Conformational Locking by Design: Relating Strain Energy with Luminescence and Stability in Rigid Metal–Organic Frameworks

Minimization of the torsional barrier for phenyl ring
flipping
in a metal–organic framework (MOF) based on the new ethynyl-extended
octacarboxylate ligand H8TDPEPE leads to a fluorescent
material with a near-dark state. Immobilization of the ligand in the
rigid structure also unexpectedly causes significant strain. We used
DFT calculations to estimate the ligand strain energies in our and
all other topologically related materials and correlated these with
empirical structural descriptors to derive general rules for trapping
molecules in high-energy conformations within MOFs. These studies
portend possible applications of MOFs for studying fundamental concepts
related to conformational locking and its effects on molecular reactivity
and chromophore photophysics.