New Nonlinear Optical Chromophore: Synthesis, Structures, and Optical Limiting Effect of Transition-Metal Clusters (n-Bu4N)3[WM3Br4S4] (M = Cu and Ag)

Construction of cluster-based supramolecular wire and rectangle

Reactions of [Et₄N][Tp*WS₃(CuCl)₃] (1) (Tp* = hydridotris(3,5-dimethylpyrazol-1-yl)borate) with 2 equiv. of AgOTf (OTf^- = trifluoromethanesulfonate) and 1 equiv. of several bidentate pyridine ligands including 2,5-bis(pyridine-4-yl)thiazolo[5,4-d]thiazole (L1), 2,7-di(pyridin-4-yl)-9H-fluorene (L2), 2,7-di(pyridin-4-yl)-9H-carbazole (L3), and 2,7-di(pyridin-4-yl)-9H-fluoren-9-one (L4) afforded four W/Cu/S cluster-based supramolecular compounds [(Tp*WS₃Cu₂Cl)₂(L1)] (2), {[(Tp*WS₃Cu₃)₂(μ-Cl)₂(μ₄-Cl)]₂(L2)₂}(OTf)₂ (3), {[(Tp*WS₃Cu₃)₂(μ-Cl)₂(μ₄-Cl)]₂(L3)₂}(OTf)₂ (4) and {[(Tp*WS₃Cu₃)₂(μ-Cl)₂(μ4-Cl)]₂(L4)₂}(OTf)₂ (5). Compounds 2-5 were characterized by elemental analysis, IR, UV-vis, ¹H NMR, and single-crystal X-ray diffraction analysis. The neutral cluster 2 behaves as a supramolecular wire constructed by L1 bridging two butterfly-shaped [Tp*WS₃Cu₂Cl] cores. The cluster cations of 3-5 contain two [(Tp*WS₃Cu₃)₂(μ-Cl)₂(μ₄-Cl)]⁺ cores linked by two L2, L3, or L4 ligands, which finally formed a cationic supramolecular rectangle. The third-order nonlinear-optical (NLO) properties of 3-5 in DMF were also investigated by Z-scan techniques and their NLO responses were enhanced compared to those of their precursor 1.

Strong optical limiting properties of Ormosil gel glasses doped with silver nano-particles

Ag NP Ormosil gel glasses show good optical limiting performance with nonlinear optical response in the visible and NIR region.

Nonlinear Optical Materials for the Smart Filtering of Optical Radiation

The control of luminous radiation has extremely important implications for modern and future technologies as well as in medicine. In this Review, we detail chemical structures and their relevant photophysical features for various groups of materials, including organic dyes such as metalloporphyrins and metallophthalocyanines (and derivatives), other common organic materials, mixed metal complexes and clusters, fullerenes, dendrimeric nanocomposites, polymeric materials (organic and/or inorganic), inorganic semiconductors, and other nanoscopic materials, utilized or potentially useful for the realization of devices able to filter in a smart way an external radiation. The concept of smart is referred to the characteristic of those materials that are capable to filter the radiation in a dynamic way without the need of an ancillary system for the activation of the required transmission change. In particular, this Review gives emphasis to the nonlinear optical properties of photoactive materials for the function of optical power limiting. All known mechanisms of optical limiting have been analyzed and discussed for the different types of materials.

