Exceptional Two‐ to Five‐Photon Absorption at Mono/Bis(Donor)‐Porphyrin‐Mono/Bis(Donor) Triads and Pentads

Abstract

Abstract Porphyrins are key components of biologically‐active molecules involved in oxygen transport, light harvesting, and electron transfer; their photophysical properties are consequently of considerable fundamental interest. We herein report that certain donor‐porphyrin‐donor triads and bis(donor)‐porphyrin‐bis(donor) pentads exhibit nonlinear optical activity toward femtosecond pulsed radiation over the spectral range 800–2150 nm. We show that these triads and pentads exhibit unusually strong molecular quadratic optical nonlinearity, two‐photon absorption, and three‐photon absorption, and represent a new molecular motif exhibiting four‐photon absorption. We also report the first porphyrins, and therefore a new class of molecule, to exhibit five‐photon absorption. The two‐, three‐, four‐, and five‐photon absorption maxima are found close to the corresponding multiples of intense linear absorption bands that time‐dependent density functional theory assigns as admixtures of porphyrin‐localized π* ← π and donors‐to‐porphyrin charge‐transfer transitions in the case of the donor‐porphyrin‐donor triads.