Multiphoton-Excited Luminescent Lanthanide Bioprobes: Two- and Three-Photon Cross Sections of Dipicolinate Derivatives and Binuclear Helicates

摘要

Multiphoton excited luminescent properties of water-soluble Eu~(III) and Tb~(III) complexes with derivatives of dipicolinic acid functionalized with a polyoxyethylene pendant arm and terminal groups, [Eu(L~(OMe))3]~(3-), [Eu(L~(NH2))3]~(3-), and [Tb(L~(OH))3]~(3-), as well as of binuclear helicates with overall composition [Ln2(L~(CX))3] (X = 2,5) are investigated. Characteristic emission from the ~5Do and ~5D4 excited levels of Eu~(III) and Tb~(III) , respectively, upon ≈800 nm excitation results from three-photon absorption (3PA) for [Eu(L~(OMe))3]~(3-), [Eu(L~(NH2))3]~(3-), [Tb(L~(OH))3]~(3-), and [Ln2(L~(C2))3], while luminescence from [Eu2(L~(C5))3] is induced by two-photon absorption (2PA) owing to its 1PA spectrum extending further into the visible. The 3PA cross sections have been determined and are the first ones reported for lanthanide complexes: (i) those of Eu~(III)and Tb~(III) bimetallic helicates [Ln2(L~(C2))3] are 20 times larger compared to the corresponding values for tris(dipicolinates); (ii) derivatization of dipicolinic acid for Tb~(III) complexes has almost no influence on the 3PA cross section; however, for Eu~(III) complexes a ～2 times decrease is observed. The feasibility of [Eu2(L~(C5))3] as multiphoton luminescence bioprobe is demonstrated by two-photon scanning microscopy imaging experiments on HeLa cells incubated with this bimetallic helicate.