Fluoranthene Based Derivatives for Detection of Trace Explosive Nitroaromatics

A series of fluoranthene derivatives
(F1–F5) varied with nature and type
of substituents were synthesized via Diels–Alder
reaction followed by in situ decarbonylation. The
solid state structures have been established
through single crystal X-ray diffraction (XRD). The presence of extended
conjugation and having two alkyloxy chains on phenyl rings induces
flexibility to orient opposite to each other and interacts with another
fluoranthene unit with weak π–π interactions and
show unique supramolecular arrangements. The envisaged photophysical
and DFT studies demonstrated that HOMO–LUMO levels were effectively
tuned by different substituents with an optical band gap from 3.44
to 3.88 eV provoked to examine as sensitive fluorescent chemosensors
for the detection of nitroaromatic compounds (NACs). The sensitivity
toward the detection of NACs was evaluated through fluorescence quenching
in solution (aqueous and non-aqueous) and solid state (vapor and contact
mode). Fluorescence studies demonstrated that electron transfer occurs
from the electron rich fluoranthene fluorophores to the electron deficient
NACs by the dominant static quenching mechanism and the quenching
process is reversible. It was found that the detection sensitivity
increases with extent of conjugation on fluoranthene unit. The contact
mode approach using thin layer silica chromatographic plates exhibits
a femtogram (1.15 fg/cm2) detection limit for trinitrotoluene
(TNT) and picric acid (PA), while the solution state fluorescence
quenching shows for PA detection at the 2–20 ppb level. The
sensing performance of fluoranthene thin films to NACs in aqueous
solution reveals that fluorophores are highly selective towards the
detection of PA. The smart performances of thin film fluorophores
with high photostability have great advantage than those of conjugated
polymers with superior sensitive detection of PA in groundwater.