Dual emissive ytterbium(III) complexes with π-conjugated BODIPY-bipyridine ligands

Four BODIPY-functionalized bipyridine ligands (B1, B2, B3 and B4) were synthesized for sensitizing the near-infrared emission of Yb(III) ions. In these ligands, a BODIPY moiety was conjugated to 2,2'-bipyridine through an acetylene spacer at its C2 position, whereas its C6 position was substituted by H (B1), iodine (B2), 4-carboxylphenylacetylene (B3) or 4-thiocyanophenylacetylene (B4). The ligands exhibit strong absorption in the visible region and readily form stable complexes with ytterbium(III) trishexafluoroacetylacetonate (hfac-) hydrate in dichloromethane. Single-crystal X-ray diffraction analysis for Yb-B2 showed that the BODIPY unit almost falls into the bipyridine plane with Yb(III) being coordinated by six O from hfac- and two N atoms from bipyridine. All complexes exhibit strong absorption between 530 and 570 nm and can sensitize the ytterbium(III) for its emission at 980 nm under the UV-VIS light illumination. Interestingly, the visible emission from the complex increased when excited at 375 nm, making the complexes dual emissive, which is due to the increased absorption of the complex at 375 nm and inefficient energy transfer from the BODIPY moiety to the Yb(III) ion.

Lanthanide complexes with an azo-dye chromophore ligand: syntheses, crystal structures, and near-infrared luminescence by long-wavelength excitation

Near-infrared (NIR) emissive probes are becoming increasingly popular in biological sensing and imaging due to the advantages of non-invasiveness and deep tissue-penetrating ability. Herein, a series of complexes of trivalent lanthanide ions (Ln = Yb, Er, and Gd) with the commercially available azo dye chromophore 2R (Na2H2C2R) as ligand and featuring respectively H2O and dimethylsulfoxide (DMSO) as ancillary ligands have been prepared. Formulated as [Ln2(HC2R)2(H2O)10]·8H2O (1-3, Ln = Yb, Er, Gd) and [Ln2(HC2R)2(DMSO)10]·2DMSO (4-6, Ln = Yb, Er, Gd), their structures have been determined by single-crystal X-ray diffraction studies. Photophysical property studies revealed NIR emissions of the DMSO complexes characteristic of Yb(III) and Er(III), effectively sensitized by the dye ligand arising mainly from the π-π* transition of the chromophore. The long-wavelength excitation of the complexes, covering the whole visible-light range and extending into the NIR region, portends the potential applications of such complexes for flexible bioimaging and sensing.

Lanthanide porphyrinoids as molecular theranostics

In recent years, lanthanide (Ln) porphyrinoids have received increasing attention as theranostics. Broadly speaking, the term 'theranostics' refers to agents designed to allow both disease diagnosis and therapeutic intervention. This Review summarises the history and the 'state-of-the-art' development of Ln porphyrinoids as theranostic agents. The emphasis is on the progress made within the past decade. Applications of Ln porphyrinoids in near-infrared (NIR, 650-1700 nm) fluorescence imaging (FL), magnetic resonance imaging (MRI), radiotherapy, and chemotherapy will be discussed. The use of Ln porphyrinoids as photo-activated agents ('phototheranostics') will also be highlighted in the context of three promising strategies for regulation of porphyrinic triplet energy dissipation pathways, namely: regioisomeric effects, metal regulation, and the use of expanded porphyrinoids. The goal of this Review is to showcase some of the ongoing efforts being made to optimise Ln porphyrinoids as theranostics and as phototheranostics, in order to provide a platform for understanding likely future developments in the area, including those associated with structure-based innovations, functional improvements, and emerging biological activation strategies.