Highly polar molecular systems are needed for many practical applications based on light-matter interactions, from solar-energy utilization to molecular electronics. Novel insertion complexes of non- and polar molecules non-covalently trapped between metal-halide (MX) counter-ions are designed and their properties investigated computationally. The M-molecule-X systems can be meta- or stable by up to 1 eV relative to molecule + MX. The polar-molecule insertion complexes can be even more bound than the common “attached” MX-molecule conformers and separated from those by significant energy barriers (by up to ~1 eV), thus being thermodynamically stable species with huge dipoles of up to &gt; 25 D.<br/>Interesting features include the nonobvious contributions of the molecule’s dipole moment to the system stability and polarity, the cooperativity of pair interactions, the inversion of ionic-neutral dissociation channels, the reshaping up to isomerization of the molecule due to framing ion-pairs. The IR spectra are predicted to considerably vary and sensitively indicate the formation of both the M-molecule-X and MX-molecule conformers, with intensities up to an order of magnitude higher in the complexes, facilitating their reliable detection and differentiation in experiments.<br/>The above suggests a way of adding polarity to nonpolar molecules and thus of enabling their efficient experimental detection and characterization. The resulting increased attraction could promote molecular self-assembly and chemical reactions as well. The latter is exemplified by isomerization of a trapped hydrocarbon molecule, with the related barriers significantly altered due to a combination of the counterions’ pressure and electric field in this field-promoted mechanochemical process. Its IR signature is also predicted. Finally, the metastable systems suggest at possible applications for high-capacity energy storage.

Counterion trapping of molecules: Enhanced IR activity and internal field-assisted isomerization in extremely polar complexes

ACS Fall 2021

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