Head-to-Tail interlocking aromatic rings of a hydrazine functionalized Schiff base for the development of Nano-aggregates with blue emission: Structural and spectroscopic characteristics

We report the synthesis, physicochemical and morphological characterisation, supramolecular interactions and aggregation-induced blue emission of a newly developed Schiff base, 1,2-bis(phenyl(pyridin-2-yl)methylene)hydrazine (P18). The compound was synthesised through a condensation reaction between hydrazine and 2-benzoylpyridine under reflux in ethanol. The photophysical behaviour of the Schiff base was studied in both monomeric and aggregated forms. Interestingly, the molecular aggregate showed a significant blue shift with similar to 20 fold higher fluorescence intensity with lifetime, 0.99 ns in the aqueous phase than that of monomeric form, attributed to the development of J-type aggregation. The crystal structure, C-H center dot center dot center dot pi and pi...pi interactions, were enumerated to decipher the nature of aggregation. The Schiff base consisting of four aromatic rings (two pyridine and two phenyl rings) displayed a short C-H center dot center dot center dot pi and a long distant pi...pi interactions causing a head-to-tail type interlocking of aromatic rings. Energy framework analysis confirmed the predominance of dispersive forces (-192.4 kJfinol) to the cluster of molecules, thus playing a significant role in the restriction of intramolecular motion of the aromatic rings of P18. A restrain on the rotational probability of = N-N = and Ar-C- bonds leads to an enhancement of an intense fluorescence property of nano-aggregate with blue light emission in solid state. The propagation of the rectangular-shaped monomeric probe in the nano-aggregate with an average hydrodynamic size of 270(+/- 3) nm was established with field emission scanning electron microscopy, dynamic scattering light, and electron dispersive X-ray spectral analysis. (C) 2021 Elsevier B.V. All rights reserved.