Fluorescent carbazole dendrimers for the detection of explosives

Three generations of fluorescent carbazole dendrimers with spirobifluorene cores are studied as model chemosensor systems for the detection of nitroaromatic explosives via fluorescence quenching. Stern–Volmer measurements in solution with a series of nitrated analytes including the 2,4,6-trinitrotoluene (TNT) byproduct 2,4-dinitrotoluene (DNT) and the plastic explosives taggant 2,3-dimethyl-2,3-dinitrobutane (DMNB) showed an increase in affinity and hence quenching efficiency between the first and second generation dendrimers. In spite of the differences in the solution Stern–Volmer constants the solid state quenching response to the analytes was found to be independent of generation with the exception of 1,4-dinitrobenzene (DNB), where the quenching decreases with increasing generation. It was found that it was necessary to heat the films to release the analytes with the temperature required dependent on the analyte and/or dendrimer generation. These two results show that a simple solution Stern–Volmer analysis is not always sufficient for qualifying film sensing performance and that the drive to develop sensing materials with high solution Stern–Volmer constants for real applications needs to be reconsidered.