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An emerging field regarding N^C^N terdentate Pt(ii) complexes is their application as luminescent labels for bio-imaging. In fact, phosphorescent Pt complexes possess many advantages such as a wide emission color tunability, a better stability towards photo- and chemical degradation, a very large Stokes shift, and long-lived luminescent excited states with lifetimes typically two to three orders of magnitude longer than those of classic organic fluorophores. Here, we describe the synthesis and photophysical characterization of three new neutral N^C^N terdentate cyclometallated Pt complexes as long-lived bio-imaging probes. The novel molecular probes bear hydrophilic (oligo-)ethyleneglycol chains of various lengths to increase their water solubility and bio-compatibility and to impart amphiphilic nature to the molecules. The complexes are characterized by a high cell permeability and a low cytotoxicity, with an internalization kinetics that depends on both the length of the ethyleneglycol chain and the ancillary ligand. [ABSTRACT FROM AUTHOR]

An unprecedented DTE-based Pt(ii) complex, 2(o), which stands as the first example of a sequential double nonlinear optical switch, induced first by protonation and next upon irradiation with UV light is presented. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cyclometallated N^C^N -Pt(II) complexes have excellent photophysical features for bio-imaging and photodynamic therapy. • N^C^N -Pt(II) complexes offer a powerful tool for real-time oxygen mapping and for differentiation within the cell. • Combination with time-resolved techniques allows imaging via autofluorescence background and short-lived species cut-off. • Good two-photon absorption cross-sections of Pt(II) complexes allow two-photon excitation with red or NIR light. • N^C^N -Pt(II) complexes are able to kill various types of cancer cells in the presence of a suitable radiation. In 1999, the first platinum(II) complex bearing a cyclometalated 1,3-di(2-pyridyl)benzene ligand was prepared. Since then, a lot of work has been devoted to the preparation and characterization of new members of this family, and to their use for application in photonics, optoelectronics and medicinal chemistry. The present review is an excursion on their great potential for bio-imaging and photodynamic therapy. In the introduction, the advantages of heavy metal-containing compounds as luminescent probes will be briefly given together with the important features of cyclometalated Pt(II) complexes with a 1,3-bis(pyridin-2-yl)benzene scaffold. Then, the studies carried out up to now with this fascinating Pt(II) family in bio-imaging and photodynamic therapy will be illustrated. The aim of this review is to show their high potential for high resolution bio-imaging and light-activated cancer treatments. [ABSTRACT FROM AUTHOR]

Novel photochromic dithienylethene-based platinum(ll) complexes (C∧N∧N)Pt(C≡C-DTE-C6H4-D) ((C∧N∧N) = 4,4'-di(n-hexyl)-6-phenyl-2,2'-bipyridine; D = H, NMe2) were prepared and characterized. Their excellent photochromic properties allow the photoinduced switching of their second-order nonlinear optical properties in solution, as measured by the EFISH technique, due to formation of an extended π -conjugated ligand upon suitable electromagnetic radiation. Insights into the electronic structures of the complexes and the nature of their excited states have been obtained by DFT and TD-DFT calculations. These novel Pt(II) complexes were nanoorganized in polymer films which were poled, affording new materials characterized by a good second-order NLO response that can be easily switched, with an excellent NLO contrast. To the best of our knowledge, our compounds allowed designing the very first examples of switchable NLO polymer films based on metal complexes. [ABSTRACT FROM AUTHOR]

Abstract: We studied the second-order NLO properties in solution of various Ir(III) acetylacetonate complexes bearing a substituted cyclometallated 4-styryl-2-phenylpyridine (ppy-4-styryl-R, with R = NEt2, OMe, H, NO2) with the EFISH technique. The dipole moments were evaluated by Density Functional Theory (DFT) calculations. We have also investigated the Second Harmonic Generation (SHG) of composite films based on the various cyclometallated Ir(III) complexes dispersed and oriented in a polymethylmethacrylate (PMMA) matrix. [Copyright &y& Elsevier]

Highlights: [•] Two ruthenium oxyquinolate complexes for DSSCs were prepared. [•] Microwave reactor allowed drastic reduction of reaction time and higher selectivity. [•] Electrochemical and photovoltaic characterizations were performed. [ABSTRACT FROM AUTHOR]

Appropriate functionalization of the cyclometalated ligand, L, and the choice of the ancillary ligand, X, allows the dipolar second-order nonlinear optical response of luminescent [Pt LX] complexes-in which L is an N^C^N-coordinated 1,3-di(2-pyridyl)benzene ligand and X is a monodentate halide or acetylide ligand-to be controlled. The complementary use of electric-field-induced second-harmonic (EFISH) generation and harmonic light scattering (HLS) measurements demonstrates how the quadratic hyperpolarizability of this appealing family of multifunctional chromophores, characterized by a good transparency throughout much of the visible region, is dominated by an octupolar contribution. [ABSTRACT FROM AUTHOR]

The synthesis, luminescence, and nonlinear optical properties of a new series of Ir(ppy)3 (ppy = 2-phenylpyridine) complexes incorporating π-extended vinyl-aryl substituents at the para positions of their pyridine rings are reported. Appropriate substitution of the pyridyl rings allows the tuning of the luminescence properties and the second-order nonlinear optical response of this unusual family of three-dimensional chromophores. Theoretical calculations were performed to evaluate the dipole moments, to gain insight into the electronic structure, and to rationalize the observed optical properties of the investigated complexes. [ABSTRACT FROM AUTHOR]

