Multiphoton absorption at metal alkynyl complexes

Materials exhibiting multi-photon absorption (MPA) are of significant interest for a range of applications including microfabrication, bio-imaging and sensing, and photodynamic therapy. Amongst the possible MPA materials, metal alkynyl complexes have attracted significant recent interest because the collinear metal and alkynyl ligand promote strong electron delocalization and intra-molecular charge transfer, resulting in complexes that can display outstanding MPA behavior. This review summarizes recent progress with metal alkynyl complexes as potential MPA materials, with an emphasis on structure-MPA property relationships that signpost the route to efficient multi-photon absorbers. A brief introduction to the theory of nonlinear optics that underpins MPA and an overview of the key experimental techniques to determine molecular MPA properties are also provided.