Three-dimensional through-space/through-bond derealization in cyclophane systems: A molecuie-in-molecule approach

In this article, we propose a simple strategy to identify the nature of excitonic couplings in a series of cyclophanedienes based on the "molecule-in-molecule" (MIM) theory. The contributions of charge-transfer (CT) exciton, unavailable by the commonly used supermolecular approach due to the inadequate basis set, can be unambiguously identified within this methodology. Combining the CT contributions calculated on the cyclophanedienes and the corresponding hypothetical molecules with tethers removed, one can infer the information on the relative importance of through-bond and through-space contributions in the low-lying excited states. Particularly, we discovered that the tether effect for the meta-linkage cyclophanedienes is crucial, whereas those for para-linkage cyclophanedienes are vanishingly small. The changes in the coupling between two moieties for both the six-membered meta-linkage and five-membered cyclophanedienes arise primarily from an increase in the through-bond charge-transfer component of the coupling (>70%). Within the MIM model, the derealization pathway of the dimer in the excited state can be explained quantitatively by a CT exciton, which differs from the approach based on the conventional orbital interaction analysis.