Synthesis and characterization of indole-containing chromophores for second-order nonlinear optics

Push-pull indole-containing nonlinear optical chromophores with different acceptor and pi-conjugated moieties have been synthesized and characterized. Experimental measurements of the second-order nonlinear optical response demonstrated that the chromophores exhibit similar or superior optical nonlinearity compared with their analogues with an aniline moiety as the donor group, but the indole-based chromophores display blue-shifted absorption, even up to 30 nm.     

Sulfur-capped cyclodextrins: a new class of cavitands with extroverted as well as introverted donor functionalities

Ansa-cyclodextrins were obtained in high yields by reaction of sodium sulfide with A,B-di- or A,B,D,E-tetramesylated alpha-CD precursors; the resulting thiocavitands are suitable for forming nanotubular molecules, as well as for hosting metal-organic fragments.     

Contrasting linear and quadratic nonlinear optical behavior of dipolar pyridinium chromophores with 4-(dimethylamino)phenyl or ruthenium(II) ammine electron donor groups

In this article, we contrast the optical properties of dipolar chromophores having 4-(dimethylamino)phenyl electron donor (D) and pyridinium acceptor (A) groups with those of closely related cations having pyridyl-coordinated Ru(II) donors. A range of physical data, including that from Stark (electroabsorption) spectroscopy, permits unprecedented quantitative comparisons, most notably regarding the effects of extension of bridging polyene chains. The purely organic compounds display normal optical properties in that their intense, visible pi --> pi intramolecular charge-transfer (ICT) bands red-shift as the number of E-ethylene units (n) increases from 1 to 3 and the associated static first hyperpolarizabilities beta(0) increase steadily with n. The related Ru(II) complexes show intense, visible d --> pi metal-to-ligand charge-transfer (MLCT) bands, which are found to lower energy when compared with the ICT transitions of the corresponding organics. Abnormally, these MLCT bands blue-shift as n increases, and beta(0) maximizes at n = 2. Time-dependent density-functional theory and finite field calculations verify these empirical trends for both types of compound, which can be rationalized as arising from the differing orbital structures of the chromophores and the associated degrees of D-A electronic coupling.     

Syntheses and characterization of ferrocenylthiocarboxylate-containing coordination compounds for nonlinear optics

Four metal-organic coordination compounds containing ferrocenylthiocarboxylate components, [Cd₂(η²-SOCFc)₂(η¹-μ₂-SOCFc)₂(4,4′-bpy)]_n (1), [Cd(SOCFc)₂(tmp)]_n (tmp = 4,4′-trimethylene-dipyridine) (2) [Zn(SOCFc)₂(2,2′-bpy)] (3), and {[Hg(SOCFc)₂(phen)] · (0.5CH₃OH)} (4) (Fc = (η⁵-C₅H₅)Fe(η⁵-C₅H₄)), have been prepared in search of good nonlinear optical (NLO) materials. Investigation of the NLO properties shows that Hg-containing compound 4 exhibits very strong third-order NLO absorptive and refractive effects. The NLO absorptive coefficient α₂ value (2.11 × 10⁻¹⁰ m W⁻¹) is larger than those of all the reported ferrocenylcarboxylate-containing coordination compounds and comparable to the well-performing Hg-containing complexes. Additionally, we further analyzed their NLO behaviors through studying electrochemical properties of the four compounds.     

Syntheses and crystal structures of four new organotin complexes with Schiff bases containing triazole

Four new organotin complexes, namely [(Bu₂Sn)₂O(EtO)(L1)]₂ (1), [(Bu₂Sn)₂O(EtO)(L2)]₂ (2), [(Bu₂Sn)₂O(EtO)(L3)]₂ (3) and [Ph₃Sn(L4)] · 0.5H₂O (4), were obtained by reactions of Bu₂SnO and Ph₃SnOH with 4-phenylideneamino-3-methyl-1,2,4-triazole-5-thione (HL1), 4-furfuralideneamino-3-methyl-1,2,4-triazole-5-thione (HL2), 4-(2-thienylideneamino)-3-ethyl-1,2,4 -triazole-5-thione (HL3) and 4-(3,5-di-t-butylsalicylideneamino)-3-ethyl-1,2,4-triazole-5-thione (HL4). Compounds 1-4 were characterized by elemental analysis, IR spectra and their structures were determined by single-crystal X-ray diffraction methods. Complexes 1-3 show similar structures containing a Sn₄O₄ ladder skeleton in which each of the exo tin atoms is bonded to the N atom of a corresponding thione-form deprotonated ligand. Complex 4 shows a mononuclear structure in which the tin atom of triphenyltin group is coordinated by the S atom of a thiol-form L4⁻ anion.     

