Synthesis of a conjugated molecular triad based on 9,9-dioctyl-9H-fluorene for fluorescence sensing to determine mesotrione

A conjugated molecular triad based on pyrene and 9,9-dioctyl-9H-fluorene has been successfully synthesised via the Suzuki cross-coupling reaction with yield of 48%. In this polymerization, the Pd(PPh3)4 has been used as the catalytic in the presence of K2CO3 as base in a mixture of toluene/ethanol/H2O at 80oC under N2. The chemical structures of the conjugated molecules were determined via Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H-NMR) that proved the chemical structure of 1,1’-(9,9-dioctyl-9H-fluorene-2,7-diyl)dipyrene. The optical properties of the molecules were investigated via UV-Vis in different concentration that exhibited the maximum absorption of 340 nm. The conjugated molecular triad also have been investigated by fluorescence spectroscopy that showed a mission peak at 475 nm under the excitation of 350 nm of wavelength. In addition, the 1,1’-(9,9-dioctyl-9H-fluorene-2,7-diyl)dipyrene exhibited a fluorescence quenching as a chemosensor in the presence of mesotrione, a nitroaromatic herbicide. This phenomenon proved the efficient energy and electron transfer from a photo-excited pyrene moiety to the ground state electron-deficient mesotrione as a result of Forster resonance energy transfer (FRET) mechanism.