Pentacyanoiron(II) as an Electron Donor Group for Nonlinear Optics:  Medium-Responsive Properties and Comparisons with Related Pentaammineruthenium(II) Complexes

Abstract

In this article, we describe a series of complex salts in which electron-rich {FeII(CN)5}3- centers are coordinated to pyridyl ligands with electron-accepting N-methyl/aryl-pyridinium substituents. These compounds have been characterized by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. Molecular quadratic nonlinear optical (NLO) responses have been determined by using hyper-Rayleigh scattering (HRS) at 1064 nm, and also via Stark (electroabsorption) spectroscopic studies on the intense, visible d → π* metal-to-ligand charge-transfer (MLCT) bands. The relatively large static first hyperpolarizabilities, β0, increase markedly on moving from aqueous to methanol solutions, accompanied by large red-shifts in the MLCT transitions. Acidification of aqueous solutions allows reversible switching of the linear and NLO properties, as shown via both HRS and Stark experiments. Time-dependent density functional theory and finite field calculations using a polarizable continuum model yield relatively good agreement with the experimental results and confirm the large decrease in β0 on protonation. The Stark-derived β0 values are generally larger for related {RuII(NH3)5}2+ complexes than for their {FeII(CN)5}3- analogues, consistent with the HRS data in water. However, the HRS data in methanol show that the stronger solvatochromism of the FeII complexes causes their NLO responses to surpass those of their RuII counterparts upon changing the solvent medium.

High-Performance Switching of Bulk Quadratic Nonlinear Optical Properties with Large Contrast in Polymer Films Based on Organic Hydrogen-Bonded Ferroelectrics

“…10 Such NLO-switching generally depends on reversible modification of molecular hyperpolarizability using chemical methods, such as photochromism, 11,12 redox reaction, 13,14 and proton-transfer process. 15 Whereas, in solid-state materials, centrosymmetric crystallization of NLO-active moieties extends the disadvantage to the bulk switchable NLO properties (i.e. second-harmonic generation, SHG).…”

Excited States from Time‐Dependent Density Functional Theory

“…Most are in the linear response regime. In inorganic chemistry, the optical response of many transition metal complexes [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] has been calculated, as have some X-ray absorption spectra. 36,37 In organic chemistry, heterocycles [38][39][40][41][42][43] have been examined among others, [44][45][46] including the response of thiouracil, 47 s-tetrazine, 48 and annulated porphyrins.…”

DFT Study of the Structure, Reactivity, Natural Bond Orbital and Hyperpolarizability of Thiazole Azo Dyes

“…Our calculated total hyperpolarizabilities of the three dyes in chloroform are in good match with the measured ones in the same solvent [31]. In addition, the estimated total hyperpolarizabilities of the three dyes in CCl 4 , CHCl 3 , CH 2 Cl 2 and DMSO solvents using CAM-B3LYP/6-311++G** level of theory, listed in Table 5, are dictated by the polarity of these solvents, that is, the solvatochromic behaviours of the dyes have brought about pronounced NLO characteristics [47]. As Table 3, Table 4 and Table 5 show, the values of total hyperpolarizabilities of the three dyes (A, B and C) are inversely proportional to the magnitude of the energy gaps [51,52,53].…”

“…As Table 5 shows, the HOMOs and LUMOs of the dyes are further stabilized relative to the polarity of the solvents, with the latter being greatly affected. It seems, then, that the solvatochromic behaviour could have resulted mainly from the relatively strong interactions between these solvents and the indandione, malononitrile and dicyanovinylindanone acceptor moieties [47]. …”