Intraligand Charge Transfer Research Articles

Two Zinc(II) Complexes with 1D Chain and 2D Layer Directed by Competitive Coordination of the Mixed Ligands: Syntheses, Crystal Structures, and Fluorescent Properties

Two new competitive coordination-directed zinc(II) complexes, [Zn2(bpp)2(na)4]n (1) and [Zn(bpp)2(nas)2]n (2) (bpp = 1,3-bi(4-pyridyl)propane, na− = 1-naphthoate, and nas− = 2-aminonaphthalene-1-sulfonate), were hydrothermally synthesized by varying carboxylate- or sulfonate-containing coligands. Structural analyses reveal that complex 1 modified by terminal na− spacers possesses a bent one-dimensional chain bridged by ditopic bpp linkers. By contrast, complex 2 with two monodentate nas− ligands exhibits a two-dimensional layered structure extended by four equatorial bpp connectors. Obviously, the increase on the dimensionality of 2 than 1 is significantly resulting from the competitive coordination of the two mixed ligands with differently tunable binding groups to variable metal polyhedra. In addition, both complexes with analogously high thermal stability display strong fluorescent emissions at room temperature resulting from the ligand-to-metal or intraligand charge-transfer, suggesting their hopeful applications as efficient fluorescent materials.

Effect of substituent groups with two types on benzene ring on photoluminescence property of complexes of benzoic acid—Functionalized polystyrene with Eu(III) Ion

Abstract Two benzoic acid derivatives, methoxybenzoic acid (MOBA) and formylbenzoic acid (FBA), on whose benzene ring, an electron-donating substituent group (methoxy group) and an electron-withdrawing substituent group (formyl group) exist, respectively, were bonded onto the side chains of polystyrene (PS) through polymer reactions, obtaining two benzoic acid derivative-functionalized PSs, PS-MOBA and PS-FBA. The two macromolecule ligands were made to coordinate to Eu 3+ ion, preparing two binary polymer-rare earth complexes, PS-(MOBA) 3 -Eu(III) and PS-(FBA) 3 -Eu(III) as well as two ternary complexes with phenanthroline (Phen) as the second small-molecule ligand. The luminescence property of theses complexes was mainly examined, and the effect of the two types of substituent groups on the benzene ring of the bonded benzoic acid on the photo physical behavior of these complexes was investigated in depth. The experimental results show that both the two types of substituent groups on the benzene ring of the bonded benzoic acid can effectively strengthen their fluorescence emission intensities, but the mechanisms are different. For MOBA series complexes, through p-π conjugation effect between methoxy group and the π orbit of the bonded ligand MOBA, the triplet state level of the bonded ligand MOBA can be remarkably decline, so the energy level matching degree between the triplet state level of the bonded ligand MOBA and the resonant energy level of Eu(III) ion is greatly enhanced, resulting in a drastically enhancing of the luminescence intensities of the MOBA series complexes. For FBA series complexes, through n–π* transition between the formyl group and π* orbit of the bonded ligand FBA and the accompanying intraligand charge transfer, the triplet state energy of the bonded ligand FBA can also be reduced, and the energy level matching degree can also be improved, leading to an obvious enhancement of luminescence intensities of the complexes.

Cyclometalated Iridium(III) Complexes Containing 4,4'-π-Conjugated 2,2'-Bipyridine Derivatives as the Ancillary Ligands: Synthesis, Photophysics, and Computational Studies.

