A Metallosupramolecular Receptor for Squaraine Dyes Enabling Ultrafast Dark Resonance Energy Transfer

Abstract

ABSTRACT A metal‐organic cage was obtained by combining acridone‐based dipyridyl ligands with Pd 2+ ions. The cage acts as a potent receptor for squaraine dyes, with a pronounced preference for guests with 2,6‐dihydroxyphenyl substituents. This selectivity profile differs from that of previously reported receptors for squaraine dyes. The acridone‐based cage itself is non‐emissive. Upon its photoexcitation, ultrafast (sub‐ps) dark resonance energy transfer (DRET) to the encapsulated squaraine dyes was observed, resulting in bright, near‐infrared guest emission, with pseudo‐Stokes shifts of up to 440 nm. Upon binding of a chiral dye, chirality transfer to the host could be evidenced by circular dichroism spectroscopy.