Beschreibung:
<jats:title>Abstract</jats:title><jats:p>Very large molecular two‐ and three‐photon absorption cross‐sections are achieved by appending ligated bis(diphosphine)ruthenium units to oligo(<jats:italic>p</jats:italic>‐phenyleneethynylene) (OPE)‐based “stars” with arms up to 7 phenyleneethynylene (PE) units in length. Extremely large three‐ and four‐photon absorption cross‐sections, through the telecommunications wavelengths range and beyond, are obtained for these complexes upon optimizing OPE length and the ruthenium‐coordinated peripheral ligand. Multi‐photon absorption (MPA) cross‐sections are optimized with stars possessing arms 2 PE units in length. Peripheral ligand variation modifies MPA merit and, in particular, 4‐nitrophenylethynyl ligand incorporation enhances maximal MPA values and “switches on” four‐photon absorption (4PA) in these low molecular‐weight complexes. The 4‐nitrophenylethynyl‐ligated 2PE‐armed star possesses a maximal four‐photon absorption cross‐section of 1.8×10<jats:sup>−108</jats:sup> cm<jats:sup>8</jats:sup> s<jats:sup>3</jats:sup> at 1750 nm, and significant MPA activity extending beyond 2000 nm.</jats:p>