The trinuclear [Ln(NO3)3 (CuL) 2] complexes (Ln = La, Ce, Sm, Eu and Er, L = N,N'-l,3-propylen-bis(salicylideniminato) have been investigated by a combination of HLS and EFISH techniques to evaluate both the dipolar and octupolar contributions to their significant quadratic hyperpolarizability and to confirm that f electrons may tune their second-order NLO response, hi the complexes investigated, the major contribution to the total quadratic hyperpolarizability is largely controlled by the octupolar contribution, but the values of both βEFISH and ǁ β1=1ǁ, that is the dipolar part, are significantly influenced by the number of f electrons, confirming that the unexpected polarizable character of f electrons may be the origin of such fascinating evidence. [ABSTRACT FROM AUTHOR]

Abstract: A new thiocyanate-free cyclometallated 2-phenylpyridine Ru(II) complex, [Ru(dFppyCF3)(dcbpy)2]+PF6 − (dFppyCF3 = 2-(2,4-difluorophenyl)-5-trifluoromethyilpyridine; dcbpy = 2,2′-bipyridine-4,4′-dicarboxylic acid), containing an electronwithdrawing trifluoromethyl group on the pyridine ring of the cyclometallated ligand, was synthesized and used as photosensitizer in DSSC devices. Its optical and electrochemical properties and stability behaviour towards ligand exchange with the common solar cell additive 4-tert-butylpyridine was compared to that of benchmark DSSC dye N719 and of the reference complex [Ru(dFppy)(dcbpy)2]+PF6 −. Substitution of the pyridine ring by the CF3 group afforded enhanced optical properties and a larger overall power conversion efficiency of the corresponding DSSC (3.7%), with a significant improvement compared to the reference cyclometallated complex under the same fabrication conditions. [Copyright &y& Elsevier]

A luminescent bis(salicylaldiminato)zinc(II) Schiff-base complex, 1, is characterized by a concentration dependent second-order nonlinear optical response, related to the degree of aggregation of the complex in a dichloromethane solution. The formation of the monomeric adduct, by addition of a Lewis base, such as pyridine, to concentrated solutions of 1, leads to a switch-on of the quadratic hyperpolarizability. This represents an unprecedented mode of NLO switching in molecular materials. [ABSTRACT FROM AUTHOR]

A series of cationic Ir(III) substituted bipyridyl (NN (NN-bpy) complexes incorporating electron-donor and -acceptor substituents, [Ir(CN-ppy-R′)2(NN-bpy-CH═CH-C6H4-R)][X] (X- = PF6- or C12H25SO3-), 2 (a, R = NEt2 and R′ = Me; b, R = O-Oct and R′ = Me; c, R = NO2 and R′ = C6H13; CN-ppy = cyclometalated 2-phenylpyridine, [Ir(CN-ppy-Me)2(NN-bpy-CH═CH-thienyl-Me)][PF6], 2d, and the dithienylethene (DTE)-containing complex 2e have been synthesized and characterized, and their absorption, luminescence, and quadratic nonlinear optical (NLO) properties are reported. Density functional theory (DFT) and time-dependent-DFT (TD-DFT) calculations on the complexes facilitate a detailed assignment of the excited states involved in the absorption and emission processes. All five complexes are luminescent in a rigid glass at 77 K, displaying vibronically structured spectra with long lifetimes (14-90 μs), attributed to triplet states localized on the styryl-appended bipyridines. The second-order NLO properties of 2a-d and related complexes 1a-d with 1,10-phenanthrolines have been investigated by both electric field induced second harmonic generation (EFISH) and harmonic light scattering (HLS) techniques. They are characterized by high negative EFISH μβ values which decrease when the ion pair strength between the cation and the counterion (PF6-, C12H25SO3-) increases. The EFISH response is mainly controlled by metal-to-ligand charge-transfer/ligand-to-ligand charge-transfer (MLCT/L′LCT) processes. A combination of HLS and EFISH techniques is used to evaluate both the dipolar and octupolar contributions to the total quadratic hyperpolarizability, demonstrating that the major contribution is controlled by the octupolar part. The incorporation of a photochromic DTE unit into the NN-bpy ligand (complex 2e) allows the luminescence to be switched ON or OFF. The photocyclisation of the DTE unit can be triggered by using either UV (365 nm) or visible light (430 nm), leading to an efficient quenching of the ligand-based 77 K luminescence, which can be restored upon irradiation of the closed form at 715 nm. In contrast, no significant modification of the EFISH μβ value is observed upon photocyclization, suggesting that the quadratic NLO response is dominated by the MLCT/L′LCT processes, rather than by the intraligand excited states localized on the substituted bipyridine ligand. [ABSTRACT FROM AUTHOR]

The second-order nonlinear optical (NLO) properties of [Ln(hfac)3(diglyme)] (hfac = hexafluo- roacetylacetonate; diglyme = bis(2-methoxyethyl)ether; Ln = La, Ce, Pr, Sm, Eu, Gd, Er, Lu) complexes have been investigated by a combination of electric-field second harmonic generation (EFISH) and harmonic light scattering (HLS) techniques, providing evidence for the relevant role of I electrons in tuning the second- order NLO response dominated by the octupolar contribution. These lanthanide NLO chromophores allow a clean valuation of the influence of f electrons on the quadratic hyperpolarizability and on its dipolar and octupolar contributions. Molecular quadratic hyperpolarizability values measured by the EFISH method, βEFISH, initially increase rapidly with the number of f electrons, the value for the Gd complex being 11 times that of the La complex, whereas this increase is much lower for the last seven f electrons, the βEFISH value of the Lu complex being only 1.2 times that of the Gd complex. The increase of (βHLS), which is dominated by an octupolar contribution, is much lower along the Ln series. Remarkably, the good (βHLS) values of these simple systems, well known for their luminescence properties, are reached at no cost of transparency. [ABSTRACT FROM AUTHOR]

