A "Multi-Heavy-Atom" Approach Toward Biphotonic Photosensitizers With Improved Singlet Oxygen Generation Properties.

Two trispicolinate 1,4,7-triazacyclonane (TACN)-based ligands bearing three picolinate biphotonic antennae were synthetized and their Yb3+ and Gd3+ complexes isolated. One series differs from the other by the absence (L-1)/presence (L-2) of bromine atoms on the antenna backbone, offering respectively improved optical and singlet-oxygen generation properties. Photophysical properties of the ligands, complexes and micellar Pluronic suspensions were investigated. Complexes exhibit high two-photon absorption cross-section combined either with NIR emission (Yb) or excellent O-1(2) generation (Gd). The very large intersystem crossing efficiency induced by the combination of bromine atom and heavy rare-earth element was corroborated with theoretical calculations. The O-1(2) generation properties of (LGd)-Gd-2 micellar suspension under two-photon activation leads to tumour cell death, suggesting the potential of such structures for theranostic applications.