Enhanced optoelectronic properties with aromatic bridges: A computational study on N-methyl pyridinium and phenolate types of push-pull zwitterions

A series of zwitterions with varying bridges, connecting N-methyl pyridinium acceptor, with phenolate donor, are investigated using various methodologies like, HF, B3LYP, CAM-B3LYP and ωB97xD. In this systematic study effects of various mono aromatic rings as bridges, on the response properties like, the dipole moments (μ), polarizabilities (α), hyperpolarizabilities (β) and adiabatic absorptions were analyzed using CPHF and TDDFT (or TDHF) theories. Compared to many traditional bridges, as well as without a bridge, enhanced nonlinear optical (2ND order NLO) responses were observed for these aromatically bridged zwitterions (with benzene ring as bridge ~5.3 times and ~7.9 times enhanced hyperpolarizabilities were observed compared to either the ethylene bridge or without any bridge cases, respectively). Also, many significant differences and large enhancements in response properties were observed compared to our earlier works on non-zwitterionic system (~4.3 times enhanced hyperpolarizability—benzene as bridge case). For some bridge cases, 10- to 15-fold enhanced hyperpolarizabilities were observed compared to without any bridge case. This work reports a class of non-TICT chromophores, promoting bridge aromaticity control on structure–property correlation, as a suitable and efficient chromophore design strategy to create a wide range of function molecular chromophores. Also, unidirectional natures of response properties and large dipole moments can make these zwitterions suitable 1D-molecular materials for various contemporary technological applications, as poled polymer-based materials.     

Synthesis and characterization of dicyanovinyl-substituted thienylpyrroles as new nonlinear optical chromophores

[structure: see text] New dicyanovinyl-substituted 1-(alkyl)aryl-2-(2'-thienyl)pyrroles 2 were synthesized and characterized. The solvatochromic behavior of the synthesized compounds was investigated. All the derivatives showed reversible oxidation and reduction on the CV time scale. The hyperpolarizabilities (beta) of compounds 2 were measured using hyper-Rayleigh scattering. The results are among the highest beta values reported for donor-acceptor-substituted thienylpyrroles.     

Syntheses and structures of four new mixed‐amide phosphoric triamides

Phosphoric triamides have extensive applications in biochemistry and are also used as O‐donor ligands. Four new mixed‐amide phosphoric triamide structures, namely rac‐N‐tert‐butyl‐N′,N′′‐dicyclohexyl‐N′′‐methylphosphoric triamide, C₁₇H₃₆N₃OP, (I), rac‐N,N′‐dicyclohexyl‐N′‐methyl‐N′′‐(p‐tolyl)phosphoric triamide, C₂₀H₃₄N₃OP, (II), N,N′,N′′‐tricyclohexyl‐N′′‐methylphosphoric triamide, C₁₉H₃₈N₃OP, (III), and 2‐[cyclohexyl(methyl)amino]‐5,5‐dimethyl‐1,3,2λ⁵‐diazaphosphinan‐2‐one, C₁₂H₂₆N₃OP, (IV), have been synthesized and studied by X‐ray diffraction and spectroscopic methods. Structures (I) and (II) are the first diffraction studies of acyclic racemic mixed‐amide phosphoric triamides. The P—N bonds resulting from the different substituent –N(CH₃)(C₆H₁₁), (C₆H₁₁)NH–, 4‐CH₃‐C₆H₄NH–, (tert‐C₄H₉)NH– and –NHCH₂C(CH₃)₂CH₂NH– groups are compared, along with the different molecular volumes and electron‐donor strengths. In all four structures, the molecules form extended chains through N—H…O hydrogen bonds.     