Abstract: The anionic rhodium carbonyl clusters [Rh7(CO)16]3− and [Rh14(CO)25]4− can be easily prepared by a new simple and high yield one-pot synthesis starting from RhCl3·nH2O dissolved in ethylene glycol and involving two steps: (i) treatment of RhCl3·nH2O under 1atm of CO at 50°C to give [Rh(CO)2Cl2]−; (ii) addition of a base (CH3CO2Na or Na2CO3) followed by reductive carbonylation under 1atm of CO at an adequate temperature (50°C for [Rh7(CO)16]3−; 150°C for [Rh14(CO)25]4−). These new syntheses are more convenient than those previously reported, especially since such clusters are not accessible via silica surface-mediated reactions. This different behavior is due to the particular stabilization on the silica surface and under 1atm of CO of an anionic carbonyl cluster, called A, which does not allow the formation of a higher nuclearity carbonyl cluster, called B, which was shown to be the key-intermediate in the synthesis of [Rh14(CO)25]4− working in ethylene glycol solution. Although it was not possible to isolate crystals of A and B suitable for X-ray structural determination, a combination of cyclovoltammetry, one of the few examples so far available of the use of this technique for anionic rhodium carbonyl clusters, infrared spectroscopy and elemental analyses suggest that A and B are probably the never reported [Rh7(CO)14]− and [Rh15(CO)28]3− clusters, respectively. In particular the tentative formulation of the two clusters was carried out by a non-conventional method based on the existence of a linear correlation between carbonyl frequencies of the main band and the [(charge/Rh atoms)/CO number] ratio. [Copyright &y& Elsevier]

Abstract: The two-photon absorption (TPA) properties of 4,4′-bis(para-di-n-butylaminostyryl)-2,2′-bipyridine (NBu2bipy) and related dipolar ([ZnY2(NBu2bipy)] (Y=Cl, CF3CO2), [Zn(2,2′-bipyridine)2(NBu2bipy)][PF6]2) and octupolar ([Zn(NBu2bipy)3][PF6]2) complexes were investigated by the two-photon emission (TPE) technique in a femtosecond regime, working in the 730–930nm spectral range. We found, in contrast with previous literature data, that the TPA enhancement upon coordination of a TPA active ligand to a metal center may be larger in the dipolar rather than the corresponding octupolar complex, the response being easily modulated by the choice of the ancillary ligands. [Copyright &y& Elsevier]

Abstract: An original and convenient three steps (swelling–poling–deswelling) process of poling a cross-linked polymer/NLO-phore composite to produce a stable second harmonic generation is described, using as a model system a cross-linked poly-amido amine network carrying covalently attached a modified Disperse Red One, a well known NLO-phore. This procedure is expected to be of wide applicability to produce composite polymeric materials with a rather stable second harmonic generation and of particular interest for NLO-phores sensitive to temperature. [Copyright &y& Elsevier]

To evidentiate the role of the nature of sulfonate ancillary ligands on the value of the quadratic hyperpolarizability of Zn(II) complexes with stilbazole-like ligands, the second-order nonlinear optical (NLO) properties of [ZnY2(4,4'-trans-NC5H4CH=CHC6H4NMe2)2] complexes (Y = CF3SO3, CH3SO3, or p-CH3C6H4SO3) are investigated. By working at relatively high concentrations (>3 × 10-4 M), the positive effect of the triflate ligand remains unique while, with nonfluorinated sulfonate ligands, the second-order NLO response is comparable to that of the related complexes with acetate or trifluoroacetate as ancillary ligands. However, at dilutions higher than 10-4 M, all of the sulfonate complexes reach huge quadratic hyperpolarizabilities because of solvolysis with the formation of cationic species such as [ZnY(4,4'-trans-NC5H4CH=CHC6H4NMe2)2]+, characterized by a large second-order NLO response. This view is supported by careful conductivity measurements. The same behavior occurs if 4,4'-trans-NC5H4CH=CHC6H4NMe2 is substituted by 4,4'-trans, trans-NC5H4(CH=CH)2C6H4NMe2. [ABSTRACT FROM AUTHOR]

The hydrides localisation in the hydrido carbonyl cluster [H5Os10(CO)24]−, obtained in excellent and reproducible yields by hydrogenation (1 atm, 200 °C) of silica-supported [Os(CO)3(OH)2]n, has been investigated by variable temperature 1H NMR and X-ray diffraction of the [(Ph3P)2N]+ salt. Using both stereochemical and potential energy considerations, three μ2-H and two μ3-H have been localised in sites strictly related to those of the parent [H4Os10(CO)24]2− anion, where hydrides location had been obtained by neutron diffraction of the corresponding [(Ph3P)2N]+ salt. Such locations are in agreement with low temperature 1H NMR findings. Variable temperature 1H NMR investigation has also shown that μ2- and μ3-hydrides have a very different mobility. While μ2-hydrides exchange easily by an edge-shift process, their exchange with μ3-hydrides is much more difficult, as the exchange between μ3-hydrides themselves. [Copyright &y& Elsevier]

