Synthesis and photochemical behavior of donor–acceptor systems obtained from chloro-1,4-naphthoquinone attached to trans-aminostilbenes

2-Chloro-1,4-naphthoquinone was covalently attached to six differently substituted and positional isomers of trans-aminostilbene, forming a novel donor–acceptor system (QST), in which a good fluorophore is bonded via an NH group to an active redox quencher. The new systems were characterized by FT-IR, 1H NMR, HR-MS, UV–Vis and fluorescence spectroscopy. The redox state of the system QST/QH2ST controls its photochemical properties. While the QSTʹs behave as an ‘auto-quenching system’ and are non-fluorescent, the reduced hydroquinonic system (QH2ST) affects appreciably the emission properties of the molecule.