Effect of Dimensionality in Dendrimeric and Polymeric Fluorescent Materials for Detecting Explosives

Steady-state Stern-Volmer analysis is uniformly used to assess in solution the efficiency of a sensing molecule for a particular analyte We use a combination of steady state Stern-Volmer analysis and time resolved photoluminescence (TRPL) to determine the underlying mechanisms by which fluorescent sensing materials comprised of fluorene based chromophores sense nitro-based explosive analytes The ability of two first-generation dendrimers comprised of bifluorene-containing chromophores to sense explosive analytes was compared with the chemically related polymer poly(9,9-di-n-octylfluoren-2,7 diyl) One dendrimer was planar with a single chromophore with the second having four chromophores tetrahedrally arranged around an adamantyl center All the materials had high photoluminescence quantum yields of around 90% and were able to sense explosive analytes via quenching of their fluorescence The three-dimensional dendrimer based upon the adamantyl core was found to have the highest Stern-Volmer constants for all the analytes tested with the planar dendrimer also proving to be on average superior to the polymer The TRPL measurements showed that sensing occurred by a combination of collisional and static quenching with the proportion of collisional quenching being based on the number of aromatic units in the analyte Steady-state fluorescence polarization anisotropy measurements of the three materials revealed that for the three-dimensional dendrimer an exciton can migrate between all of the chromophores, meaning that an exciton formed on one chromophore of the dendrimer can be quenched by an analyte interacting with a second chromophore This gives rise to the potential for sensing response amplification and explains its superior performance to the planar dendrimer and polymer