[Ru3(CO)12], [H4Ru4(CO)12], and [Ru6C(CO)16]2− have been synthesized in reproducible high yields and under mild conditions (1 atm) by a two-step methodology involving (i) first carbonylation of RuCl3·nH2O dissolved in ethylene glycol to give a mixture of tri- and di-carbonyl ruthenium(II) species, probably of the kind [Ru(CO)3Cl2(ethylene glycol)] and [Ru(CO)2Cl2(ethylene glycol)x] (x=1, 2), and (ii) addition of specific amounts of alkali carbonates and further reductive carbonylation to give the desired ruthenium carbonyl cluster. The selectivity of the second step is controlled by the: (i) nature and quantity of the alkali carbonate (Na2CO3 or K2CO3); (ii) gas-phase composition (CO or CO+H2); (iii) temperature. [Copyright &y& Elsevier]

[Display omitted] • In the coupling reaction of CO 2 and cyclohexene oxide, the catalytic activity of zinc complexes can be easily tuned. • Triflate ancillary ligands can turn on the catalytic activity of zinc complexes bearing a chelating nitrogen donor ligand. • Zinc complexes bearing triflates can be good catalysts for the ring-expansive carboxylation of cyclohexene oxide with CO 2. The catalytic activity of various zinc(II) complexes bearing a chelating nitrogen-donor ligand and different ancillary ligands (Cl, acetate, triflate) is investigated for the solvent-free coupling reaction of cyclohexene oxide and CO 2. The effect of a co-catalyst is also studied. Whereas the investigated zinc(II) complexes with chloride or acetate as ancillary ligand are inactive, those with triflate are active, allowing the selective formation of polyether or cyclic carbonate controlled by the presence of a suitable amount of [PPN]Cl. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel complex, [Pt(5-mesityl-1,3-di(2-pyridyl)benzene)(thioacetate)], has been prepared and fully characterised. • The luminescence quantum yield of [Pt(5-mesityl-1,3-di(2-pyridyl)benzene)(thioacetate)] is lower than that of related complexes with chloride or 1-phenyl-1 H -tetrazole-5-thiolate but higher than that with arylthionates. • In Pt(II) complexes bearing a cyclometalated 1,3-di(2-pyridyl)benzene, the effect of thiolates co-ligands is really intriguing and merits further investigations. Substitution of the chlorido ligand of the fascinating cyclometalated complex [Pt(5-mesityl-1,3-di(2-pyridyl)benzene)Cl] by thioacetate leads to the related thiolato complex [Pt(5-mesityl-1,3-di(2-pyridyl)benzene)(thioacetate)], which has been fully characterised. Its photophysical properties were determined in degassed dichloromethane solution, as blend in Poly(MethylMethAcrylate) (PMMA) thin films, and as powders, at room temperature. Both in solution and in thin films, an increase of the concentration of the complex leads to a red shift of the phosphorescence spectra and to a decrease of lifetime decays and quantum yield. It appears that tuning of emission spectra depends on the competition between monomeric and aggregate emissive states. No clear evidence of excimer formation has been detected. In powders, an aggregate emission spectrum is red-shifted at 602 nm, reaching a very low phosphorescence quantum yield of 1 %. [ABSTRACT FROM AUTHOR]

Three decades ago, dye-sensitized solar cells (DSSCs) emerged as a method for harnessing the energy of the sun and for converting it into electricity. Since then, a lot of work has been devoted to create better global photovoltaic efficiencies and long term stability. Among photosensitizers for DSSCs, thiocyanate-free ruthenium(II) complexes have gained increasing interest due to their better stability compared to conventional thiocyanate-based complexes, such as benchmark dyes N719 and Z907. In this mini-review, two classes of thiocyanate-free Ru(II) complexes are presented: (a) bis-bipyridyl compounds bearing an ancillary cyclometalating bidentate ligand; (b) bipyridyl compounds bearing non-cyclometalating ancillary ligands. The coverage, mainly from 2014 up to now, is not exhaustive, but illustrates the most recent design strategies and photovoltaic properties of these two families of ruthenium(II) dyes. [ABSTRACT FROM AUTHOR]

• Platinum compounds are very attractive for second-order nonlinear optics (NLO). • Well-designed platinum compounds can present a large quadratic hyperpolarizability. • The NLO response of complexes can be redox- or photo-modulated. Electrooptical devices and optical communications need compounds with second-order nonlinear optical (NLO) properties as construction blocks. Typically, to show a large quadratic hyperpolarizability, a compound should be asymmetric, be characterized by a large variation between the dipole moments in the excited and ground states, and have low energy electronic transitions. For example, a large quadratic hyperpolarizability can be reached when an electron-donor moiety is linked by means of a π-conjugated spacer to an acceptor group. In the field of second-order nonlinear optics, particularly attractive are coordination metal complexes because they are often characterized by low-energy and high-intensity intraligand (IL), ligand-to-metal (LM), and metal-to-ligand (ML) charge transfer (CT) electronic transitions, that can be regulated by the choice of the metal and ligands. Among them, platinum(II) complexes are captivating. During this excursion, we will see the quadratic hyperpolarizability of many of them. After some basic NLO notions, the review presents various classes of NLO-active platinum compounds having mono- and bidentate nitrogen ligands (pyridine, bipyridine, phenanthroline), dithiolenes, cyclometalated ligands (imines, phenylpyridine, phenylbipyridine, and dipyridylbenzene), alkynyl ligands. It is shown how to regulate the quadratic hyperpolarizability with suitable ligands and how to photomodulate the NLO properties by means of a dithienylethene (DTE) moiety. Some examples of complexes with redox-switchable NLO properties are also given. Although the accent is on the quadratic hyperpolarizability measured in solution, it is also shown how some NLO-active platinum complexes can be nano-organized to afford thin films with nonlinear optical properties. The report is not comprehensive, but it allows to get into the field of NLO-active platinum compounds and to understand their potential. [ABSTRACT FROM AUTHOR]

