Giant Multi‐Photon Absorption by Heptazine Organometalation

Multi‐photon absorption (MPA) is of increasing interest for applications in technologically important “windows” of the electromagnetic spectrum (near‐infrared III, NIR‐III, 1550–1870 nm; and the new 2080–2340 nm region); however, few molecules exist that display strong MPA at these long wavelengths. We herein report the syntheses of the first 2,5,8‐s‐heptazine‐cored organometallic complexes, together with organic analogues. The complexes exhibit outstanding 3PA cross‐sections in the NIR‐III and exceptional 4PA cross‐sections in the new 2080–2340 nm window. We demonstrate that replacing organic donor groups by organometallic units results in an order of magnitude increase in 3PA, the “switching on” of 4PA, and a dramatic improvement in photo‐stability. Our results highlight the impressive outcomes possible with an “organometalation” approach to NLO materials design.