A Piezoelectric Ionic Cocrystal of Glycine and Sulfamic Acid

Abstract

Cocrystallization of two or more molecular compounds can dramatically change the physicochemical properties of a functional molecule without the need for chemical modification. For example, coformers can enhance the mechanical stability, processability, and solubility of pharmaceutical compounds to enable better medicines. Here, we demonstrate that amino acid cocrystals can enhance functional electromechanical properties in simple, sustainable materials as exemplified by glycine and sulfamic acid. These coformers crystallize independently in centrosymmetric space groups when they are grown as single-component crystals but form a noncentrosymmetric, electromechanically active ionic cocrystal when they are crystallized together. The piezoelectricity of the cocrystal is characterized using techniques tailored to overcome the challenges associated with measuring the electromechanical properties of soft (organic) crystals. The piezoelectric tensor of the cocrystal is mapped using density functional theory (DFT) computer models, and the predicted single-crystal longitudinal response of 2 pC/N is verified using second-harmonic generation (SHG) and piezoresponse force microscopy (PFM). The experimental measurements are facilitated by polycrystalline film growth that allows for macroscopic and nanoscale quantification of the longitudinal out-of-plane response, which is in the range exploited in piezoelectric technologies made from quartz, aluminum nitride, and zinc oxide. The large-area polycrystalline film retains a damped response of ≥0.2 pC/N, indicating the potential for application of such inexpensive and eco-friendly amino acid–based cocrystal coatings in, for example, autonomous ambient-powered devices in edge computing.

Modulating the Electromechanical Response of Bio-Inspired Amino Acid-Based Architectures through Supramolecular Co-Assembly

“…In the present work, then we added a new summary of how the current dataset adds to the knowledge on electromechanical properties, demonstrating the generality of our co-assembly approach to studying structure–function relations. Looking at our models across this study and our previous co-crystal work, ,,, clear trends are beginning to emerge regarding structural and chemical features that modulate the piezoelectric performance of bio-inspired co-crystals. (i) Co-crystallization can lower the symmetry of the system to maximize the number of nonzero piezoelectric constants, providing multiple actuation directions that can be exploited in devices.…”

Minimalistic Metabolite‐Based Building Blocks for Supramolecular Functional Materials

“…Furthermore, the properties of metabolite self‐assembled materials can be modulated by intermolecular stacking modes [7,23] . The single crystals of glycine and sulfamic acid have centrosymmetric structure, but the ionic cocrystals formed by both components at a 2 : 1 ratio have a non‐centrosymmetric structure and exhibit a significant lateral piezoelectric response of 2 pC/N [24] . We investigated the co‐crystallization of the endogenous metabolite L‐AcA with achiral photosensitive bipyridine derivatives (BPE) [25] .…”

“…[7,23] The single crystals of glycine and sulfamic acid have centrosymmetric structure, but the ionic cocrystals formed by both components at a 2 : 1 ratio have a non-centrosymmetric structure and exhibit a significant lateral piezoelectric response of 2 pC/N. [24] We investigated the co-crystallization of the endogenous metabolite L-AcA with achiral photosensitive bipyridine derivatives (BPE). [25] The stable trans conformation of the BPE molecule was retained in the co-crystal, and L-AcA formed a stable strong dimer through two intermolecular hydrogen bonds.…”

Piezoelectric Response of Plastic Ionic Molecular Crystals: Role of Molecular Rotation

“…The group of C[NH 2 ] 3 -compounds consists of three plastic ionic molecular crystals built up of a C[NH 2 ] 3 - Most theoretical studies on piezoelectricity have focused on inorganic materials or polymers. While piezoelectric properties of some molecular crystals have been investigated [82][83][84][85][86][87][88][89], microscopic insight into piezoelec-tric mechanisms for these materials is vital for designing new and better materials. Plastic crystals are molecular crystals characterized by the existence of orientationally disordered mesophases, triggered by the onset of rotational motion.…”