This article demonstrates a series of cyclometalated Ir(III) complexes of the type [Ir(III)(C^N)2(N^N)](PF6), where C^N is 2-phenylpyridine, and N^N corresponds to the 4,4'-π-conjugated 2,2'-bipyridine ancillary ligands. All these compounds were synthesized through splitting of the binuclear dichloro-bridged complex precursor, [Ir(C^N)2(μ-Cl)]2, with the appropriate bipyridine ligands followed by the anion exchange reaction. The linear and nonlinear absorption properties of the synthesized complexes were investigated. The absorption spectra of all the title complexes exhibit a broad structureless feature in the spectral region of 350-700 nm with two bands being well-resolved in most of the cases. The structures of all the compounds were modeled in dichloromethane using the density functional theory (DFT) algorithm. The nature of electronic transitions was further comprehended on the basis of time-dependent DFT analysis, which indicates that the origins of various bands are primarily due to intraligand charge transfer transitions along with mixed-metal and ligand-centered transitions. The synthesized compounds are found to be nonemissive at room temperature because of probable nonradiative deactivation pathways of the T1 state that compete with the radiative (phosphorescence) decay modes. However, the frozen solutions of compounds Ir(MS 3) and Ir(MS 5) phosphoresce at the near-IR region, the other complexes remaining nonemissive up to 800 nm wavelength window. The two-photon absorption studies on the synthesized complexes reveal that values of the absorption cross-section are quite notable and lie in the range of 300-1000 GM in the picosecond case and 45-186 GM in the femtosecond case.

Aggregation‐Induced Phosphorescent Emission from ReI Complexes: Synthesis and Property Studies

AbstractFour ReI complexes with aggregation‐induced phosphorescent emission (AIPE) were synthesized with the formula Re(CO)3(Bath‐n)Br (n = 1–4), where Bath‐1 = 4,7‐diphenyl‐2‐[4‐(trimethylsilyl)‐phenyl]‐1,10‐phenanthroline (1), Bath‐2 = 4,7‐diphenyl‐2‐[4‐(dimethylphenylsilyl)phenyl]‐1,10‐phenanthroline (2), Bath‐3 = 4,7‐diphenyl‐2‐[4‐(methyldiphenylsilyl)phenyl]‐1,10‐phenanthroline (3), and Bath‐4 = 4,7‐diphenyl‐2‐[4‐(triphenylsilyl)phenyl]‐1,10‐phenanthroline (4), and fully characterized. The single crystals of 1 and 3 were obtained in the monoclinic crystal system by diffusion of diethyl ether into their dichloromethane solutions. Complexes 1–4 in pure THF (c ≈ 10–5 mol L–1) mainly present π* → π emission at 370 nm and intraligand charge‐transfer (ILCT) emission at 440 nm, whereas the powder samples of 1–4 solely give lower energy 3MLCT (metal‐to‐ligand charge transfer) emission at approximately 560 nm. The lifetimes of the powder samples of 1–4 were measured at room temperature to be 0.335 µs, 0.149 µs, 0.289 µs, and 1.301 µs, respectively. Additionally, the emission spectra and the UV/Vis absorption spectra of 1–4 were analyzed in different THF/H2O mixtures to investigate their AIPE character. Furthermore, the ground states and the UV/Vis absorption spectra of 1–4 were also theoretically simulated at the B3LYP/(LANL2DZ+6‐31G) level.

Binuclear organoplatinum(II) complexes with double bis(diphenylphosphino)acetylene bridges: Synthesis, X-ray structure determination, electronic structures and DFT calculations

The organoplatinum complexes cis-[PtAr2(SMe2)2] (Ar = p–MeC6H4 and p–MeOC6H4) and cis,cis-[Me2Pt(μ-SMe2)2PtMe2] react very easily - in acetone at room temperature - with 1 or 2 equiv 1,1′–bis(diphenylphosphino)acetylene (= dppac), to give the diplatinum(II) complexes [Pt2R4(μ–dppac)2], (1, R = Me; 2, R = p–MeC6H4; 3, R = p–MeOC6H4) in which two square-planar R2Pt units are held together by two bridging dppac ligands. All the complexes were characterized using multinuclear (1H, 31P and 195Pt) NMR spectroscopy and single crystal X-ray structure determination. Investigation of electronic structures and related DFT and TD-DFT calculations supported a mixed 1IL (intraligand charge transfer)/1MLCT (metal-to-ligand charge transfer) for R = Me and L'LCT (ligand-to-ligand charge transfer) for R = p–MeC6H4 and p–MeOC6H4.

