Outstanding Multi-Photon Absorption at π-Delocalizable Metallodendrimers.

Multi-photon absorption (MPA) has attracted interest for applications exploiting the tight spatial control of interaction volume and long wavelength excitation. However, a deficiency of molecules exhibiting higher-order nPA (n-photon absorption, n>2) and a lack of structure-property studies to define the key structural characteristics needed to optimize higher-order MPA performance have hindered practical development. We herein report the syntheses of second- and third-generation metallodendrimers and assessment of their nonlinear absorption, together with those of zero- and first-generation analogues. We report the first 5PA and 6PA data for an organometallic. The largest dendrimer exhibits exceptional three-, four-, five- and six-photon absorption to femtosecond-pulsed light. The systematically varied compounds highlight the crucial role of metal-to-oligo(phenyleneethynylene) charge transfer in promoting outstanding MPA activity.