EuIII functionalized silica nanoparticles encapsulating chiral CrIII complexes with simultaneous unpolarized red and polarized NIR-I luminescence

Abstract

In this contribution we report on the synthesis and characterization of NIR-I luminescent silica nanoparticles doped with the chiral luminescent Cr^IIIN₆ complex [Cr(dqp)₂]³⁺ (dqp = 2,6-di(quinolin-8-yl)pyridine), Cr@SiO₂NPs, as well as on their post-functionalization with the highly luminescent Eu(tta)₃(phen-Si) (tta = 2-Thenoyltrifluoroacetonate; phen-Si = phenanthroline silica precursor), EuCr@SiO₂NPs. These hybrid materials were prepared via reverse micelle techniques. Electronic microscopy analyses determined an average particle size of 94 nm with the Cr complex randomly distributed into the silica matrix. The EuCr@SiO₂NPs material displays the characteristic ruby-like emission arising from the metal-centered spin-flip transitions within the 730–750 nm range (13 500–12 700 cm⁻¹) together with the Eu-centered ⁵D₀ → ⁷F_J (J = 0–4) transitions in the red region of the electromagnetic spectrum. CPL measurements showed two mirror-image polarized bands ascribed to the Cr(²E → ⁴A₂) and Cr(²T₁ → ⁴A₂) with dissymetry factor (g_lum) in the range of 0.1–0.2. The encapsulated Cr^III complex showed larger quantum yield (4%) and longer excited state lifetime (336–1500 μs) compared to the non-encapsulated complex, providing an enhanced CPL brightness of 80 M⁻¹ cm⁻¹ in aerated media. Thus, these hybrid materials display an efficient and bright long-lived dual simultaneous non-polarized red and polarized NIR-I luminescence.