Regulating the NLO response of anthraquinone-supported thiourea-linked crown ether macrocycle by introducing metal cations: A DFT study

Abstract

Recently, an anthraquinone-supported thiourea group linking a 1-aza-18-crown-6 macrocycle L has been the subject of extensive attention due to the perfect affinity towards metal cations. This work systematically researched the effects of different metal cations ([Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text]) on the second-order nonlinear optical (NLO) properties of macrocycle L by density functional theory (DFT). DFT calculations revealed that the values of first hyperpolarizabilities ([Formula: see text] decrease significantly when alkaline earth metal cations ([Formula: see text] and [Formula: see text]) were injected into macrocycle L due to the smaller charge transfer (CT) transition and larger transition energy. Conversely, the variations of [Formula: see text] values in alkali metal cations ([Formula: see text] and [Formula: see text] and transition metal cations ([Formula: see text] and [Formula: see text]) derivatives are not obvious compared to the [Formula: see text] value of macrocycle L. Therefore, the NLO properties of macrocycle can be effectively regulated by alkaline earth metal cations. Furthermore, we found that the [Formula: see text] value of anion-controlled complex Na(L)(ClO4) is larger than that of L*Na+ complex because the anion [Formula: see text] improves the planarity of anthraquinone-supported thiourea group leading to the enhancement of the CT ability. In addition, the influence of frequency-dependent on the first hyperpolarizabilities is weak for the current systems. Hence, we look forward to the conception of this work will offer a fundamental guideline and reference for further research for novel NLO materials.