Synthesis and optical power limiting properties of heteroleptic Mo3S7 clusters

Substitution of the halide ligands in (Bu4N)2[Mo3S7X6] (X = Cl, Br) by diimine ligands, such as 4,4'-dimethyl-2,2'-bipyridine (dmbpy), 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen), affords the neutral heteroleptic clusters Mo3S7Cl4(dmbpy) (), Mo3S7Br4(dmbpy) (), Mo3S7Br4(bpy) (), and Mo3S7Br4(phen) (). Further substitution of the halide ligands in Mo3S7Br4(diimine) clusters by dmit (1,3-dithiole-2-thione-4,5-dithiolate) allows the preparation of the mixed diimine-dithiolene neutral cluster complexes Mo3S7(dnbpy)(dmit)2 (, dnbpy = 4,4'-dinonyl-2,2'-bipyridine), Mo3S7(dcmbpy)(dmit)2 (, dcmbpy = 4,4'-dimethoxycarbonyl-2,2'-bipyridine), and Mo3S7(dcbpy)(dmit)2 (, dcbpy = 2,2'-bipyridine-4,4'-dicarboxylic acid). The optical limiting properties of complexes have been assessed by the open-aperture Z-scan technique at 570 nm, employing a nanosecond optical parametric oscillator. In order to investigate the effect of increasing the π-system, complexes , with the general formula Mo3S7X4(diimine), (X = Cl, Br), were compared to clusters , containing the dmit ligand. The influence of the metal content on the optical power limiting properties was also investigated by comparing the trinuclear series of complexes prepared herein with the bis(dithiolene) dinuclear cluster (Et4N)2[Mo2O2S2(BPyDTS2)2], which has been recently prepared by our group. All trinuclear clusters are efficient optical limiters (σeff > σ0) with the threshold limiting fluence F15% decreasing on proceeding from dinuclear to trinuclear clusters and, generally, on extending the π-system.

Organometallic acetylides of Pt(II), Au(I) and Hg(II) as new generation optical power limiting materials

Within the scope of nonlinear optics, optical power limiting (OPL) materials are commonly regarded as an important class of compounds which can protect the delicate optical sensors or human eyes from sudden exposure to damaging intense laser beams. Recent efforts have been devoted to developing organometallic acetylide complexes, dendrimers and polymers as high performance OPL materials of the next generation which can favorably optimize the optical limiting/transparency trade-off issue. These metallated materials offer a new avenue towards a new family of highly transparent homo- and heterometallic optical limiters with good solution processability which outperform those of current state-of-the-art visible-light-absorbing competitors such as fullerenes, metalloporphyrins and metallophthalocyanines. This critical review aims to provide a detailed account on the recent advances of these novel OPL chromophores. Their OPL activity was shown to depend strongly on the electronic characters of the aryleneethynylene ligand and transition metal moieties as well as the conjugation chain length of the compounds. Strategies including copolymerization with other transition metals, change of structural geometry, use of a dendritic platform and variation of the type and content of transition metal ions would strongly govern their photophysical behavior and improve the resulting OPL responses. Special emphasis is placed on the structure-OPL response relationships of these organometallic acetylide materials. The research endeavors for realizing practical OPL devices based on these materials have also been presented. This article concludes with perspectives on the current status of the field, as well as opportunities that lie just beyond its frontier (106 references).

Excited State Absorption Dynamics in Metal Cluster Polymer [WS4Cu3I(4-bpy)3]n Solution

The nonlinear absorptive property of a novel metal cluster [WS(4)Cu(3)I(4-bpy)3]n in DMF solution is studied by using an open-aperture Z-scan technique with picosecond and nanosecond laser pulses at the wavelength of 532 nm. The experimental results show that the cluster has strong nonlinear absorption under the 8 ns pulse excitation and a relatively weak nonlinear absorptive property under the picosecond pulse excitation. The picosecond pump-probe response of the metal cluster is similar to that of C60 solution, which implies that the nonlinear mechanisms are the same for the two materials. By using the rate-equation model, the experimental data are theoretically simulated; several optical parameters of the cluster, especially the lifetime of the higher excited singlet state of the cluster, are obtained.

Axial Halogen Ligand Effect on Photophysics and Optical Power Limiting of Some Indium Naphthalocyanines

Three axially substituted complexes, 2,3-octa(3,5-di-tert-butylphenoxy)-2,3-naphthalocyaninato indium chloride (1a), 2,3-octa(3,5-di-tert-butylphenoxy)-2,3-naphthalocyaninato indium bromide (1b), and 2,3-octa(3,5-di-tert-butylphenoxy)-2,3-naphthalocyaninato indium iodide (1c) have been synthesized and their photophysical properties have been investigated. Optical power limiting of nanosecond (ns) and picosecond (ps) laser pulses at 532 nm using these complexes has been demonstrated. All complexes display strong Q(0,0) absorption and measurable emission in the near-infrared region and exhibit strong excited-state absorption in the range of 470-700 nm upon ns laser excitation. The different axial ligands show negligible effect on the linear absorption, emission, and transient difference absorption spectra. However, the excited-state lifetime, triplet excited-state quantum yield, and efficiency to generate singlet oxygen are affected significantly by the heavier axial ligand. Brominated and iodinated complexes 1b and 1c show higher triplet excited-state quantum yield, while chlorinated complex 1a has longer excited-state lifetime and is more efficient in generating singlet oxygen. The iodinated complex 1c displayed the best optical limiting due to the higher ratio of excited-state absorption cross section to ground state absorption cross section (sigma(eff)/sigma(0)).

