Symmetry rules for the determination of the intercalation geometry of host/guest systems using circular dichroism: A symmetry-adapted coupled-oscillator model

The intercalation of an achiral guest molecule into a relatively complex chiral host system (e.g., DNA, cyclodextrins) leads to an induced circular dichroism (ICD) of the guest transitions. By exploiting the recently developed generalized selection rules, it is shown that the coupled-oscillator expressions for the guest ICD may be analytically symmetry-adapted for all combinations of host/guest symmetries, leading to a rigorous simplification of the expressions and, more importantly, well-defined conditions under which simple correlations exist relating the ICD sign directly to the intercalation geometry. The results are applied to aromatic guests intercalated into DNA and cyclodextrin hosts, as well as to charge-transfer transitions in chiral metal chelate complexes. Good agreement with experimental results is obtained.