Diphenyl-(4-{2-[4-(2-pyridin-4-yl-vinyl)-phenyl]-vinyl}-phenyl)-amine (DPVPA) constitutes a novel acido-triggered reversible luminescent and nonlinear optical switch. Remarkably, for the first time the Electric-Field Induced Second Harmonic generation (EFISH) technique is used to reveal a protonation-deprotonation NLO contrast. [ABSTRACT FROM AUTHOR]

The synthesis of the new complex [Ru-(Tetrazpy)(dcbpy)2]CI is reported, along with its spectroscopical, electrochemical, and theoretical character-ization. The first dye-sensitized solar cell device with this complex has been prepared, leading to a 3% of conversion efficiency, promising data considering the simplicity of the Tetrazpy ligand. [ABSTRACT FROM AUTHOR]

• The versatile properties of iridium complexes make them appealing for nonlinear optics (NLO). • Iridium complexes with suitable ligands have interesting second-order NLO properties. • Iridium complexes with suitable ligands have interesting two-photon absorption properties. Molecules with second-order nonlinear optical (NLO) properties have received a lot of attention in the last twenty years due to their potential use in photonic devices. In order to have a large second-order NLO response, a compound should not be centrosymmetric, it should have low energy charge-transfer transitions and there should be a large difference between the excited state and ground state dipole moments. Organic compounds with an electron-donor group and an electron-acceptor group connected via a π-conjugated polarizable spacer can reach a good NLO response. Metal complexes have also shown promise due to their accessible low-energy and high-intensity ligand-to-metal, metal-to-ligand, ligand-to-ligand, and intraligand charge transfer (LMCT, MLCT, LLCT, and ILCT) excited states. The energy of these charge transfer states can be readily tuned as a function of the nature and the oxidation state of the metal centre and by the ligands that surround it. Among them, iridium complexes are particularly fascinating, not only for their attractive second-order NLO properties but also for their remarkable two-photon absorption (TPA) properties, a third-order NLO process which is of interest for a number of photonic and optoelectronic applications. The goal of this review is to show the potential of iridium compounds as molecular materials with NLO-activity. First, the principles of second-order nonlinear optics will be briefly introduced, then the review will illustrate the main families of second-order NLO iridium complexes, producing examples of iridium(I) complexes with monodentate nitrogen donor ligands (substituted pyridines and stilbazoles, azaphenanthrene and azachrysene), iridium(III) complexes with terpyridines, bis-cyclometalated phenylpyridine iridium(III) compounds with β-diketonate ligands, tris-cyclometalated phenylpyridine iridium(III) compounds, bis-cyclometalated phenylpyridine iridium(III) complexes with diimines or aryl isocyanides. Through this survey of NLO-phores we show how it is possible to tune the second-order NLO response by a suitable choice of the substituents about the ligands. The emphasis is on second-order NLO properties determined in solution at the molecular level, but examples of nanoorganization of some NLO-active iridium complexes in polymeric matrices to give second-order NLO-active thin films are presented as well. Further, some iridium complexes have shown potential as versatile NLO redox-switching materials and these are described in this review. Finally, a few examples of iridium complexes with TPA properties are given in the last section of the review. The coverage is not comprehensive but provides a suitable introduction to NLO-active iridium complexes and a framework for understanding their potential. [ABSTRACT FROM AUTHOR]

The second-order nonlinear optical (NLO) properties of iridium(III) complexes having two cyclometalated 2-phenylpyridines and curcumin or tetrahydrocurcumin as ancillary ligand have been investigated both in solution and as guest in a polymeric organic matrix. In solution, these complexes are characterized by a significant second-order NLO response, as determined by the Electric Field Induced Second Harmonic (EFISH) technique, like the related complex with acetylacetonate. Whereas the low second-harmonic generation response of a composite film of [Ir(2-phenylpyridine)2(acetylacetonate)] in polymethyl methacrylate was not stable and fell down to zero upon turning off the electric field. A good and stable response was obtained with a film based on the iridium(III) complex bearing two cyclometalated 2-phenylpyridines and curcumin. [ABSTRACT FROM AUTHOR]

Whereas there is an increasing amount of reports on the second-order nonlinear optical (NLO) and luminescence properties of tetradentate [N2O2] Schiff base–zinc complexes, the study of zinc complexes having two bidentate [NO] Schiff-base ligands is relatively unexplored from an NLO point of view. This work puts in evidence that the known chiral bis{2-[(R)-(+)-1-phenylethyliminomethyl]phenolato-N,O}zinc(II) complex is a fascinating multifunctional molecular inorganic–organic hybrid material characterized by interesting second-order NLO and luminescent properties in solution. The emissive properties of the organic 2-(R)-(+)-1-phenylethyliminomethyl]phenol proligand are greatly enhanced upon coordination to the inorganic Zn(II) center. [ABSTRACT FROM AUTHOR]