Theoretical investigation of non-covalent interactions and spectroscopic properties of a new mixed-ligand Co(II) complex

A new mixed ligand complex formulated as [Co(pydc)(2-apym)(H2O)2]·H2O (1) (pydcH2 = pyridine–2,6–dicarboxylic acid, 2-apym = 2-aminopyrimidine) has been used for density functional theory (DFT) calculations. The neutral monomeric complex participates in a variety of non-covalent interactions including H-bonding and π-stacking to create a 1-D coordination chain. In order to determine the binding energy of the non-covalent interactions responsible for the crystalline network formation of 1 they have been studied by dispersion corrected density functional theory (DFT-D) calculations. For this purpose, the independent smallest fragment (monomer) and subsequently the related network including seven monomers bearing all non-covalent interactions have been optimized. The results demonstrate that hydrogen bonds, especially N–H···O interactions, govern the network formation. The calculated electronic absorption spectrum agrees with experiment in which three major electron-transition bands derived from (σ, p) → π∗ and π → π∗ ligand to ligand charge transfer (LLCT), and π → n and π → π∗ pydc intra-ligand charge transfer (ILCT) transitions are seen.

Two naphthoate-based lead(II) complexes with different limited-nuclear motifs: Syntheses, crystal structures, and fluorescent properties

Two new naphthoate-based lead(II) complexes, [Pb(NA)2(2,2’-Bipy)] (I) and [Pb2(NA)4(4,4’- Bipy)] (II) (NA–= 1-naphthoate, 2,2’-Bipy = 2,2’-bipyridine, and 4,4’-Bipy = 4,4’-bipyridine) (CIF files CCDC nos. 664900 (I), 664899 (II)) have been hydrothermally synthesized by varying the N-heterocyclic coligands. Structural analyses reveal that the two complexes possess different limited-nuclear motifs, the former one owns mononuclear unit and the last complex exhibits centrosymmetric binuclear motif bridged by 4,4’-Bipy connector. The coordination numbers of Pb(II) metal centers in I and II are four and five, respectively. The NA– anions in both complexes show the same binding modes, it is obvious that the bipyridyl coligands in the present mixed-ligands system are responsible for the dissociation or dimerization of mononuclear structural units and the binding numbers of the metal ion. In both complexes, the 6s lone pair of electrons of Pb2+ has a stereochemistry activity resulting the distribution of the Pb–O and Pb–N bonds in a hemisphere. Furthermore, both of the two compounds are linked to 2D network by intermolecular C–H···O hydrogen bonding and π···π stacking interactions, exhibiting strong fluorescent emissions resulting from the NA‒-based intraligand charge transfer at room temperature, which can be hopefully used as fluorescent materials.

Highly Efficient Visible-to-NIR Luminescence of Lanthanide(III) Complexes with Zwitterionic Ligands Bearing Charge-Transfer Character: Beyond Triplet Sensitization.

Two zwitterionic-type ligands featuring π-π* and intraligand charge-transfer (ILCT) excited states, namely 1,1'-(2,3,5,6-tetramethyl-1,4-phenylene)bis(methylene)dipyridinium-4-olate (TMPBPO) and 1-dodecylpyridin-4(1 H)-one (DOPO), have been prepared and applied to the assembly of lanthanide coordination complexes in an effort to understand the ligand-direction effect on the structure of the Ln complexes and the ligand sensitization effect on the luminescence of the Ln complexes. Due to the wide-band triplet states plus additional ILCT excitation states extending into lower energy levels, broadly and strongly sensitized photoluminescence of f→f transitions from various Ln(3+) ions were observed to cover the visible to near-infrared (NIR) regions. Among which, the Pr, Sm, Dy, and Tm complexes simultaneously display both strong visible and NIR emissions. Based on the isostructural feature of the Ln complexes, color tuning and single-component white light was achieved by preparation of solid solutions of the ternary systems Gd-Eu-Tb (for TMPBPO) and La-Eu-Tb and La-Dy-Sm (for DOPO). Moreover, the visible and NIR luminescence lifetimes of the Ln complexes with the TMPBPO ligand were investigated from 77 to 298 K, revealing a strong temperature dependence of the Tm(3+) ((3) H4 ) and Yb(3+) ((2) F5/2 ) decay dynamics, which has not been explored before for their coordination complexes.

