Diquat Derivatives: Highly Active, Two-Dimensional Nonlinear Optical Chromophores with Potential Redox Switchability

In this article, we present a detailed study of structure−activity relationships in diquaternized 2,2′-bipyridyl (diquat) derivatives. Sixteen new chromophores have been synthesized, with variations in the amino electron donor substituents, π-conjugated bridge, and alkyl diquaternizing unit. Our aim is to combine very large, two-dimensional (2D) quadratic nonlinear optical (NLO) responses with reversible redox chemistry. The chromophores have been characterized as their PF_6^− salts by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. Their visible absorption spectra are dominated by intense π → π^* intramolecular charge-transfer (ICT) bands, and all show two reversible diquat-based reductions. First hyperpolarizabilities β have been measured by using hyper-Rayleigh scattering with an 800 nm laser, and Stark spectroscopy of the ICT bands affords estimated static first hyperpolarizabilities β_0. The directly and indirectly derived β values are large and increase with the extent of π-conjugation and electron donor strength. Extending the quaternizing alkyl linkage always increases the ICT energy and decreases the E_(1/2) values for diquat reduction, but a compensating increase in the ICT intensity prevents significant decreases in Stark-based β_0 responses. Nine single-crystal X-ray structures have also been obtained. Time-dependent density functional theory clarifies the molecular electronic/optical properties, and finite field calculations agree with polarized HRS data in that the NLO responses of the disubstituted species are dominated by ‘off-diagonal’ β_(zyy) components. The most significant findings of these studies are: (i) β_0 values as much as 6 times that of the chromophore in the technologically important material (E)-4′-(dimethylamino)-N-methyl-4-stilbazolium tosylate; (ii) reversible electrochemistry that offers potential for redox-switching of optical properties over multiple states; (iii) strongly 2D NLO responses that may be exploited for novel practical applications; (iv) a new polar material, suitable for bulk NLO behavior

Evolution of Linear Absorption and Nonlinear Optical Properties in V-Shaped Ruthenium(II)-Based Chromophores

In this article, we describe a series of complexes with electron-rich cis-{Ru^(II)(NH_3)_4}^(2+) centers coordinated to two pyridyl ligands bearing N-methyl/arylpyridinium electron-acceptor groups. These V-shaped dipolar species are new, extended members of a class of chromophores first reported by us (Coe, B. J. et al. J. Am. Chem. Soc. 2005, 127, 4845−4859). They have been isolated as their PF_6− salts and characterized by using various techniques including ^1H NMR and electronic absorption spectroscopies and cyclic voltammetry. Reversible Ru^(III/II) waves show that the new complexes are potentially redox-switchable chromophores. Single crystal X-ray structures have been obtained for four complex salts; three of these crystallize noncentrosymmetrically, but with the individual molecular dipoles aligned largely antiparallel. Very large molecular first hyperpolarizabilities β have been determined by using hyper-Rayleigh scattering (HRS) with an 800 nm laser and also via Stark (electroabsorption) spectroscopic studies on the intense, visible d → π^* metal-to-ligand charge-transfer (MLCT) and π → π^* intraligand charge-transfer (ILCT) bands. The latter measurements afford total nonresonant β_0 responses as high as ca. 600 × 10^(−30) esu. These pseudo-C_(2v) chromophores show two substantial components of the β tensor, β_(zzz) and β_(zyy), although the relative significance of these varies with the physical method applied. According to HRS, β_(zzz) dominates in all cases, whereas the Stark analyses indicate that β_(zyy) is dominant in the shorter chromophores, but β_(zzz) and β_(zyy) are similar for the extended species. In contrast, finite field calculations predict that β_(zyy) is always the major component. Time-dependent density functional theory calculations predict increasing ILCT character for the nominally MLCT transitions and accompanying blue-shifts of the visible absorptions, as the ligand π-systems are extended. Such unusual behavior has also been observed with related 1D complexes (Coe, B. J. et al. J. Am. Chem. Soc. 2004, 126, 3880−3891)

