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

Abstract

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.

Diffusion of nitroaromatic vapours into fluorescent dendrimer films for explosives detection

“…More recently, fluorescent dendrimers have shown substantial potential as explosive sensing materials [12][13][14][15][16][17][18] owing to their high photoluminescence quantum yields, monodispersity and the ability to control and tailor the physical properties through tuning of the chemical structure. For the photoluminescence (PL) to be quenched, the fluorophore and the quencher have to be close enough to allow electron transfer to occur.…”

Exploitation of Guest Accessible Aliphatic Amine Functionality of a Metal–Organic Framework for Selective Detection of 2,4,6-Trinitrophenol (TNP) in Water

“…2,24 On the flipside, fluorescent probe based method harnessed from photoluminescence (PL)-based chemosensors possess unparalleled sensitivity, selectivity, low instrumentation cost, portability, short response time, and dual compatibility in solid and solution media. 5,[30][31][32] Several luminescent probes have been explored as fluorescence based explosive-sensors till date, 12,22,[33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] but their multi-step processing, toxicity and lack of control over molecular organization limits their wide use. 8,51 In fact, literature reports on fluorophore probe-based explosive sensing in water have been indeed scarce.…”

Assessing the sensing limits of fluorescent dendrimer thin films for the detection of explosive vapors

“…Crucially they all have sufficiently high electron affinities to quench the PL although they differ significantly in terms of their vapor pressures. [9] Figure 2a shows the PL of G1 films over time as a series of 20 second pulses of analyte vapor are delivered. The traces have been offset so that their form can be compared.…”

“…[8][9][10] However, the relevance of solution-based characterization towards solid-state detection is questionable, [10] given that the manner in which the analytes and chromophores interact with each other is different in the two phases. Given that any real-world application of this technology will likely be based upon solid-state sensing media, it is therefore essential that the performance of any potential sensing material be evaluated in the solid-state with appropriate analytes and at vapor concentrations that are below the level of a saturated atmosphere to reflect the fact that in the real world explosives are likely to be concealed or encased, which will inhibit accumulation of vapors.…”