DFT study of transition metals doped calix-4-pyrrole with excellent electronic and non-linear optical properties

Abstract

Herein a detailed comparative study on the transition metal doped calix-4-pyrrole was carried out to determine the optical, electronic, and non-linear optical (NLO) properties, as well as to synthesize some thermodynamically stable complexes. All the computational work was accomplished using density functional theory (DFT). The optical and chemical properties of Sc[CPM1]Sc, Ti[CPM1]Sc, Sc[CPM1]Ti, and Ti[CPM1]Ti were seen to be superior to the un-doped cage. Doping of transition metals inside and outside the cage increased the diffused excess electrons, as a result lowering the energy gap (from 4.01 to 2.15 eV). Due to these excess electrons and lower excitation energy, noteworthy increasement took place in the polarizability and hyperpolarizability of all doped structures. The minimum energy gap (2.15 eV) and largest first hyperpolarizability (16360 a.u) was observed for Sc[CPM1]Sc. Non-covalent interaction (NCI) analysis illustrated that the intermolecular forces are the major cause of interaction between the cage and dopants. It was also indicated from the density of state (DOS) and frontier molecular orbital (FMO) diagrams that the transition metals significantly raised the distribution of charge density in the structures under study, especially in Sc[CPM1]Sc, while the capability to transfer charges was revealed from transition density matrix (TDM) graphs. Natural bond orbital (NBO) charge analysis revealed that transfer of charges occurred from the dopants towards the surface. Calculated values of interaction energy, binding energy, and vertical ionization potential confirmed the thermo-dynamical stability of the molecules. Time-dependent DFT measures were conducted to evaluate all the necessary transitions and absorption analysis. Consequently, all the calculated parameters praised the capability of our designed molecules in the field of electronics and non-linear optics.