fluorescent sensor series: the first series are calix[4]arene derivatives for TNT detection (part A) and the second series are salicylidenehydrazides for Al3+ detection (part B). In part A, the upper-rim of calix[4]arene is modified with phenylacetylene derivatives via Sonogashira coupling reaction to produce a wider cavity for entrapping TNT, which is highly explosives and recognized as a toxic substance. To improve water solubility, hydrophilic groups such as carboxyl, hydroxyl and amino groups were placed on the modified wider rim (BAC, SAC and ANC). The modified calix[4]arene with amino groups on the wider rim (ANC) exhibits highly selective fluorescence quenching toward TNT compared to the other nitro aromatic compounds in an aqueous medium due to the shape and hydrophobicity of the modified cavity. In addition, the electron donating amino groups on the phenyl ring on ANC enhances the sensitivity toward TNT comparing with BAC and SAC. The Stern-Volmer fluorescence quenching constant of TNT is 1.09 x 105 M-1 with limit of detection limit of 0.3 µM. The paper-based sensor ANC was also fabricated for a visual on-site detection of trace residues of TNT and its vapor. Part B, a series of N-salicylidenehydrazide derivatives has been developed for selective turn-on detection of Al3+ cation in aqueous media with large stroke shifts with three emissive colors, attributing to chelation-enhanced fluorescence (CHEF) effects which inhibit the non-radiative PET and ESIPT processes. Furan-2-carbohydrazide (F2) was chosen as a core structure for further design in shifting the blue emission to a longer wavelength. The addition of the second hydroxyl group at the para-position of a phenol (F3) and the additional of second hydrazide group on the phenol ring (F4) resulted in tuning the emission to longer wavelengths and also enhancing the ligand interaction with Al3+ cation. The developed F4-Al3+ complex integrates many attractive features into a single probe molecule, which includes emission at long wavelength (601 nm), remarkably large stroke shifts (133 nm) with the low detection limit of 3.1 nM. This thesis research was successful in design and synthesis the two novel fluorescent sensor series for selective detection of TNT (series 1) and Al3+ ion (series 2).