A potential nonlinear optical material for crown-porphyrin complexes: Alkali metal doping and transition metal introducing

Abstract

Crown ethers have inspired the rapid growth of research interest in the design and synthesis of functional materials due to their exceptional affinity for metal. In this work, a fascinating crown-porphyrin (Cr-Pr) complexes were studied with doping alkali metal (potassium, K atom) on the crown ether face and introducing transition metal (zinc, Zn atom) on the porphyrin face. The research reveals that the Cr-Pr complex with doped K and Zn atoms results in significant variations in nonlinear optical (NLO) properties. Interestingly, the crown ether ring with the K atom in the K@Cr-Pr complex leads to a remarkable first hyperpolarizability (βtot). On the contrary, when introducing the Zn atom in porphyrins, the Cr-Pr@Zn complex exhibits no significant change in NLO response. Further, the combination of the K and Zn atoms in crown-porphyrin complex (K@Cr-Pr@Zn) can result in significant enhancement of their NLO characteristics, which is much greater than that of the K@Cr-Pr and the Cr-Pr@Zn complexes. The natural population analysis (NPA) and the molecular electrostatic potential maps (ESP) show that the doping of the K atom regulates effectively charge distribution in the complexes. Moreover, the great βtot value can be further illustrated by their low transition energies and an obvious charge transfer (CT) transition in the main excited states. Therefore, the current work achieves that the NLO properties of crown ether derivatives can be regulated by doping alkali metals in the crown ether ring and provides a theoretical guide for developing high-performance NLO devices.