Highly symmetric Ln(iii) boron-containing macrocycles as bright fluorophores for living cell imaging

Abstract

Boron-assisted highly symmetric lanthanide (Ln) macrocycles, (η²-catechol-μ-catecholborate)₃Ln(Ph₃PO)₂·xC₇H₈ (Ln = Dy, x = 0, Dy-B-Ph₃PO; Ln = Yb, x = 1, Yb-B-Ph₃PO) have been achieved by a one-pot reaction of Ln[N(TMS)₂]₃ (TMS = –SiMe₃) with excess catecholborane (HBCat) in the presence of Ph₃PO. Both macrocycles exhibit high brightness and long lifetimes benefitting from the combination of the rigid molecular backbone and the diminishing detrimental high energy X–H (X = C, N and O) vibrations. In particular, Dy-B-Ph₃PO exhibited the longest ⁴F_9/2 lifetime beyond 200 μs to date. When (4-(anthracen-9-yl)phenyl)diphenylphosphine oxide (AnPh₃PO) was used as the antenna ligand, a highly luminescent NIR bioprobe, Yb-B-AnPh₃PO, showing no apparent cell toxicity and high quality in vitro imaging, was obtained. Furthermore, the synthetic versatility of this system permits additional investigations of multifunctional Ln molecular materials in the future.