Highly efficient visible light sensitized red emission from europium tris[1-(4-biphenoyl)-3-(2-fluoroyl)propanedione](1,10-phenanthroline) complex grafted on silicananoparticles

Abstract

A novel class of efficient visible light sensitized antenna complexes of Eu³⁺ based on the use of a highly conjugated β-diketonate, namely, 1-(4-biphenoyl)-3-(2-fluoroyl)propanedione (HBFPD) and 1,10-phenanthroline as an ancillary ligand has been designed, synthesized, characterized and their photophysical properties (PL) investigated. PL measurement results indicated that suitably expanded π-conjugation in the complex molecules makes the excitation band red shift to the visible region and hence the Eu³⁺ complexes exhibit intense red emission under blue light excitation (440 nm) with a solid-state quantum yield of 32 ± 3%, which is the highest so far reported in the literature. Further, in the present work, the visible sensitized Eu³⁺complex has been covalently anchored to the ordered mesoporous MCM-41 via the modified HBFPD ligand for the first time to the best of our knowledge. β-Diketonate grafted to the coupling agent 3-(triethoxysilyl)propylisocyanate was used as the precursor for the preparation of mesoporous nanomaterials. MCM-41 consisting of ternary complex Eu(SiBFPD)₃(phen) covalently bonded to the silica-based network, which was designated as Eu(SiBFPD)₃(Phen)/MCM-41 (3), was obtained by interacting europium nitrate, SiBFPD-Na and 1,10-phenanthroline into the hybrid material via a ligand-exchange reaction. The designed material was further characterized by powder X-ray diffraction, dynamic light scattering (DLS) technique, thermogravimetric analysis, N₂ adsorption-desorption, SEM, TEM, FT-IR, FT-Raman, ¹³C and ²⁹Si CPMAS NMR and photoluminescence spectroscopic techniques. The hybrid material covalently bonded to MCM-41 exhibits an efficient intramolecular energy transfer process from the silylated β-diketonate to the central Eu³⁺, namely, the “antenna effect”, which favored a stronger red/orange intensity ratio, longer lifetime, and high thermal stability than the precursor complex.