Lanthanide contraction-driven modulation of photoswitchable macrocyclic complexes reveals unprecedented glass-induced re-isomerization and luminescence thermometry

Abstract

Designing light-responsive supramolecular architectures with lanthanide ions offers a promising route towards multifunctional materials with tunable photophysical properties. Here, we report a systematic investigation across the lanthanide series of macrocyclic complexes incorporating azobenzene-functionalized diaza-crown ether ligands. We show that subtle changes in the ionic radius across the Ln³⁺ series dictate conformational preferences and modulate trans-to-cis photoisomerization efficiency under UV and visible light. Surprisingly, we uncover that the reverse cis-to-trans isomerization, which is here unresponsive to thermal or photonic stimuli, is uniquely triggered upon contact with glass surfaces, revealing a previously overlooked route for controlling molecular photoswitching. Additionally, selected complexes display efficient visible and near-infrared emission leveraged for robust luminescent thermometric behaviour in the solid state, with tunable sensitivity linked to the lanthanide ions. These findings advance the field of light-driven supramolecular materials and demonstrate how careful molecular-level design of lanthanide–azobenzene assemblies enables control over photoswitching, luminescence and thermal sensing properties, highlighting glass-mediated re-isomerization as a novel phenomenon with implications for future photoresponsive materials.