Photopatternable Thermochromism Enabled by an Anthracene Heterodimer Ligand

Shortwave ultraviolet light retrocyclizes anthracene dimers (dianthracenes) to their corresponding monomers in the solid state, changing their solubility, fluorescence, geometry, conjugation, covalency, and more. Dianthracenes are thus an ideal building block for intrinsically photopatternable functional materials with bespoke optical, electronic, and magnetic properties. Here we present a new strategy to prepare such materials based on a “heterodimer” of anthracene and 9,10-anthracenedicarboxylic acid that allows us to photopattern the thermochromic phase of a Cu MOF in a two-dimensional (2D)-to-2D transformation, i.e., without dimensional reduction. The thermochromic phase can also be accessed by thermal annealing, as the 2D-to-2D nature of the structural transformation prevents melting. Upon retrocyclization, the parent anthracene released from our heterodimer deintercalates from between the 2D sheets, resulting in a massive, highly anisotropic structural rearrangement and remarkable 44% mass loss without crystal destruction. Furthermore, we demonstrate that 4-substituents on the pyridine ligands can be used to tune the thermochromism, which is based on thermal population of the triplet excited state of a Cu paddlewheel dimer.