Inclusion Complexes of Dyes and Cyclodextrins: Modeling Supermolecules by Rigorous Quantum Mechanics

The results of structure optimization and molecular dynamics simulationof host-guest -cyclodextrin-pinacyanol dye inclusion complexesare obtained by applying a density functional based tight-binding code.The results attempt to correlate UV/Vis and circular dichroism spectraldata with calculated aggregate structures of the sandwich dimer, withthe monomers twisted slightly against each other. The sense of twist ispredetermined by the chirality of the complexing host. The UV/Vis-spectralare interpreted using the exciton model. Within this model, each excitedstate of the monomer generates two excitonic states in the dimer. Theinteraction between the two monomers results then in a Davydov splittingof the two dimer states. The opposite signs of the two dimer states can beattributed to the twist of the monomers when they interact.