Abstract
Although lanthanide double-decker complexes with hetero-macrocyclic ligands as functional luminescent and magnetic materials have promising properties, their inferior water solubility has negated their biomedical applications. Herein, four water-soluble homoleptic lanthanide (
Ln
=
Gd
,
Er
,
Yb
and
La
) sandwiches with diethylene-glycol-disubstituted porphyrins (
DD
) are reported, with their structures proven by both quantum chemical calculations and scanning tunneling microscopy. Our findings demonstrate that the near-infrared emission intensity and singlet oxygen (
1
O
2
) quantum yields of
YbDD
and
GdDD
in aqueous media are higher than those of the reported capped lanthanide monoporphyrinato analogues,
YbN
and
GdN
; the brightness and luminescence lifetime in water of
YbDD
are greater than those of
YbN
. This work provides a new dimension for the future design and development of molecular theranostics-based water-soluble double-decker lanthanide bisporphyrinates.
Tweaking the chemical structure of naturally occurring rings called porphyrins has improved the biocompatibility of molecular probes that emit bright light at low doses. Recent studies have shown that rare earths can act as potent sources of near-infrared light when they are attached to porphyrin ‘antennas’ that transfer absorbed light energy to the metal. Ka-Leung Wong from Hong Kong Baptist University and co-workers have now developed porphyrin—rare earth complexes that can easily enter aqueous environments such as bodily fluids. The team synthesized water-friendly porphyrins by adding short diethylene glycol chains to the ring framework, and used them to trap rare earths including ytterbium into sandwich-shaped arrangements. Characterizations revealed the new complexes retained their efficient, long-lasting light emissions in aqueous solutions, and could act as generators of electronically excited oxygen for photodynamic therapy.