Illuminating of mild steel/HCI interface in the presence of 5-DAT inhibitor

International audienceIn this article, a novel and non-toxic Schiff base containing multi-heteroatom coded with the name 5-DAT (5-(4-(diethylamino)benzylidene)amino)-1,3,4-thiadiazole-2-thiol is designed as the corrosion inhibitor for mild steel (MS) in 1.0 M HCl. The structure of Schiff base is illuminated by NMR, FT-IR, UV spectrophotometers and theoretical (Gaussian and Monte Carlo) calculations. Electrochemical techniques were utilized to determine the inhibition efficiency of synthesized Schiff base on mild steel corrosion. The surface of the MS was characterized by scanning electron microscopy. The inhibition talent of the 5-DAT was described by electrochemical impedance spectroscopy, lineer polarization resistance, and potentiodynamic polarization techniques. 5-DAT synthesized in this study showed high efficiency with 98.9% inhibition efficiency since it contains high electron density heteroatoms such as nitrogen, sulfur and many multiple bonds, which are considered as more adsorption centers compared to the previous ones. While 5-DAT shows efficiency at 298 K, according to EIS and LPR results, respectively, 98.41, 98.12; It was observed that the efficiency was not lost much with 93.87, 92.86 efficiencies at 328 K. The presence of a 5-DAT film, which is homogeneously dispersed on the surface, protects the metal surface against corrosion

Nonlinear refraction and absorption activity of dimethylaminostyryl substituted BODIPY dyes

International audienceOptical and nonlinear optical properties of difluoroboradiazaindacene (BODIPY) models with attached dimethylaminostyryl substituents were studied. The optical absorption and fluorescence emission of BODIPY compounds were found to be dependent on the number of dimethylaminostyryl substituents. In order to investigate the nonlinear refraction and absorption activity, the Z-scan technique was used employing a laser generating a wavelength at 532 nm with 30 ps pulse duration. The studied dimethylaminostyryl containing BODIPY compounds showed considerable nonlinear refraction and reverse saturable absorption. The BODIPY containing a pair of dimethylaminostyryl substituents demonstrated an increased third order nonlinear optical response mostly due to the extension of its conjugated length. © 2016 The Royal Society of Chemistry

Chiral side groups trigger second harmonic generation activity in 3D octupolar bipyrimidine-based organic liquid crystals

The design of efficient noncentrosymmetric materials remains the ultimate goal in the field of organic second-order nonlinear optics. Unlike inorganic crystals currently used in second-order nonlinear optical applications, organic materials are an attractive alternative owing to their fast electro-optical response and processability, but their alignment into noncentrosymmetric film remains challenging. Here, symmetry breaking by judicious functionalization of 3D organic octupoles allows the emergence of multifunctional liquid crystalline chromophores which can easily be processed into large, flexible, thin, and self-oriented films with second harmonic generation responses competitive to the prototypical inorganic KH2 PO4 crystals. The liquid-crystalline nature of these chiral organic films also permits the modulation of the nonlinear optical properties owing to the sensitivity of the supramolecular organization to temperature, leading to the development of tunable macroscopic materials.status: publishe

Effect of metal complexation on the nonlinear optical response of a conjugated ligand

International audienceOrganic nonlinear optical materials are widely investigated materials for fabricating optoelectronic devices. Particularly organic π-conjugated systems as well as transition metal complex compounds are studied in this direction because of the strong electronic coupling between the ligand and the metal, their excellent chemical stability, and their rich photochemical and photophysical properties. In this work, comparative studies of the third-order nonlinear optical susceptibilities of a bipyridine ligand (4-(N,N-dibutylamino)-4′-(5-ethynyl-2,2′-bipyridine)-azobenzene (A) and of the corresponding heteroleptic ruthenium complex (Ru(bpy)2(La)(PF6)2 (B) (La signifies the ligand) are presented. The NLO properties were investigated by means of the Z-scan technique using a 30 ps mode-locked Nd-YVO4 laser at 532 nm with a repetition rate of 10 Hz. Our results show that the introduction of the metal in the organic complex results in a significant modification of the third-order nonlinear optical response

Neutral copper(I) complexes featuring phosphinesulfonate chelates

International audienceThe reaction of diphenylphosphinobenzenesulfonic acid with copper(i) oxide resulted in the formation of the new neutral dimeric copper(I) complex {Cu2(DPPBS)2·MeOH)2}. X-ray diffraction studies revealed that the complex has a dimeric structure and a pyramidal trigonal geometry around the copper atom which contains coordinated methanol molecules at the copper centers. Cleavage of the dimer by reaction with various bipyrimidines enabled the preparation of the corresponding well-defined heterotopic mononuclear [Cu(P^O)(N^N)] and dinuclear {(P^O)Cu(N^N)Cu(P^O)} complexes. X-ray crystal structure determination shows these to have distorted tetrahedral geometries. Their absorption and emission properties were investigated experimentally and photophysical data were also confirmed by DFT and TD-DFT calculations. Owing to the methanol molecules, the neutral crystalline dimer {Cu2(DPPBS)2·(MeOH)2} displays green reversible photoluminescence upon UV irradiation in the solid state with an absolute luminescence quantum yield of 0.5