Some N-alkyl-naphthylazo pyridinium salts as new reagents for the spectrophotometric determination of anionic surfactants

Summary Eleven pyridinium azo dyes with straight-chain alkyl groups C_nH_2n+1–(n=6–18) and bromoalkyl groups BrC_mH_2m–(m=6–12) were synthesized with the intention of developing reagents for the determination of low levels of anionic surfactants in an aqueous medium. The effect of the alkyl chain length of these reagents on the reactivity with anionic surfactants such as sodium dodecylsulphate (SDS), sodium linear-dodecylbenzenesulphonate (DBS), sodium dodecylsulphonate (DS) and sodium laurate (SL) was studied. It was found that the alkyl chain length played an important role in the formation of ion associates and the composition of the ion associates formed. These reagents were classified into four groups with respect to the reactivity with anionic surfactants. The first group (n,m=6) reacts only with DBS. The second group (n,m=8) reacts with SDS, DBS and DS. The third group (n,m=10, 12) reacts with SDS, DBS and DS; however, the colour intensity of the DBS-ion associate was unstable. The fourth group (n=14, 16, 18) reacts with all anionic surfactants examined, and the composition of the ion associates with SDS and DS was 2:1 ([reagent]/[surfactant]) though that of the ion associates of the three reagent groups mentioned above was 1:1. The optimal conditions for the determination of anionic surfactants in river water with 1-octyl-4-(4-aminonaphthylazo)-pyridinium bromide was examined. The calibration graph was linear up to 3×10^–6 mol/l, and the apparent molar absorptivity of the ion associate was 3.8×10⁴ l mol^–1 cm^–1 (at 427 nm). The relative standard deviation for 2.4×10^–6 mol/l SDS was 4.9%. Recoveries of 88–107% were found for 8.0×10^–7 mol/l SDS in river water samples.     

Syntheses,Hirshfeld surface analyses,and luminescence of four new complexes

Four Cd-based complexes with chemical formulae [Cd(L¹)₂(2,2'-Bipy)(H₂O)] (I), [Cd(L²)₂(2,2'-Bipy) · 2H₂O] (II), [Cd(L¹)₂(Phen)(H₂O)] (III), {[Cd(L¹)₂(H₂O)(4,4'-Bipy)] · 3H₂O} (IV) (HL¹ = 3-(4-hydroxyphenyl)propanoic acid, HL² = p-hydroxyphenylacetic acid, Phen = phenantroline), have been synthesized and structurally characterized (CIF file CCDC nos. 1044844 (I), 1044844 (II), 1044844 (III), 1044847 (IV)). Single-crystal X-ray analyses reveal that compounds I and III have mononuclear Cd(II) units linking by three carboxylate groups, complex II shows dinuclear motif, whereas IV exhibits 1D chain constructed by bridging 4,4'-Bipy ligand. The assistant effect of chelating N-donor ligands with 2,2'-Bipy and Phen bind and bridging 4,4'-Bipy, as well as the flexibility of carboxylate, play an important to modulate on the resulting motifs. The detailed analyses of Hirshfeld surface and fingerprint plots provide insight into the nature of non-covalent interactions in the title compounds. Furthermore, the luminescent properties of the all compounds were discussed in detail.     

Synthesis and evaluation of new caged compound with thiochromone derivative

A new caged firefly luciferin (luciferin) with a thiochromone S,S-dioxide (TSSDO) as a photolabile protecting group was synthesized. Photodeprotection of the caged compound proceeded smoothly under photoirradiation at 365 nm in aqueous solution. The bioluminescence of the regenerated luciferin after uncaging was detected using a typical luciferin–luciferase reaction. These results indicated that TSSDO could be an attractive chemical tool for regulating biological phenomena.     

