Photoswitchable europium complexes for application in photo-activated localization microscopy

Bisthienylethenes (BTEs) are a family of photoswitches that has received great interest the past decade on account of the potential for incorporation into a variety of applications (memory devices, molecular imagining, functional polymers), as well as their extremely high thermal stability and excellent fatigue resistance, compared to their photochromic counterparts. Few BTEs have been complexed with metals, very few to none have been bound to lanthanides. Complexation with lanthanides allows for metal sensitization, while the introduction of photochromic ligands would represent a new class of switchable emission, by turning lanthanide luminescence “on” and “off.” Herein we describe the synthesis and photochromic properties of two dipyridophenazine-based, BTE-type ligands which exhibit reversible photochromism and fluorescence. The respective europium(III) complexes were synthesized and the photophysics were characterized, displaying europium luminescence and photochromism.