Importance of the donor unit on fluoranthene for selective detection of nitro aromatic explosives

In this work, two aggregation-induced emission enhancement (AIEE) materials encompassing phenyl (M1) and thiophene (T1) units flanked to fluoranthene were synthesized. We report a new packing polymorphic phase of M1 and the molecular interactions in the crystal lattice were stabilized by C[sbnd]H···π (2.882 Å) interactions. Single crystal X-ray diffraction (SXRD) studies revealed that high torsional angles of phenyl/thiophene unit on the fluoranthene endow weak π-π intermolecular interactions in the crystal lattice. The photophysical properties of M1 and T1 were explored in solution, solid-state and their AIEE phenomenon was studied in THF/water systems. Both the compounds show strong sky-blue emission at 453 nm (M1) and 460 nm (T1). The fluorescence lifetime and quantum yields are varied significantly in the aggregated form. The emission enhancement ascribed due to restricted intramolecular rotation (RIR) of thiophene/phenyl with central π-conjugated fluoranthene in the aggregation state. Distinct changes in the surface morphology, variation in the photophysical properties and energy levels by varying the THF/water ratios furnish its potential towards trace detection of different nitroaromatics. Both materials show high sensitivity and selectivity towards detection of Trinitrophenol (TNP), however, T1 showed a high quenching rate constant at f_w = 90 % (K_SV = 5.81 × 10⁴ M⁻¹) with LOD of 0.6 ppm at f_w = 70 %. The observed fluorescence quenching is attributed due to photoinduced electron transfer from fluoranthene to nitroaromatics through static quenching process. The remarkable efficiency of these fluorescent probes were further explored towards the analysis of river/tap water samples, suggesting their high potential for use in field analysis.