Theoretical investigation of electronic structures, second-order NLO responses of cyclometalated Ir(iii) and Rh(iii) counterpart complexes: effect of metal centers

Tuning center metal is an effective manner to modulate second-order NLO responses. When the big size Ir is introduced in complexes, the superior NLO responses can be found over its Rh counterparts.

A New Imaginary Term in the Second-Order Nonlinear Susceptibility from Charged Interfaces

Nonresonant second harmonic generation (SHG) phase and amplitude measurements obtained from the silica-water interface at varying pH values and an ionic strength of 0.5 M point to the existence of a nonlinear susceptibility term, which we call χ_X⁽³⁾, that is associated with a 90° phase shift. Including this contribution in a model for the total effective second-order nonlinear susceptibility produces reasonable point estimates for interfacial potentials and second-order nonlinear susceptibilities when χ_X⁽³⁾ ≈ 1.5χ_water⁽³⁾. A model without this term and containing only traditional χ⁽²⁾ and χ⁽³⁾ terms cannot recapitulate the experimental data. The new model also provides a demonstrated utility for distinguishing apparent differences in the second-order nonlinear susceptibility when the electrolyte is NaCl versus MgSO₄, pointing to the possibility of using heterodyne-detected SHG to investigate ion specificity in interfacial processes.

The second-order NLO property of a photoswitchable heteroditpioc ion-pair receptor based on 2-pyridyl acylhydrazone linking with 2,6-pyridine bisamide: The impacts of metal cations and anions

A photoswitchable heteroditpioc ion-pair receptor E-1 and its isomeride Z-1 (without the anion binding site), that are based on the 2-pyridyl acylhydrazone linking 2,6-pyridine bisamide, have brought our attention to systematically explore the second-order nonlinear optical (NLO) properties by the density functional theory (DFT). In this work, we mainly studied the influences of metal cations (M = Na⁺, K⁺, Mg²⁺, Ca²⁺, Hg²⁺ and Pb²⁺), anions (X = Cl^-, Br^- and I^-) and ion-pair (NaCl, NaBr and NaI) on NLO responses for the receptor. In addition, the impacts of isomerization and poto-switching processes on NLO response for these systems also have been discussed detailedly. The results show that the isomerization process does not effectively adjust the NLO properties for our studied systems. But the poto-switching process that was triggered by light to capure or release ions plays an important role in improving the NLO properties. The receptors E-1 and Z-1 are excellent candidates to effectively detect metal cation Pb²⁺, because the first hyperpolarizability (β_tot) values of E∗Pb²⁺ and Z∗Pb²⁺ increased by 13 times and 20 times relative to that of receptors E-1 (188.06 a.u.) and Z-1 (270.21 a.u.), respectively. In addition, the receptor E-1 has the possibility to detect anion I^- due to the larger β_tot values compared with other anion-complexes. However, the changes of NLO responses for ion-pair complexes are not obvious compared with corresponding anion-complexes. We are looking forward to the research would be beneficial for further theoretical and experimental studies on recognizing metal cations and anions based on large second-order NLO difference.

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

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.

Comparative cation sensing properties of a newly designed urea linked ferrocene-benzimidazole dyad: a DFT study

Herein, our primary motivation was to elucidate the electronic and physicochemical properties of a novel molecular dyad consisting of ferrocene (Fc; electron donor), urea (u; linker), and amphoteric benzimidazole (BI; electron acceptor) entities. The sensor responses were investigated for various divalent transition metal cations (Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺) and the selectivity of this cationophore molecule (Fc-u-BI) to copper ion (Cu²⁺) was demonstrated by using B3LYP/LANL2DZ method. According to the thermochemical calculations, we justified that Fc-u-BI⋯Cu²⁺ reached to the lowest binding energy (∆E), enthalpy (∆H), and Gibbs free energy (∆G) changes. In the light of the calculated global descriptors, Fc-u-BI⋯Cu²⁺ was found to be the softer and thus the most reactive complex. The complex stabilities and their corresponding non-covalent interactions were also investigated by NBO and NCI analyses, respectively. The mechanistic insight into metal cation sensing by the modeled cationophore dyad.

Redox-triggered switch based on platinum(ii) acetylacetonate complexes bearing an isomeric donor–acceptor conjugation ligand shows a high second-order nonlinear optical response

Pt(ii) acetylcetonate complexes with an isomeric D–A ligand exhibiting exceptionally large hyperpolarizabilities are promising redox-triggered NLO switches.