In this paper, the nonlinear absorption properties of two complexes consisting of Ru(C≡CPh)(C≡C)(dppe)2 (dppe = Ph2PCH2CH2PPh2) as electron donor (D) and 4,7-di(2-thienyl)benzo[c][1,2,5]thiadiazole as electron acceptor (A) units in two different arrangement, i.e., A–D–A and D–A–D, are presented. They were measured in solution by the femtosecond open-aperture Z-scan method. The complexes show moderate two-photon absorption cross-sections σ(2) of several hundred to one thousand GM (here 1 GM = 10−50 cm4 s molecule−1 photon−1). Although they are formed by the same building units, it was found that the two-photon absorption values of the D–A–D arrangement are six times higher than that of the A–D–A one. This difference can be explained by the number of metal cores (one or two ruthenium centers), the geometrical configurations of the complexes (more or less planar), and the resonance enhancement by lowering the intermediate state. [ABSTRACT FROM AUTHOR]

This short review outlines the main results obtained in the field of molecular materials based on zinc coordination compounds for second-order nonlinear optics. It presents an overview of the main classes of second-order nonlinear optical (NLO) active complexes bearing monodentate, bidentate, tridentate, or tetradentate π-delocalized ligands such as substituted stilbazoles, bipyridines, phenanthrolines, terpyridines, and Schiff bases. Macrocyclic ligands such as porphyrins and phthalocyanines are not covered. This paper shows how coordination to the Zn(II) center of π-delocalized nitrogen donor ligands produces a significant enhancement of their quadratic hyperpolarizability. Dipolar complexes are mainly presented, but octupolar zinc complexes are also presented. The coverage is mainly focused on NLO properties that are measured at the molecular level, working in solution, by means of the electric field-induced second harmonic generation (EFISH) or the hyper-Rayleigh scattering (HRS) techniques. [ABSTRACT FROM AUTHOR]

The article presents a study on the use of pentacarbonyl rhenium (Re(CO)5) fragment bonded to a polyhedral oligomeric hydroxysilsesquioxane as model to establish an evidence to the unexpected detection of a surface-anchored Re(CO)5 species. This study indicates that hydroxysilsesquioxane can stabilize Re(CO)5OR species, formerly detected on the silica surface only but never isolated in solution. This article discusses the methods and procedures used in the study.

A series of neutral Ir(2-phenylpyridine) 3 derivatives substituted on the para -position of the pyridyl ligands with a π-conjugated substituent possessing different donor abilities has been prepared. Their two-photon absorption properties have been determined using the Z-scan technique. Such simple iridium(III) neutral complexes, which are easy to synthesize, show good two-photon absorption activity, with relevant TPA cross sections (the best is 750 GM), giving rise to multifunctional chromophores, since they present also high second-order NLO properties.

Three decades ago, dye-sensitized solar cells (DSSCs) emerged as a route for harnessing the sun's energy and converting it into electricity. Since then, an impressive amount of work has been devoted to improving the global photovoltaic efficiency of DSSCs, trying to optimize all components of the device. Up to now, the best efficiencies have usually been reached with ruthenium(II) photosensitizers, even if in the last few years many classes of organic compounds have shown record efficiencies. However, the future of DSSCs is stringently connected to the research and development of cheaper materials; in particular, the replacement of rare metals with abundant ones is an important topic in view of the long-term sustainability of DSSCs intended to replace the consolidated fossil-based technology. In this context, copper is a valid candidate, being both an alternative to ruthenium in the fabrication of photosensitizers and a material able to replace the common triiodide/iodide redox couple. Thus, recently, some research papers have confirmed the great potential of copper(I) coordination complexes as a cheap and convenient alternative to ruthenium dyes. Similarly, the use of copper compounds as electron transfer mediators for DSSCs can be an excellent way to solve the problems related to the more common I 3 - /I - redox couple. The goal of this mini-review is to report on the latest research devoted to the use of versatile copper complexes as photosensitizers and electron shuttles in DSSCs. The coverage, from 2022 up to now, illustrates the most recent studies on dye-sensitized solar cells based on copper complexes as molecular materials.

Substitution of the chlorido ligand of cyclometalated [Pt (5-R-1,3-di(2-pyridyl) benzene)Cl] (R = methyl, mesityl, 2-thienyl, or 4-diphenylamino-phenyl) by 4-phenylthiazole-2-thiolate leads to related thiolato complexes, which were fully characterized. Their photophysical properties were determined in degassed dichloromethane solution. The emission color of the novel complexes can be easily tuned by the nature of the substituents on the terdentate ligand, as is the case for the parent chlorido complexes. Their luminescence Quantum Yield is high, with that of the compounds with the 2-thienyl or 4-diphenylamino-phenyl substituents being much higher than that of the related chloride complexes. The platinum complex with the cyclometalated 5-(2-thienyl)-1,3-di(2-pyridyl) benzene was used as the emitter for the fabrication of a yellow solution-processable OLED.

We disclose a new family of photochromic cyclometalated platinum(II) complexes (PtDTE1 and PtDTE2), where a dithienylethene (DTE) unit is connected at the para-position of the central phenyl ring of (N^C^N) cyclometalated ligand, through two different linkages. Their syntheses are presented along with the X-ray characterizations of both the open and closed isomers of PtDTE1. The investigation of their photophysical properties is made, including absorption, photochromism, emission, and second-order nonlinear properties. We report a quantitative photoisomerization for both PtDTE1 and PtDTE2, irrespective of the nature of the connecting mode between the DTE unit and the platinum(II) moiety. The efficient photochromism allows a significant NLO photomodulation, both in solution and in thin films. In addition, we show that the photoluminescence of the PtDTE1 and PtDTE2 can be controlled by the open/closed isomerization of the DTE unit.