Syntheses, pi-stacking interactions and base-pairings of uracil pyridinium salts and uracilyl betaines with nucleobases

Reaction of 6-chlorouracil with 4-(dimethylamino)pyridine, 4-methylpyridine, and pyridin-4-yl-morpholine yielded pyridinium-substituted uracils as chlorides which were converted into pyridinium uracilates by deprotonation. These heterocyclic mesomeric betaines are cross-conjugated and thus possess separate cationic (pyridinium) and anionic (uracilate) moieties. Calculations and X-ray single crystal analyses were performed in order to characterize these systems and to compare the salts with the betaines. (1)H NMR experiments in D(2)O proved pi-interactions between the uracilyl betaines and adenine, adenosine, as well as adeninium. No pi-stacking interactions were detected between the betaines and guanosine. The acidic N8-H group of the uracil pyridinium salts caused acid-base reactions which were observed in parallel to pi-stacking interactions. Self-complementarity of the modified uracils was detected by (1)H NMR experiments in DMSO-d(6) and electrospray ionisation mass spectrometry (ESIMS). Ab initio calculations predicted base-pairings of the modified uracils with adeninium, cytosine, and guanine. Several geometries of hydrogen-bonded associates were calculated. Hoogsteen pairings between the uracil-4-(dimethylamino)pyridinium salt and adeninium, as well as associates between the corresponding betaine plus cytosine, and the betaine plus guanine were calculated, and the most stable conformations were determined. In the ESI mass spectra, prominent peaks of associates between the modified uracils and adeninium, cytosine, cytidine, guanosine and d(CpGp) were detected.     

Organometallic complexes for nonlinear optics: Part 21. Syntheses and quadratic hyperpolarizabilities of alkynyl complexes containing optically active 1,2-bis(methylphenylphosphino)benzene ligands

The preparation of the chloro complex trans-[FeCl₂{(R,R)-diph}₂] (1) and the alkynyl complexes trans-[M(4-CCC₆H₄R)Cl{(R,R)-diph}₂] [M=Fe, R=NO₂ (2); M=Ru, R=H (4), NO₂ (5), (E)-CH=CH-4-C₆H₄NO₂ (6); M=Os, R=NO₂ (7)], incorporating the optically active diphosphine 1,2-bis(methylphenylphosphino)benzene (diph), are described. Oxidation potentials, as determined by cyclic voltammetry, increase as 2<7<5. Molecular quadratic nonlinearities by hyper-Rayleigh scattering at 1064 nm increase upon introduction of an acceptor group (4<5), chain-lengthening of bridging group (5<6), and proceeding from 3d to 4d and 5d metal (2≤5≤7). Two-level-corrected nonlinearities reproduce the first two trends, but metal variation follows the sequence 2<7<5. The experimental and two-level-corrected nonlinearities for 6 (2795×10⁻³⁰ and 406×10⁻³⁰ esu, respectively), are amongst the largest observed thus far for organometallic complexes. Crystals of complexes 2 and 7 exhibit second-harmonic generation (assessed using the Kurtz powder technique), with an efficiency for the former of twice that of urea.     

Vibrational and quantum-chemical study of push-pull chromophores for second-order nonlinear optics from rigidified thiophene-based pi-conjugating spacers

Two types of push-pull chromophores built around thiophene-based pi-conjugating spacers rigidified by either covalent bonds or noncovalent intramolecular interactions have been analysed by means of IR and Raman spectroscopical measurements in the solid state as well as in a variety of solvents. Comparison of the Raman features of NLO-phores based on a covalently rigidified dithienylene (DTE) spacer with those of their open chain DTE analogues shows that the bridging of the central double bond of DTE with the nearest beta-positions of the thienyl units through two ethylene bridges significantly improves the intramolecular charge transfer. This also occurs for NLO-phores based on a 2,2'-bi(3,4-ethylenedioxythiophene) (BEDOT) spacer as compared with their corresponding parent compounds based on an unsubstituted bithiophene (BT) spacer. For NLO-phores based on a BEDOT spacer, noncovalent intramolecular interactions between sulfur and oxygen atoms are responsible for the rigidification of the spacer. The Raman spectra of these NLO-phores obtained in the form of solutes in dilute solutions reveal two different behaviours: i) chromophores based on covalently bridged or open chain DTE spacers display Raman spectral profiles in solution quite similar to those of the corresponding solids, with a very little dependence on the polarity of the solvent, while ii) larger spectral changes are noticed for NLO-phores built around BEDOT or BT spacers on going from solids to solutions. In the second case, spectral changes must be ascribed not solely to conformational distortions of the donor and acceptor end groups with respect to the pi-conjugated backbone mean-square-plane (as for the DTE-based NLO-phores) but also to distortions of the thienyl units of the pi-conjugating spacer from coplanarity. The insertion of vinylenic bridges between the thienyl units of the pi-conjugating spacer and between the spacer and the donor and acceptor end groups is a suitable strategy to reach a fairly large intramolecular charge transfer both in polar and nonpolar solvents. Density functional theory (DFT) calculations have been carried out to assign the relevant electronic and vibrational features and to derive useful information about the molecular structure of these NLO-phores.     

