(669b) Understanding Structure-Property Relationship of Metal-Organic Frameworks and Their Efficiency on Second Harmonic Generation

Metal-Organic frameworks have an enormous potential for non-linear optics due to the unlimited number of possibilities for the fabrication of MOFs. Ab-initio calculations can provide a valuable tool to explore and predict optical properties. Several factors, such as non-centrosymmetricity, donor-acceptor bonds in the network, the strength of the push-pull effect induced by the ligand, the functional group of the ligand, the guest molecules in the structure, and the temperature, can all significantly affect the generation of the Second Harmonic Generation (SHG)¹. Our work focuses on understanding the efficiency of SHG on factors such as different arrangements of ligands within the crystal and temperature. Understanding these effects can offer insight into the structure-property relationships relevant to the SHG, paving the way for discovering novel metamaterials that are SHG efficient and guiding the crystal growth efforts correctly.

In this work, we have studied the different possible orientation of ligands in Zn(3-ptz)₂ MOFs (as shown in Fig. 1A). We compute the effective nonlinearity (d_eff)^2,3 for these structures by contracting the full second-order polarizability tensor estimated using CRYSTAL17. We observe that the effective nonlinearity is dependent on the orientation of the ligands. We calculate the Density of states and Band structure calculation to explain the observed phenomena. To study the effect of temperature on SHG for different systems, we have extracted different configurations, as shown in Fig 1B, from Molecular Dynamics (MD) simulations and computed the d_eff. We observe that the deff is significantly dependent band structure, density of states and the orientation of the ligands.

References:

[1] L. R. Mingabudinova, V. V. Vinogradov, V. A. Milichko, E. Hey-Hawkins, A. V. Vinogradov, “Metal-organic frameworks as competitive materials for non-linear optics”, Chem. Soc. Rev. 2016, 45, 5408.

[2] Y. Shih, “Entangled biphoton source-property and preparations”, Reports on Progress in Physics, 2003, 66, 1009-1044.

[3] R.A. Fritz, Y. J. Colón, F. Herrera, “Engineering entangled photon pairs with metal-organic frameworks”, Chem. Sci., 2021, 12, 3475-3482.