A new TPE-based tetrapodal ligand and its Ln(iii) complexes: multi-stimuli responsive AIE (aggregation-induced emission)/ILCT(intraligand charge transfer)-bifunctional photoluminescence and NIR emission sensitization.

A tetrapodal zwitterionic-type ligand featuring both AIE (aggregation-induced emission) and ILCT (intraligand charge transfer) properties, namely 1,1',1'',1'''-(4,4',4'',4'''-(ethene-1,1,2,2-tetrayl)tetrakis(benzene-4,1-diyl))tetrakis(methylene)tetrapyridin-4(1H)-one (TPE-4PO) has been designed and applied to the assembly of lanthanide complexes LIFM-21(Ln) (Ln = Sm, Eu, Gd, Tb and Dy). Apart from sensitization of NIR emission of Sm(3+) and Dy(3+), the resulting ligand and lanthanide complexes show both AIE and ILCT-related photoluminescence behaviors. The photo-response of this system to different aggregation states, solvents' polarity and mechanical grinding was demonstrated by distinguishable emission intensities and colours.

Synthesis and properties of new mononuclear Ru(II)-based photocatalysts containing 4,4'-diphenyl-2,2'-bipyridyl ligands.

The synthesis and characterisation of a series of eleven new 4,4'-diphenyl-2,2'-bipyridyl derivatives (N^N) with varying 4- or 3,5-substituents on the phenyl rings are reported. The molecular structures of two of these compounds, 4,4'-bis(3,5-diheptyloxyphenyl)-2,2'-bipyridyl and 4,4'-bis(3,5-di-4,4,5,5,5-pentafluoropentyloxyphenyl)-2,2'-bipyridyl are confirmed by X-ray crystallography. Fourteen neutral complexes trans-Ru(II)Cl2(N^N)(CO)2 are prepared by reacting the new proligands and three known ones with the polymeric precursor [Ru(II)Cl2(CO)2]n, and their optical and electrochemical properties are studied. Density functional theory (DFT) and time-dependent DFT calculations have been carried out on selected complexes in order to rationalise their electronic structures and absorption properties. The low energy electronic absorption bands have metal-to-ligand charge-transfer and ligand-to-ligand charge-transfer (LLCT) character, but these dominate only in the 4-substituted species. In the 3,5-disubstituted ones, intraligand charge-transfer (ILCT) within the bpy ligands becomes more important. The complexes show only irreversible reductive electrochemistry and no signs of polymerisation. The photocatalytic oxidation behaviour of selected trans-Ru(II)Cl2(N^N)(CO)2 complexes and their mono-aquo derivatives [Ru(II)(H2O)(CO)2Cl(N^N)](+) with 4-methoxybenzyl alcohol is studied. Turnover numbers of up to ca. 130 are achieved when using [Ru(II)(bpy)3](2+) (bpy = 2,2'-bipyridyl) as photosensitizer and [Co(III)(NH3)5Cl](2+) as a sacrificial oxidant.