The combination of β-substituted Zn 2+ porphyrin dyes and copper-based electrolytes represents a sustainable route for economic and environmentally friendly dye-sensitized solar cells. Remarkably, a new copper electrolyte, [Cu(2-mesityl-1,10-phenanthroline) 2 ] +/2+ , exceeds the performance reached by Co 2+/3+ and I - /I 3 - reference electrolytes.

A tetracoordinated redox couple, made by [Cu(2-mesityl-4,7-dimethyl-1,10-phenanthroline)2][PF6], 1, and its Cu(II) form [Cu(2-mesityl-4,7-dimethyl-1,10-phenanthroline)2][PF6]2, 2, has been synthesized, and its electrochemical and photochemical features have been investigated and compared with those of a previously published Cu(2+)/Cu(+) redox shuttle, namely, [Cu(2,9-dimethyl-1,10-phenanthroline)2][PF6], 3, and its pentacoordinated oxidized form [Cu(2,9-dimethyl-1,10-phenanthroline)2Cl][PF6], 4. The detrimental effect of the fifth Cl(-) ancillary ligand on the charge transfer kinetics of the redox shuttles has been exhaustively demonstrated. Appropriately balanced Cu-based electrolytes have been then formulated and tested in dye solar cells in combination with a π-extended benzothiadiazole dye. The bis-phenanthroline Cu-complexes, 1 and 2, have been found to provide an overall 4.4% solar energy conversion efficiency, which is more than twice that of the literature benchmark couple, 3 and 4, employing a Cl-coordinated oxidized species and even comparable with the performances of a I(-)/I3(-) electrolyte of analogous concentration. A fast counter-electrode reaction, due to the excellent electrochemical reversibility of 2, and a high electron collection efficiency, allowed through the efficient dye regeneration kinetics exerted by 1, represents two major characteristics of these copper-based electron mediators and may constitute a pivotal step toward the development of a next generation of copper-based efficient iodine-free redox shuttles.

In the context of the development of new electron mediators for dye-sensitized solar cells that could efficiently substitute the more common I3(-)/I(-) redox couple, we have prepared a series of Cu(I)- phenanthroline complexes through an easy synthetic route. The novel [Cu(2-mesityl-4,7-dimethyl-1,10-phenanthroline)2]PF6 (3) is of particular interest because the presence of the bulky mesityl groups protects as a kiss lock the Cu center, leading to superior dye regeneration kinetics with respect to simpler phenanthroline-based Cu(I) complexes and to a lower dark current with respect the I3(-)/I(-). The exploitation of a dual-component electrolyte constituted by (3) and a Fe(II) comediator, in combination with the [Ru(4,4'-dicarboxy-2,2'-bipyridine)2(4,4'-dinonyl-2,2'-bipyridine)](PF6)2 sensitizer, allowed us to increase the performance of the cell, reaching Jsc values of 4.0 mA cm(-2), comparable to that recorded with I3(-)/I(-) (3.8 mA cm(-2)).

The second order nonlinear optical (NLO) properties of various simple tris-cyclometallated Ir(III) complexes bearing 2-phenylpyridine ligands have been investigated by means of the EFISH technique, evidencing how appropriate substitution of the cyclometallated ligands may allow the tuning of the second-order NLO response of this unusual family of 3D chromophores. To evaluate the dipole moments and to gain insight into the electronic structure and optical properties of the investigated complexes we also performed Density Functional Theory (DFT) calculations.

The first examples of thiocyanate-free thiophene-substituted Ru(II) cyclometalated complexes, based on thiophene-derived 2-(2,4-difluorophenyl)pyridine ligands, are presented and investigated as photosensitizers in DSCs. Upon thiophene substitution the complexes presented enhanced optical properties compared to the reference dye with no thiophene substitution. DSCs based on the dithienyl-derived dye showed power conversion efficiencies up to 5.7%, more than twice that containing the complex without the thiophene substitution.

Ionic transition metal complexes (iTMCs) have already been demonstrated to be a promising type of material to fabricate low-cost light sources, which are much more competitive in terms of realization costs with respect to standard organic light emitting diodes. The device performance, optical and morphological properties of thin films of two different complexes [Ir(phenylpyridine)(2)(5-Me-1,10-phen)][PF(6)] and [Ir(phenylquinoline)(2)(5-Me-1,10-phen)][PF(6)] have been measured and compared. The use of an ionic liquid as part of the processing procedure shows advantages in terms of low operation voltage, which is as low as 3.5 Volts. However, it leads to drawbacks in terms of device lifetime, limited to t(1/2) = 2 min, and maximum achievable brightness (1425 cd m(-2) vs. 3040 cd m(-2) without ionic liquid, for the complex [Ir(phenylpyridine)(2)(5-Me-1,10-phen)][PF(6)]).

The dipolar and octupolar contributions of the second order nonlinear optical properties of [(4'-(C(6)H(4)-p-D)-2,2':6',2''-terpyridine)-Ru-(4'-(C(6)H(4)-p-A)-2,2':6',2''-terpyridine)]Y(2) heteroleptic complexes (D and A are donor and acceptor groups, respectively), and related free terpyridines and homoleptic complexes, have been obtained by means of a comprehensive combination of Electric Field Induced Second Harmonic generation, Third Harmonic Generation, and Harmonic Light Scattering measurements. These results evidence how a metal can act as a bridge between two π-delocalized terpyridine moieties bearing a D and an A group, respectively, leading to a large quadratic hyperpolarizability hugely dominated by the octupolar contribution.

