Photochromic and molecular switching behaviour of new Schiff bases containing hydantoin rings: synthesis, characterization and crystal structures

The present study reports the synthesis and structural, photophysical and electrochemical properties of five new Schiff bases containing hydantoin rings. The compounds were synthesized via condensation reactions between 3-amino-5,5′-dimethylhydantoin and five different aromatic aldehydes. All compounds were characterized using different spectroscopic and electrochemical tools as well as single crystal X-ray diffraction analysis. The photochromic and molecular switching behaviours of the switchable –CHN– groups of Schiff bases were investigated by real time UV-vis spectroscopy in DMF under long wavelength UV light at λ = 365 nm for 90 min (mostly E → Z) and dark relaxation at room temperature for 60 min (mostly Z → E) in the spectral region of 250 nm to 600 nm at equal concentrations. The electrochemical properties of the compounds were investigated on a glassy platinum electrode (Pt-) in DMF using the cyclic voltammetric (CV) technique before and after UV irradiation. The effects of functional groups on the reduction potential of the Schiff bases are discussed. Electrochemical studies showed that the reduction of –CHN groups is mostly quasi-reversible, with adsorption-controlled processes for (E)-3-((2-hydroxybenzylidene)amino)-5,5′-dimethylimidazolidine-2,4-dione (SB2) and (E)-3-((4-(dimethylamino)benzylidene)amino)-5,5′-dimethylimidazolidine-2,4-dione (SB4) and intermediate processes for the remaining compounds.