Structural and Optical Insights Into a Phenothiazine-derived Chalcone Synthesized via Eco-friendly Methods

Abstract

A novel chalcone containing (hetero)aromatic units was obtained by the Claisen-Schmidt condensation of phenothiazinyl-3-carbaldehyde with 4-hydroxy-acetophenone under three experimental approaches based on classical, mechanochemical and ultrasound-assisted procedures. A comparison between the experimental outcomes emphasizes shorter reaction time and lower energy usage in the case of mechanochemical and ultrasound-assisted procedures, recommending these methods as more environmentally friendly synthetic options. Moreover, the use of the sonochemical method resulted in the formation of the reaction product in crystalline state thus simplifying the purification process. The optical properties of the new chalcone were assessed by UV-vis spectroscopy. (E)-1-(4-hydroxyphenyl)-3-(10-methyl-10H-phenothiazin-3-yl)prop-2-en-1-one exhibited an intense absorption in the UV region (λ_ₘₐₓ=408 nm) and low intensity fluorescence emission in DMSO solution (λ_ₑₘ=560 nm, Stokes shift 7558 cm^-1). The X-ray diffraction on monocrystal technique which was employed to ascertain the solid-state structure of the new chalcone revealed strong O-H···O hydrogen bonds and weak dispersive van der Waals interactions such as π···π and C-H···π contacts ensuring its supramolecular architecture, crystal cohesion and stability.