Breaking the 1,2-HOPO barrier with a cyclen backbone for more efficient sensitization of eu(III) luminescence and unprecedented two-photon excitation properties

Abstract

A cyclen backbone was utilized to study the effect of backbone rigidity on Eu(III) luminescence sensitization using a 1,2-HOPO derivative and 2-thenoyltrifluoroacetonate (TTA) as chromophores. The restriction of molecular movement of Eu-Cy-HOPO brought about by the increased rigidity provided a tightly packed coordination environment for the octadentate Eu(III) center which resulted in the highest overall quantum yield (30.2%) and sensitization efficiency (64.6%) among 1,2-HOPO sensitized Eu(III) complexes. Eu-Cy-HOPO is also the first 1,2-HOPO-based lanthanide complex to emit Eu(III) luminescence under two-photon excitation.