Sensing nitroaromatic analytes with a bifluorene-cored dendrimer

A first generation dendrimer comprised of a 9,9,9',9'-tetra-n-hexyl substituted 2,2'-bifluorene core, biphenyl dendrons, and 2-ethylhexyloxy surface groups can rapidly detect high electron affinity, explosive-related analytes such as pnitrotoluene and 2,4-dinitrotoluene. Stern-Volmer analysis of the dendrimer in solution showed that the quenching could be either collisional or static but not a combination of the two mechanisms. The Stern-Volmer analysis was found to be critically dependent on correcting for the absorption of the analyte at the excitation wavelength and the inner filter effect. Films of the dendrimer were found to have a measurable decrease in the PL for all the nitroaromatic analytes in seconds. The luminescence of the films could be recovered on removal of the analyte. It was found that both thin (25 nm) and thick (80 nm) films showed a rapid response to the analytes but for the less volatile analytes the final level of quenching was less for the thicker films.