Probing the electronic structure of platinum(II) chromophores: crystal structures, NMR structures, and photophysical properties of six new bis- and di- phenolate/thiolate Pt(II)diimine chromophores

A general route for synthesis of six structurally similar Pt(II) diimine thiolate/phenolates chromophores possessing bulky phenolate or thiolate ligands is reported. The Pt chromophores were characterized using an array of techniques including 1H, 13C, and 195Pt NMR, absorption, emission, (spectro)electrochemistry, and EPR spectroscopy. Systematic variation of the electronic structure of the Pt(II) chromophores studied was achieved by (i) changing solvent polarity; (ii) substituting oxygen for sulfur in the donor ligand; (iii) alternating donor ligands from bis- to di-coordination; and (iv) changing the electron donating/withdrawing properties of the ligand(s). The lowest excited state in these new chromophores was assigned to a [charge-transfer-to-diimine] transition from the HOMO of mixed Pt/S (or Pt/O) character on the basis of absorption and emission spectroscopy, UV/vis (spectro)electrochemistry, and EPR spectroscopy. One of the chromophores, Pt(dpphen)(3,5-di-tert-butyl-catecholate) represents an example of a Pt(II) diimine phenolate chromophore that possesses a reversible oxidation centered predominantly on the donor ligand. Results from EPR spectroscopy indicate participation of the Pt(II) orbitals in the HOMO. There is a dramatic difference in the photophysical properties of carborane complexes compared to other mixed-ligand Pt(II) compounds, which includes room-temperature emission and photostability. The charge-transfer character of the lowest excited state in this series of chromophores is maintained throughout. Moreover, the absorption and emission energies and the redox properties of the excited state can be significantly tuned.     

Organometallic complexes for nonlinear optics. 41: Syntheses and quadratic NLO properties of 4-{4-(4-nitrophenyl)diazophenyl}ethynylphenylethynyl complexes

The syntheses of [Au(CC-4-C₆H₄CC-4-C₆H₄NN-4-C₆H₄NO₂)(PPh₃)] (3), trans-[Ru(CC-4-C₆H₄-CC-4-C₆H₄NN-4-C₆H₄NO₂)Cl(dppm)₂] (4), [Ru(CC-4-C₆H₄CC-4-C₆H₄NN-4-C₆H₄NO₂)(dppe)(η-C₅Me₅)] (5), and [Ni(CC-4-C₆H₄NN-4-C₆H₄NO₂)(PPh₃)(η-C₅H₅)] (6) are reported, together with a single-crystal X-ray diffraction study of 4. Quadratic nonlinearities for 3–6 and [Ru(CC-4-C₆H₄NO₂)(dppe)(η-C₅Me₅)] (7) have been determined at 1.064 μm and 1.300 μm by the hyper-Rayleigh scattering (HRS) technique, comparison to related complexes revealing that β values increase on introduction of azo group and π-system lengthening.     

Syntheses and crystal structures of four new fpa-metal complexes through in situ ligand reaction

Four new fpa-metal complexes, [Co(fpa)₂(H₂O)₂] (1), [Cu(fpa)₂(H₂O)] (2), [Zn₂(fpa)₄(bpp)₂] _n (3), and {[Zn(bpy)(H₂O)₄]?·?2(fpa)} _n (4), have been synthesized and fully characterized by elemental analyses, IR spectroscopy, single-crystal X-ray diffraction, and thermogravimetric analysis (TGA), (Hfpa?=?2,2-difluoro-2-(pyridine-2-yl)acetate, bpp?=?1,3-bis(4-pyridyl)propane, bpy?=?4,4′-bipyridine). X-ray diffraction analyses reveal that 1 and 2 with 0-D structures are both extended into 3-D supramolecular networks through hydrogen bonds and π···π interactions. Complex 3 with chiral centers possesses a 1-D structure constructed by two kinds of bpp molecules and four kinds of fpa^? molecules with different conformations, with bbp and fpa^? bridging and capped ligands, respectively. In 4, bpy links [Zn(H₂O)₄]²⁺ into a 1-D polymeric cationic chain and uncoordinated fpa^? compensates the framework charge. The results of TGA reveal that fpa^? decomposes through two processes. Both 3 and 4 show strong fluorescence in the solid state at room temperature.     