Two Cadmium(II) Complexes with Polymeric 2D Layer and Discrete Mononuclear Motifs: Syntheses, Crystal Structures, and Fluorescent Properties

Two new 1,3-bi(4-pyridyl)propane-based cadmium(II) complexes, [Cd(Bpp)2(Nas)2]n (I) and [Cd(Bpp)2(Na)2(H2O)2] (II) (Bpp = 1,3-bi(4-pyridyl)propane, Nas– = 2-aminonaphthalene-1-sulfonate, and Na– = 1-naphthoate) (CIF files CCDC nos. 1429589 (I), 1429590 (II)) have been hydrothermally synthesized by varying carboxylateor sulfonate-containing coligands. Structural analyses reveal that, complex I with monodentate Nas– ligands exhibits a two-dimensional (2D) layered motif extended by equatorial Bpp connectors. By contrast, complex II modified by monodentate Na– ligands exhibit discrete mononuclear structure. Althouth the Nas–/Na– coligands showed the same monodentate binding modes, the Bpp ligand exhibits bridging or terminal binding modes in I and II, respectively. So it is obvious that the competitive coordination in the present mixed-ligands system is responsible for the aggregation or dissociation of mononuclear structural units. Furthermore, both of the two compounds are linked to 3D supramolecular architecture by intermolecular C–H···O hydrogen bonding or C–H···π stacking interactions, exhibiting strong fluorescent emissions resulting from the ligand-to-metal or Na‒-based intraligand charge transfer at room temperature, which can be hopefully used as f luorescent materials. DOI: 10.1134/S1070328416070022

Friend or foe? The role of solvents in non-triplet, intraligand charge transfer sensitization of lanthanide(iii) luminescence

A comprehensive photophysical and solvatochromic study is conducted to evaluate the luminescence properties of our Eu(iii), Sm(iii) and Yb(iii) complexes.

Contrasting photophysical properties of rhenium(i) tricarbonyl complexes having carbazole groups attached to the polypyridine ligand.

In the present work, new rhenium(i) polypyridyl compounds, fac-[Re(L)(CO)3(cbz2phen)](+/0) where cbz2phen = 4,7-di(9H-carbazol-9-yl)-1,10-phenanthroline and L = Cl(-), pyridine (py) or 2-aminomethylpyridine (ampy) were synthesized and characterized by (1)H NMR, UV-Vis and IR spectroscopy combined with theoretical calculations using time-dependent density functional theory (TD-DFT). Their photophysical properties were investigated by steady state and time-resolved emission spectroscopy. These compounds show a strong and broad absorption band around 350-500 nm that, also by TD-DFT, corresponds to the carbazol → phenanthroline intraligand charge transfer transition, (1)ILCTcbz2phen, with some contribution of the Re(i) → phenanthroline metal-to-ligand charge transfer transition, (1)MLCTRe→cbz2phen. In contrast to typical Re(i) polypyridyl complexes, cbz2phen-based Re(i) compounds exhibit two emission maxima in CH3CN solution and relatively low emission quantum yields, 10(-3)-10(-2). Solution phase time-resolved photoluminescence and excited state quenching experiments provided meaningful information on the presence of multiple emitter states after light excitation, which were identified as an (1)ILCTcbz2phen excited state deactivation at higher energies and a long-lived phosphorescence attributed to the (3)MLCTRe→cbz2phen excited state. When embedded into a PMMA matrix, the radiative decay from the singlet state is inhibited and the contribution of both (3)MLCT and (3)ILCTcbz2phen to the luminescence is observed. The photophysics of these Re(i) compounds reported herein provide new insights into the understanding of substitutional groups on the polypyridyl ligands that are relevant to practical and fundamental development of photo-induced molecular devices.