[PtL(6)X] {X = Cl or NCS and L(6) = 5-mesityl-1,3-di(2-pyridyl)-benzene} display similar luminescence in solution but, in the solid state, the packing of the molecules is different, with short PtPt interactions for X = NCS, leading to a red-shifted emission band. The effect has been used to generate OLEDs that emit squarely in the NIR region (855 nm)., (This journal is © The Royal Society of Chemistry 2012)

We present relevant results dealing with the transparency/optical nonlinearity trade-off in high-frequency electro-optic applications. The very simple, stable and high optical gap chromophore, the zwitterion 1-methyl-4-(tetrazol-5-ate)pyridinium, represents the best transparency/optical nonlinearity trade-off so far described in the literature. We rationalize this remarkable performance in the framework of the Bond Length Alternation theory by means of a multidisciplinary approach including: single crystal X-ray structure, Electric Field Induced Second-Harmonic Generation, solvatochromism, electrochemistry and thermal analyses.

Cyclometalated cationic Ir(III) complexes with substituted 1,10-phenanthrolines (1,10-phen), such as [Ir(ppy)(2)(5-R-1,10-phen)]Y (ppy=cyclometalated 2-phenylpyridine; R=NO(2), H, Me, NMe(2); Y(-)=PF(6) (-), C(12)H(25)SO(3) (-), I(-)) and [Ir(ppy)(2)(4-R,7-R-1,10-phen)]Y (R=Me, Ph) are characterized by a significant second-order optical non linearity (measured by the electrical field induced second harmonic generation (EFISH) technique). This nonlinearity is controlled by MLCT processes from the cyclometalated Ir(III), acting as a donor push system, to pi* orbitals of the phenanthroline, acting as an acceptor pull system. Substitution of cyclometalated 2-phenylpyridine by the more pi delocalized 2-phenylquinoline (pq) or benzo[h]quinoline (bzq) or by the sulfur-containing 4,5-diphenyl-2-methyl-thiazole (dpmf) does not significantly affect the mubeta absolute value, which instead is affected by the nature of the R substituents on the phenanthroline, the higher value being associated with the electron-withdrawing NO(2) group. By using a combined experimental (the EFISH technique and (1)H and (19)F PGSE NMR spectroscopy) and theoretical (DFT, time-dependent-DFT (TDDFT), sum over states (SOS) approach) investigation, evidence is obtained that ion pairing, which is controlled by the nature of the counterion and by the concentration, may significantly affect the mubeta values of these cationic NLO chromophores. In CH(2)Cl(2), concentration-dependent high absolute values of mubeta are obtained for [Ir(ppy)(2)(5-NO(2)-1,10-phen)]Y if Y is a weakly interacting anion, such as PF(6) (-), whereas with a counterion, such as C(12)H(25)SO(3) (-) or I(-), which form tight ion-pairs, the absolute value of mubeta is lower and quite independent of the concentration. This mubeta trend is partially due to the perturbation of the counterion on the LUMO pi* levels of the phenanthroline. The correlation between the mubeta value and dilution shows that the effect of concentration is a factor that must be taken into careful consideration.

[Ir(ppy)(2)(RCOCR'COR)] and [Pt(ppy)(RCOCHCOR)] (ppy = cyclometallated 2-phenylpyridine; R = Me, Ph; R' = H, 2,4-dinitrophenyl) complexes show an unexpected large second order non linear optical response, as evidenced by the EFISH technique, which can be attributed by an SOS-TDDFT investigation mainly to intraligand charge transfer transitions involving the cyclometallated ligands.

The structural, emissive, and nonlinear optical properties of new CuI adducts with para-substituted trans-stilbazolic and pyridinic ligands are reported. Single-crystal X-ray diffraction results indicate that the para-substituent on the organic ligand greatly influences the structural motif by its steric (tert-butyl), electronic/steric (dimethylamino), or bridging-donor (cyano) properties so that two absolutely new structural motifs, polymeric and oligomeric, are found when trans-stilbazole and pyridine carry a dimethylamino group in the para-position. In addition, a surprising photoemission behavior is observed, being the solid-state emission of [CuI(trans-4-stilbazole)]n, [CuI(trans-4'-(dimethylamino)-4-stilbazole)]n, and [CuI(4'-tert-butyl-4-stilbazole)]n totally quenched. In the case of the noncentrosymmetric CuI adduct of trans-4'-(dimethylamino)stilbazole a discrete second harmonic generation (SHG) occurs.

[Os(3)(CO)(12)], [H(4)Os(4)(CO)(12)], [H(2)Os(4)(CO)(12)](2)(-), [Os(5)C(CO)(14)](2)(-), and [Os(10)C(CO)(24)](2)(-) have been synthesized selectively and in high yields by reductive carbonylation or hydrogenation of OsCl(3) or alpha-[Os(CO)(3)Cl(2)](2) supported on silica in the presence of alkali carbonates. The selectivity of the reaction is controlled by the choice of (i) the nature and quantity of the alkali carbonate (Na(2)CO(3) or K(2)CO(3)) added to silica, (ii) temperature, (iii) reaction time, and (iv) the gas-phase composition (CO, CO + H(2), or H(2)). These surface-mediated syntheses are often more selective and more efficient and usually require less drastic conditions than the best known syntheses in solution, confirming the potential use of the silica surface as a new reaction medium to prepare both neutral and anionic metal carbonyl clusters.