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Abstract Dynamic photoactuating crystals have become a sensation due to their potential applications in developing smart medical devices, molecular machines, artificial muscles, flexible electronics actuators, probes and microrobots. Here we report the synthesis of two iso-structural metal-organic crystals, [Zn(4-ohbz)2(4-nvp)2] (1) and [Cd(4-ohbz)2(4-nvp)2] (2) {H4-ohbz = 4-hydroxy benzoic acid; 4-nvp = 4-(1-naphthylvinyl)pyridine} which undergo topochemical [2 + 2] cycloaddition under UV irradiation as well as sunlight to generate a dimerized product of discrete metal-complex [Zn(4-ohbz)2(rctt-4-pncb)] {rctt-4-pncb = 1,3-bis(4′-pyridyl)-2,4-bis(naphthyl)cyclobutane} (1′) and one-dimensional coordination polymer (1D CP) [Cd(4-ohbz)2(rctt-4-pncb)] (2′) respectively, in a single-crystal-to-single-crystal (SCSC) process. The Zn-based compound demonstrates photosalient behaviour, wherein crystals show jumping, splitting, rolling, and swelling upon UV irradiation. However, the Cd-based crystals do not show such behaviour maintaining the initial supramolecular packing and space group. Thus the photomechanical behaviour can be induced by choosing a suitable metal ion. The above findings are thoroughly validated by quantitative density functional theory (DFT) calculations which show that the Zn-based crystal shifts towards an orthorhombic structure to resolve the anisotropic UV-induced mechanical strain. Furthermore, the mechano-structure-property relationship has been established by complimentary nanoindentation measurements, which are in-line with the DFT-predicted single crystal values.

Piezoelectric materials which are non-toxic and eco-friendly are of interest. Here, the authors report on the creation of collagen-mimetic peptides which can be self-assembled into piezoelectric materials and study the design characteristics required for optimized power generation.

Biological piezoelectric materials are beginning to gain attention for their huge potential as eco-friendly energy harvesting materials. In particular, simple amino acid and peptide crystal assemblies are demonstrating large voltage outputs under applied force, and high sensitivity when detecting vibrations. Here we utilise Density Functional Theory (DFT) calculations to quantitatively predict the energy harvesting properties of two understudied proteinogenic amino acid crystals: L-Arginine and L-Valine. The work highlights the ability of quantum mechanical calculations to screen crystals as high-performance energy harvesters, and demonstrates the capability of small biological crystals as eco-friendly piezoelectric materials. L-Arginine is predicted to have a maximum piezoelectric voltage constant of gij = 274 mV m/N, with a Young’s Modulus of E = 17.1 GPa. L-Valine has a maximum predicted piezoelectric voltage constant of gij = 62 mV m/N, with a calculated Young’s Modulus of E = 19.8 GPa.