Green approach to new library of 1,8-naphthalimide fluorophores employing C-C and C-N cross coupling reactions by novel, durable, and reusable magnetic nanocatalyst bearing nickel (0) complex of 1,10-phenanthroline

Abstract

The novel light cayn to yellow fluorescent 1,8-naphthalimide-based compounds with benzothiophene, benzofuran, aryl, and amino substituent at the C-4 position were successfully synthesized in excellent yields (up to 97 % yield) via the catalysed Suzuki coupling and carbon–nitrogen cross coupling reactions using a novel heterogeneous super nanomagnetic Ni-catalyst system bearing fortified 1,10-phenanthroline ligand (Fe3O4@SiO2-Phen-Ni(0)) under mild conditions. The structure of synthesized magnetic nanocatalyst was identified by FT-IR, XRD, FESEM, DLS, TEM, VSM, TGA-DSC, EDX, mapping images, ICP, and UV–Vis techniques, which exhibited high efficiency in the synthesis of these C-4 π-conjugated and amino fluorophore 1,8-naphthalimide materials with low Ni-contamination. The nanocatalyst with the aid of an external magnet could be easily recovered and reused for up to nine consecutive runs without significant decline in its activity. UV–Vis absorption and fluorescence emission spectrum of these derivatives were collected. All these compounds can emit light cay, greenish-yellow or yellow emission and show a large Stokes shift (νa-νf up to 8900 cm−1), longer λ emission (λem up to 541 nm), and fluorescence quantum yield (Qf) (up to 0.89) due to the extended conjugation system. The provided data of Suzuki derivatives reveal the highest Qf and λem in EtOH solvent, and 4-amino-1,8-naphthalimide derivatives exhibit, the highest Qf data in DCM solvent, and the largest emission wavelength in acetonitrile, and the highest data of Stokes shift in EtOH. Furthermore, the positive solvatochromic behavior, corresponding to bathochromic shift with increasing solvent polarity, in new C4-aryl/ heteroaryl/ and amino 1,8-naphthalimide frameworks was shown.