Visible-light excited red emitting luminescent nanocomposites derived from Eu3+-phenathrene-based fluorinated β-diketonate complexes and multi-walled carbon nanotubes

Abstract

A novel β-diketone ligand, 4,4,5,5,5-pentafluoro-3-hydroxy-1-(phenanthren-3-yl)pent-2-en-1-one (Hpfppd), which contains a polyfluorinated alkyl group, as well as a conjugated phenanthrene unit, has been synthesized and utilized for the construction of two new europium coordination compounds [Eu(pfppd)₃(H₂O)₂] 1 and [Eu(pfppd)₃(tpy)] 2 (where tpy = 2,2′:6,6′′-terpyridine). The designed europium compounds were well characterized and their solid-state photoluminescence (PL) properties were examined. Notably, the introduction of a highly conjugated phenanthrene moiety into the 3-position of the β-diketonate ligand remarkably extends the excitation window of the corresponding Eu³⁺ complexes towards the visible region (up to 500 nm). The PL study demonstrated that the replacement of high-energy oscillators O–H (water molecules) in 1 with an ancillary ligand terpyridine leads to an impressive enhancement in both overall quantum yield (from 31 to 75%) and ⁵D₀ lifetime (from 0.51 to 1.04 ms) values. To the best of our knowledge, the solid-state quantum yield of 2 is found to be the highest so far reported in the literature under blue-light excitation (415 nm). To gain a wider applicability and also to overcome the poor thermal, photochemical and mechanical stabilities of Eu³⁺–β-diketonate luminophores, in the present study, a nanocomposite material (1@oxMWCNTs) has been fabricated by coupling Eu³⁺ complex 1 onto an oxidized multi-walled carbon nanotube (oxMWCNTs) scaffold. Characterization of the new luminescent nanocomposite material was accomplished by means of FT-IR, FT-Raman, XPS, TGA, SEM, TEM, AFM, EDAX and photoluminescence spectroscopic techniques. The designed nanocomposites 1@oxMWCNTs exhibit high thermal stability and luminescence efficiency. Furthermore, the high dispersibility of luminescent 1@oxMWCNTs in a polymer matrix (PMMA) and intense red emissions make it a promising luminophore for applications in polymer optical fibers as well as in light emitting devices.