Construction of New Heteroselenometallic Clusters: Formation of Crownlike [Et4N]4[(μ5-WSe4)(CuI)5(μ-I)2] and Octahedral Polymeric [(μ6-WSe4)Cu6I4(py)4]n from Planar [Et4N]4[(μ4-WSe4)Cu4I6] with Additional Faces

The coplanar cluster compound [Et4N]4[(mu4-WSe4)Cu4I6] (1) was prepared from reaction of [Et4N]2[WSe4] with 4 equiv of CuI in N,N-dimethylformamide (DMF) solution in the presence of [Et(4)N]I. Treatment of 1 with pyridine (py) in dry MeCN gave the neutral cluster [(mu4-WSe4)Cu4(py)6I2] (2) in good yield. Recrystallization of 1 from py/i-PrOH resulted in the reorganization of the coplanar WSe4Cu4 core and the formation of a neutral polymeric cluster [(mu3-WOSe3)Cu3(py)3(mu-I)]n (3) containing a nest-shaped OWSe3Cu3 core and a terminal W=O bond. The interaction of cluster 1 with excess PPh3 in CH3Cl3 gave [(mu3-WSe4)Cu3(PPh3)3(mu3-I)] (4) which has a cubanelike SeWSe3Cu3I core. Treatment of 1 with 1 equiv of CuI in dimethyl sulfoxide (DMSO) yielded [Et4N]4[(mu5-WSe4)(CuI)5(mu-I)2] (5) which has a crown-like core structure. Treatment of 1 in DMF with 2 equiv of CuI in the presence of py resulted in the formation of a two-dimensional polymeric cluster, [(mu6-WSe4)Cu6I4(py)4]n (6), consisting of an octahedral WSe4Cu6 repeating unit. The solid-state structures of clusters 3, 5, and 6 have been further established by X-ray crystallography. The nonlinear optical properties of 6 have been also investigated. Cluster 6 was found to exhibit good photostability and a large optical limiting effect with the limiting threshold being ca. 0.3 J cm(-2).

Electronic structures and nonlinear optical properties of trinuclear transition metal clusters M-(mu-S)-M' (M = Mo, W; M' = Cu, Ag, Au)

A series of trinuclear metal clusters MS4(M'PPh3)2(M'PPh3) (M = Mo, W; M' = Cu, Ag, Au) have been studied using the density functional theory (DFT) method. The static polarizabilities and hyperpolarizabilities of the model clusters have been calculated using the finite-field (F-F) method. The model clusters, divided into two groups, are alike in the structure of two fragments of rhombic units M-(mu-S)2-M' (M = Mo, W; M' = Cu, Ag, Au), perpendicular to each other, which are joined by sharing the bridge metal M. It is the charge transfer from one of these moieties to the other in these characteristic sulfido-transitional metal cores that is responsible for the polarizabilities and hyperpolarizabilities. This kind of electronic delocalization, different from that of the planar pi-system, is interesting and warrants further investigation. The structural effects on properties are important. In these models, considerable third-order nonlinearities are exhibited. The element substitution effect of Mo and W is weak, while that of Cu and Ag is relatively substantial. An overall order is gamma xxxx(Mo-Ag) > gamma xxxx(W-Ag) > gamma xxxx(Mo-Au) > gamma xxxx(W-Au) > gamma xxxx (Mo-Cu) > gamma xxxx(W-Cu) and gamma av(Mo-Ag) approximately gamma av(W-Ag) > gamma av(Mo-Au) approximately gamma av(W-Au) approximately gamma av (Mo-Cu) approximately gamma av(W-Cu).