Copper(I) complexes of 2-methoxy-(5-trifluoromethyl-phenyl)-pyridine-2yl-methylene-amine: Impact of phosphine ancillary ligands on luminescence and catalytic properties of the copper(I) complexes

Some copper(I) complexes of the type [Cu(L)(PPh3)2]X (X=Cl (1a), CN (1b), ClO4 (1c), BF4 (1d)) and [Cu(L)(dppe)]X (X=Cl (2a), CN (2b), ClO4 (2c) and BF4 (2d)) [where L=2-methoxy-(5-trifluoromethyl-phenyl)-pyridine-2yl-methylene-amine; PPh3=triphenylphosphine; dppe=1,2-bis(diphenylphosphino)ethane] have been prepared and characterized on the basis of elemental analyses, IR, UV–Vis, 1H NMR and 31P NMR spectral studies. The representative complex of the series 1d and 2c are characterized by single crystal X-ray diffraction which reveal that, in each complex the central copper(I) ion assumes the irregular pseudo-tetrahedral geometry. All the complexes display a weak MLCT that varies considerably with phosphine ligands. Quasireversible redox behavior is accounted for all complexes corresponding to Cu(I)/Cu(II) couple and is sensitive to phosphine ligands. All the complexes exhibit blue-green emission originate from intra-ligand charge transfer (ILCT), ligand to ligand charge transfer (LLCT) transitions or mixture of them and vary markedly with the phosphine ligands. The copper(I) complexes with dppe ancillary ligand shows greater activity for the amination of iodobenzene as compared to PPh3 ancillary ligand in the complexes.

Magnetic and Photo-Physical Properties of Lanthanide Dinuclear Complexes Involving the 4,5-Bis(2-Pyridyl-N-Oxidemethylthio)-4′,5′-Dicarboxylic Acid-Tetrathiafulvalene-, Dimethyl Ester Ligand

The reaction between the 4,5-bis(2-pyridyl-N-oxidemethylthio)-4′,5′-dicarboxylic acid-tetrathiafulvalene-, dimethyl ester ligand (L) and the metallo-precursors Ln(hfac)3·2H2O leads to the formation of two dinuclear complexes of formula [Ln2(hfac)6(L)]·(CH2Cl2)·(C6H14)0.5 (LnIII = DyIII (1) and YbIII (2)). The X-ray structure reveals a quite regular square anti-prism symmetry for the coordination sphere of the lanthanide ion. UV-visible absorption properties have been experimentally measured and rationalized by TD-DFT calculations. The functionalization of the tetrathiafulvalene (TTF) core by two methyl ester moieties induces the appearance of an additional absorption band in the lowest-energy region of the spectrum. The latter has been identified as a HOMO (Highest Occupied Molecular Orbital)→LUMO (Lowest Unoccupied Molecular Orbital) Intra-Ligand Charge Transfer (ILCT) transition in which the HOMO and LUMO are centred on the TTF and methyl ester groups, respectively. Irradiation at 22,222 cm−1 of this ILCT band induces an efficient sensitization of the YbIII-centred emission that can be correlated to the magnetic properties.

Tuning a Lanthanide Complex To Be Responsive to the Environment in Solution.

The f-f emissions of lanthanide-ion complexes have predictable emission energies and many practical applications, but the emitting states are generally impervious to the surroundings. This investigation explores ligand- and metal-centered emission processes for a series of mixed-ligand complexes of composition M(X-T)(NO3)3, where the metal ion is europium, gadolinium, terbium, or lutetium, and X-T denotes the tridentate ligand 2,2':6',2″-terpyridine (H-T), 4'-phenyl-2,2':6',2″-terpyridine (Ph-T), or 4'-pyrrolidin-N-yl-2,2':6',2″-terpyridine (pyrr-T). The presence of the pyrrolidinyl substituent imparts intraligand charge-transfer (ILCT) character to the ligand-based excited states and reduces the energy gap between the singlet and the triplet excited states. An enhanced rate of intersystem crossing results in a lutetium complex with a relatively small fluorescence quantum yield (0.15%) and a gadolinium complex with an impressive phosphorescence yield of 9.6% in deaerated solution. The Tb(pyrr-T)(NO3)3 system is unique because the relatively low-energy triplet ILCT state equilibrates with the emissive f-f state. The result is a truly remarkable f-f emission signal that is sensitive to the polarity of the local environment as well as the presence of dioxygen.

