Chiroptical Activity from an Achiral Biological Metal–Organic Framework

Chiroptical activity is observed
from an achiral adenine-containing
metal–organic framework (MOF) named ZnFDCA. Such a seemingly
counterintuitive phenomenon can, in fact, be predicted by the intrinsic
crystal symmetry of 4̅2m point group. Although
theoretically allowed, examples of optically active achiral crystals
are extremely rare. ZnFDCA is the first reported achiral MOF showing
optical activity, as demonstrated by a pair of circular dichroism
signals with opposite signs and enhanced intensity. Moreover, simply
through adding an amino substituent to adenine, the chiroptical activity,
as well as nonlinear optical activity, of the analogous MOF, namely
ZnFDCA-NH2, disappears due to diverse packing pattern giving
rise to centrosymmetric crystal symmetry.