Design and synthesis of push-pull chromophores for second-order nonlinear optics derived from rigidified thiophene-based pi-conjugating spacers.

Two series of push-pull chromophores built around thiophene-based pi-conjugating spacers rigidified either by covalent bonds or by noncovalent intramolecular interactions have been synthesized and characterized by UV-vis spectroscopy, electric field induced second harmonic generation (EFISH) and differential scanning calorimetry. Comparison of the linear and second-order nonlinear optical properties of chromophores based on a covalently bridged dithienylethylene (DTE) spacer with those of their analogues based on open chain DTE shows that the rigidification of the spacer produces a considerable bathochromic shift of the absorption maximum together with a dramatic enhancement of the molecular quadratic hyperpolarizability (mu beta) which reaches values among the highest reported so far. A second series of NLO-phores has been derived from a 2,2'-bi(3,4-ethylenedioxythiophene) (BEDOT) pi-conjugating spacer. As indicated by X-ray and UV-vis data, rigidification of the spacer originates in that case, from noncovalent intramolecular interactions between sulfur and oxygen atoms. Again, comparison with the parent compounds based on an unsubstituted bithiophene spacer reveals a marked red shift of the absorption maximum and a large enhancement of mu beta. In an attempt to distinguish the contribution of the electronic and geometrical effects of the ethylenedioxy group, a third series of NLO-phores based on 3,4-ethylenedioxythiophene (EDOT) and 3,4-dihexyloxythiophene spacers has been synthesized. Comparison with compounds based on unsubstituted thiophene shows that, despite a red shift of lambda(max), introduction of alkoxy groups leads to a decrease of mu beta. Theoretical calculations indicate that this effect results from a decrease of the dipole moment (mu) caused by the auxiliary electron-donor alkoxy groups on the thiophene ring. In contrast, replacement of BT by BEDOT produces an increase of mu, which associated with the noncovalent rigidification of the BT system accounts for the observed enhancement of mu beta.     

Syntheses and luminescence of four supramolecular coordination complexes with flexible ligand

Four d ¹⁰-based complexes with chemical formulae {[Zn(L¹)₂(H₂O)₂(4,4′-Bipy)₂] (I), {[Zn₂(L¹)₄(Mi)] · 4H₂O} (II), {[Zn(L¹)₂(Phen)] · H₂O} (III) {[Cd(L¹)₂(Phen)] · 2H₂O} (IV) (HL¹ = p-hydroxy phenylacetic acid, 4,4′-Bipy = 4,4′-bipyridine, Phen = 1,10-phenanthroline, Mi = 1,4-bis(imidazol-1-yl)butane) have been synthesized and structurally characterized by single crystal X-ray diffraction (CIF files CCDC nos. 1047119 (I), 1047120 (II), 1047121 (III), 1047122 (IV)). The significant effect of assistant ligands and metal ions on assembly of I?IV has been demonstrated, which leads to the formation of distinct crystalline products. Complexes I?IV show various coordination motifs with different existing forms and coordination modes of the organic ligands. Furthermore, extend supramolecular networks are connected by secondary interactions such as hydrogen-bonding and aromatic stacking. The thermal stability and luminescent properties of the compounds were discussed in detail.     

Synthesis and characterization of new thienylpyrrolyl-benzothiazoles as efficient and thermally stable nonlinear optical chromophores

The synthesis and full characterization of new chromophores with second-order nonlinearities containing thienylpyrrolyl and benzothiazolyl moieties are reported. The solvatochromic behavior of the compounds was investigated. The hyperpolarizabilities β of derivatives 4-6 were measured using hyper-Rayleigh scattering and thermogravimetric analysis (TGA) was used to evaluate their thermal stability. The experimental results indicate that strong nonlinearity is balanced by good thermal stability especially for chromophores 6b and 6c, making them good candidates for NLO applications.