Azo-substituted Schiff base complex of Pt(II): Synthesis, characterization, DFT and TD-DFT study

The Pt(II) complex of N,N′-bis(5-phenylazosalicylidene) ethylenediamine was synthesized and characterized by IR and 1H NMR spectroscopies. TD-DFT calculations shows that the strong absorption at 397nm in the electronic spectra could be attributed to HOMO to LUMO transition a combination of MLCT, n to π* and intraligand charge transfer and the other strong absorption at 348nm is due to HOMO-1 to LUMO transition a combination of intraligand charge transfer, π to π* and n to π*.

Hydrogen Bond and Ligand Dissociation Dynamics in Fluoride Sensing of Re(I)-Polypyridyl Complex.

Hydrogen bonding interaction plays an essential role in the early phases of molecular recognition and colorimetric sensing of various anions in aprotic media. In this work, the host-guest interaction between fac-[Re(CO)3Cl(L)] with L = 4-([2,2'-bipyridin]-4-yl)phenol and fluoride ions is investigated for the hydrogen bond dynamics and the changing local coordination environment. The stoichiometric studies using (1)H NMR and ESI-MS spectroscopies have shown that proton transfer in the H-bonded phenol-fluoride complex activates the dissociation of the CO ligand in the Re(I) center. The phenol-to-phenolate conversion during formation of HF2(-) ion induces nucleophilic lability of the CO ligand which is probed by intraligand charge transfer (ILCT) and ligand-to-metal charge transfer (LMCT) transitions in transient absorption spectroscopy. After photoexcitation, phenol-phenoxide conversion rapidly equilibrates in 280 fs time scale and the ensuing excited state [Re(II)(bpy•(-)-phenolate¯) (CO)3Cl]* undergoes CO dissociation in the ultrafast time scale of ∼3 ps. A concerted mechanism of hydrogen cleavage and coordination change is established in anion sensing studies of the rhenium complex.

12-vertex ruthenacarborane half-sandwich complexes: Redox properties and second-order nonlinear optical responses

Carboranes are the chemist's toolbox, playing a crucial role in the development of the second-order nonlinear optical (NLO) materials. A series of 12-vertex ruthenacarborane half-sandwich complexes with the substituted 2,2′-bipyridyl and I ion ligands have been investigated by density functional theory (DFT). The calculated first hyperpolarizabilities (βtot) of the neutral complexes increase with replacing the –CO unite with electron donor 2,2′-bipyridyl and I ion. The redox processes of complex 3 significantly reduce βtot value. The oxidation process of complex 4 also reduce βtot value, while the reduced process enhance βtot value. Furthermore, the enhanced βtot values of the substituted systems are dominated by the intraligand charge transfer, ligand-to-metal charge transfer, metal-to-ligand charge transfer, and d–d transitions of Ru ion. Therefore, it can be concluded that different substituents and redox processes significantly influence the second-order NLO responses.

Redox-active ferrocene-dithiolenes hybrid complexes showing switchable nonlinear optical properties

Density functional theory(DFT) calculations were carried out to investigate the geometry structures, redox properties and second-order nonlinear optical(NLO) properties of ferrocene(Fc)-dithiolenes hybrid complexes. The switchable second-order NLO properties of these complexes are induced by the redox process. The oxidized process significantly affects the geometrical structures of the dithiolene moieties, that is, the embowed dithiolene moieties change into planar structures. It supports that the dithiolene moieties are the oxidized center. The βtot values of the cationic species are at least 4 and 10 times those of their corresponding parent complexes, respectively. Further, the time-dependent DFT calculation illustrates that the low-energy absorption(which is helpful for the large NLO response) is mainly assigned to intra-ligand charge transfer [π(ex-dithiolene)→π*(ex-dithiolene)]. These results suggest the potential use of the novel Fc-based dithiolenes complexes as versatile and fascinating NLO switching materials.