TDDFT studies on the structures and ECD spectra of chiral bisarylimidos bearing different lengths of o-alkoxy chain-substituted polyoxomolybdates

The chiroptical properties of bisarylimidos bearing o-alkoxy chain-substituted polyoxomolybdates [Mo6O17(2,2′-NC6H4OCnH2nOC6H4N)]2− [n = 4(2), 6(3±), 8(4)] were investigated using the time-dependent density functional method. The results showed that the studied chiral polyoxometalates (POMs) manifested similar absorption sites but displayed different shapes and magnitudes in their electronic circular dichroism (ECD) spectra. The ECD spectra of the studied chiral POMs originated from charge-transfer (CT) transitions from arylimido fragments to the POM cages and from oxygen atoms to the molybdenum atoms in the POM cages. The o-alkoxy chain served as a scaffold for generating chirality rather than contributing to the ECD spectrum of the studied POMs. The induced chiralities of the POM cages were defined by the CT transitions, which were completely localized on the POM cages. Furthermore, the long-range corrected CAM-B3LYP hybrid functional and a basis set that is larger than Lanl2DZ should be used for ECD calculations of chiral POMs. Our work establishes the use of computational studies to investigate the chiroptical properties of chiral POMs and provides theoretical interpretations.

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► The geometry, electronic, and chiroptical properties of polyoxometalatocyclophanes are studied.
► The rigidity of POM in solution leads to the intramolecular chirality.
► The ECD spectra of POMs vary in signs and magnitudes, while show similar absorption sites.
► The o-alkoxy chain is scaffold for generating chirality, rather than contributes to ECD absorption.
► The induced chirality of POM cage is confirmed by electron transition assignment.