Single molecule piezoelectrics and ferroelectrics: from theory to experiment

This dissertation proposes and studies the idea of single molecule piezoelectrics and ferroelectrics via both computational and experimental means. The research is aimed to open a new area of piezoelectric/ferroelectric materials for next generation of nanoscale, flexible, efficient, and multifunctional electronic devices. Density functional theory (DFT) calculations are employed to study the electric field induced conformational change (piezoelectric effect) of three molecular springs: asymmetrically substituted helicenes, asymmetrically substituted phenanthrenes, and oligoaminoacids and the electric field driven polarization inversion (ferroelectric effect) of molecular bowls (buckybowls). Molecular structure, functional groups, dipole moment, and regiochemistry are discussed as factors to generate good single molecule piezoelectrics and ferroelectrics. A significantly large piezoelectric coefficient (up to 272 pm/V for a hypothetical helicene derivative and 450 pm/V for a hypothetical buckybowl derivative) and a broad range of inversion field (0.26 V/nm - 9.05 V/nm for buckybowls) are predicted. Our proposed materials could potentially compete with conventional piezo/ferroelectric materials (e.g. zinc oxide (ZnO), polyvinylidene difluoride (PVDF), and lead zirconium titanate (PZT), etc.). The piezoelectric effect of single molecules are experimentally demonstrated with a sample of patterned self-assembled monolayers (SAMs) of oligoaminoacids via techniques of piezoresponse force microscopy (PFM) and Fourier-transform infrared spectroscopy (FTIR). Combined with our computational predictions, we believe that a new class of piezoelectric/ferroelectric materials may be created from the “bottom up” based on molecular conformational changes, which are new material resources for fabricating flexible, large scale, ultrathin, and lightweight electronic devices