"2D Cocrystallization Of Hydrogen Bonding Molecules with Strong Polarization"
presented by:
Professor Daniel P. Miller, PhD
Department of Chemistry, Hofstra University
Abstract: Croconic Acid (CA), a known organic ferroelectric with a computed dipole moment of 4.0-6.0 D, and 4,6-diaminobenzene-1,3-dione (i.e. C6H2(...NH2)2(...O)2), being a p-benzoquinonemonoimine zwitterion derivative (PZI) with a large computed/experimental dipole of 8.2 D / 12 D, forms an ordered two-dimensional 2D hydrogen bonding cocrystal through adsorption to an Au(111) surface. The hydrogen bonds exhibited by the 2D CA-PZI cocrystal are of type O-H---O and N-H---O, with CA-PZI cocrystals predicted to form through the binding energy of the isolated CA-PZI dimer being preferred over unimolecular CA and unimolecular PZI. Scanning Tunneling Microscopy (STM) imaging of the deposited organic molecules on the Au(111) surface found two unique structures for the CA-PZI cocrystal that are independent of attempts at editing the stoichiometric ratio of the two molecules. Dispersion-corrected Density Functional Theory (DFT-D) computational modeling was able to elucidate upon the overall structure of both networks, The charge and proton transfers in the 2D CA-PZI were analyzed and found that CA readily transfers one proton to PZI, with relative ease (global minimum), through a hydrogen bonding structural transfer from O-H---O to O---H-O and creating a negatively and positively charged CA and PZI, respectively. The induced polarization switches upon such proton transfer shifts in 2D CA-PZI are associated with strong dipole moments, potentially forming 1,3-dihydroxy-4,6-diaminobenzene from CA proton donation, with the largest polarization values associated with structures that may easily be obtained with an external electric field.
