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 (L1)/presence (L2) 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 1O2 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 1O2 generation properties of L2Gd micellar suspension under two‐photon activation leads to tumour cell death, suggesting the potential of such structures for theranostic applications.