An aggregation-induced emission-active bis-heteroleptic ruthenium(ii) complex of thiophenyl substituted phenanthroline for the selective “turn-off” detection of picric acid

Abstract

The development of metal complex-based aggregation-induced emission (AIE) active materials is of great importance and a challenging task. We have designed and successfully synthesized a new bis-heteroleptic ruthenium(II) polypyridine complex, Ru-1, of a thiophenol substituted 1,10-phenanthroline based ligand (L1). The solution structure of Ru-1 was fully characterized by 1D (¹H, ¹³C) and 2D (¹H-¹H COSY, ¹H-¹³C HSQC, and ¹H-¹³C HMBC) NMR spectroscopy, and ESI-MS. Ru-1 shows aggregation-induced emission (AIE) enhancement in water and highly dense polyethylene glycol (PEG) media supported by DLS, SEM, and TEM studies. The complex, Ru-1, is weakly luminescent in acetonitrile, and a very bright luminescence of Ru-1 in the weakly soluble water and highly dense PEG media arises due to the formation of nanoaggregates and the restricted intramolecular motion (RIM). The probe in aqueous acetonitrile solution (7 : 3; v/v) is able to selectively and sensitively detect picric acid (PA) over other competitive nitroaromatic compounds through luminescence quenching. The limit of detection (LOD) signifies that Ru-1 is capable of detecting picric acid at the micromolar level. Theoretical calculations were carried out to assign electronic transitions in Ru-1, both the ground and excited states. Furthermore, a paper strip kit with Ru-1 has been constructed for the practical application and in-field detection of picric acid without any interference of other nitroaromatic analytes.