Jeff Mottishaw - Effects of Aromatic Trifluoromethylation, Fluorination, and Methylation on Intermolecular π-π Interactions.

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      Publication Details (including relevant citation   information):

      The Journal of Physical Chemistry A 2013, 117 (33), 7970–7979.

      Abstract:

        Marcus theory states that the rate of charge transfer is directly   proportional to the amount of intermolecular orbital overlap.   Theoretically optimizing the electronic coupling through the   orientation and distance which both can increase the frontier   orbital overlap between molecules is an attractive route to   potentially provide theoretical insight for discovering new high   performance semiconductor materials. To investigate how these   parameters qualitatively affect charge transfer of model systems,   unconstrained dimer optimizations with MP2 and   dispersion-corrected DFT methods were used to probe the π–π   interactions of methylated, fluorinated, and trifluoromethylated   benzene, pyridine, and bipyridine dimers. These systems can serve   as simplified models representing weak noncovalent interactions   in organic semiconductor materials. Enhanced intermolecular   interaction energies, reduced π–π distances, and more favorable   cofacial orientations were found with the trifluoromethylated   dimers compared to fluorinated and methylated dimers studied.   Similar effects were found with donor–acceptor pairs that   represent organic p-n heterojunction systems. These enhanced π–π   interactions are likely caused by increased molecular quadrupole   moment and dispersion interaction associated with   trifluoromethylation. This computational study illustrates the   strong potential of trifluoromethylation and, possibly   perfluoroalkylation of acenes and heteroacenes, leading   qualitatively to enhanced electron transfer through better π–π   stacked structures, making them viable candidates for use as   n-type organic semiconductor materials. The findings also provide   insight for fundamental interactions between drug molecules that   include fluorinated and trimethylfluorinated aromatics binding to   protein receptors.

      Address (URL): http://pubs.acs.org/doi/abs/10.1021/jp403679x