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International audience; Three novel luminescent iridium(III) dyes functionalized with a tryptophan amino acid and bearing two cyclometalated 2-phenylpyridines, 2-(2,4-difluorophenyl)pyridines or 2-phenylquinolines have been prepared and well characterized. They emit at 522-561 nm with a luminescence quantum yield in the range 0.33-0.98. All the dyes are able to stain neuronal cells in rat cerebellum tissue, as evidenced by fluorescence microscopy, showing affinity for granule neurons. The complexes bearing cyclometalated 2-(2,4-difluorophenyl)pyridines or 2-phenylquinolines also have a good affinity for brain white matter. The dye with two cyclometalated 2-phenylquinolines is characterized by the best luminescence quantum yield (0.98). Besides, giving the greatest image contrast, the dye with two cyclometalated 2-phenylquinolines shows the strongest affinity for a distinct subtype of neurons found in cerebellum tissue, the purkinje neurons (as evidenced with fluorescence microscopy).

The preparation and characterization of a new platinum(ii) complex bearing a N^C^N-cyclometalating ligand and a thiolate coligand, namely 5-mesityl-1,3-di-(2-pyridyl)benzene and 1-phenyl-1H-tetrazole-5-thiolate, is reported. Its structure is determined by X-ray diffraction studies on a single crystal. This new complex exhibits green and red phosphorescence in dichloromethane solution (?lum = 0.90) and in the solid state (?lum = 0.62), respectively. In both cases the quantum yield is impressive showing for the first time that N^C^N platinum(ii) complexes with a suitable thiolate coligand can reach outstanding luminescence properties. The excellent solubility of this complex allows fabrication of green processable solution-OLEDs with maximum EQE similar to that obtained with more expensive vacuum techniques and, depending on its concentration, one can tune the color of the OLED. The molecular geometry, ground state, electronic structure, and excited electronic states of the complex, both as a monomer and dimer aggregate in solution, are calculated by density functional theory (DFT) and time-dependent DFT approaches, giving insight into the electronic origin of the absorption spectra. Remarkably, the dimer is less sensitive to oxygen quenching than the monomer because the two 1-phenyl-1H-tetrazole fragments protect the platinum(ii) centers, as suggested by a combination of luminescence studies and theoretical calculations.

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. 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.

International audience; 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 p-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 intralig and (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 compound shaving 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 redoxswitchable NLO properties are also given. Although the accent is on the quadratic hyperpolarizability measured in solution, it is also shown how some NLO-activeplatinumcomplexes canbenano-organized to afford thinfilmswithnonlinear optical properties. Thereport is notcomprehensive, butit allows to get into the field of NLO-active platinum compounds and to understand their potential.

Curcumin has chemopreventive properties against a variety of tumours, but it has poor bioavailability. Two new bis‐cyclometallated iridium(III) complexes have been prepared, featuring the natural product curcumin (CUR) or its reduced form, tetrahydrocurcumin (THC), as bidentate, anionic O^O‐binding ligands. The iridium THC complex is highly luminescent in deoxygenated solution and efficiently generates singlet oxygen under aerated conditions, whereas in the curcumin analogue, other non‐radiative decay pathways are competitive. The complexes are rapidly taken up into a variety of human tumour cell lines from solutions of micromolar concentration. They have negligible cytotoxicity in the absence of irradiation. When briefly irradiated by visible light, Ir‐THC becomes highly phototoxic, inducing rapid apoptosis within 2 h. The results show the high potential of such complexes as sensitizers in photodynamic therapy (PDT).

The synthesis and characterization of two simple Ruthenium(II) complexes of the type [Ru(X^N)2(4,4′-dicarboxybipyridine)]+ (with X[dbnd]C, X^N[dbnd]benzoquinolinate, 1; with X[dbnd]N, X^N[dbnd]2-pyridyl tetrazolate, 2) and the exploitation of a new carbon doped anatase TiO2 paste in dye-sensitized solar cells (DSSCs) photoanode are described. In particular, glucose (C6H12O6) is used as a new chemical eco-friendly C-dopant during the doping process of anatase TiO2 nanoparticles. The proper combination of Ru(II) sensitizers and C-doped titania can afford efficient DSSC photoanodes. All the relevant photovoltaic parameters have been determined.

International audience; Five new platinum(ii) complexes bearing a cyclometallated 5-π-delocalized donor-1,3-di(2-pyridyl)benzene were prepared and fully characterized. Their second-order nonlinear optical (NLO) properties were determined by the Electric-Field Induced Second Harmonic generation (EFISH) technique, working in DMF solution with an incident wavelength of 1907 nm, whereas the dipole moments were determined by Density Functional Theory (DFT) calculations. Remarkably, the platinum(ii) complex with a cyclometallated 5-guaiazulene-CH[double bond, length as m-dash]CH-1,3-di(2-pyridyl)benzene appears as a very good candidate for application in photonics, being characterized by the largest second-order NLO response. Besides, it appeared that the nature of substituents on thiophene, chosen as π-delocalized moiety in position 5 of the 1,3-di(2-pyridyl)benzene, strongly affects the NLO properties.

Three new perylenetetracarboxy-3,4:9,10-diimides, bearing 2,6-diisopropylphenyl groups at the imide positions and 4-(R-ethynyl)phenoxy moieties (R = 4,7-di(2-thienyl)benzo[c][1,2,5]thiadiazole (P2), pyrene (P3) or pyrene-CH2OCH2 (P4)) at the four bay positions, were prepared, along with the known related derivative (R = phenyl (P1)), and well characterized. They have large two-photon absorption (TPA) cross-sections (σ2), as determined by the Z-scan technique, the highest values being reached with P2 which bears a planar π-delocalized donor moiety. P3 is characterized by higher σ2 values than both P1, as expected for the higher π-conjugation of the donor pyrene moiety with respect to phenyl, and P4, due to the presence of the flexible and non-conjugated CH2OCH2 bridge between the pyrene and the ethynyl fragment in the latter compound. The molecular geometry of P1–P4 has been optimized by DFT modeling, showing that in P2 and P3 the bay substituents are stacked due to the π–π interactions of both pyrene and thiophene groups. The LUMO of P1–P4 lies at the same energy and is essentially delocalized on the perylene core whereas the HOMO and HOMO−1 of both P2 and P3 are degenerate and do not show contribution from the perylene core contrarily to that of P1 and P4. The HOMO–LUMO gap is therefore essentially influenced by the HOMO which reflects the electronic charge delocalization on the bay substituents, the lower gaps being observed for P2 and P3, which are characterized by the best TPA properties.

Two new heteroleptic copper(i) sensitizers bearing 6,6'-dimethyl-2,2'-bipyridine-4,4'-dibenzoic acid, to anchor the dye on the titania surface, and a π-delocalized 2-(R-phenyl)-1H-phenanthro[9,10-d]imidazole (R = NPh2 or O-hexyl) ancillary ligand were prepared and well characterized. Their performance as dyes in DSSCs is quite similar to that of the related complex bearing 2,9-dimesityl-1,10-phenanthroline as an ancillary ligand, when using the common I-/I3- redox couple or homoleptic copper complexes as electron shuttles. The experimental results along with theoretical calculations confirm the great potential of full-copper DSSCs.

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.

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.

New Y-shaped ferrocene conjugated imidazole chromophores were prepared and fully characterized. The Y-shaped structure was confirmed by the single crystal X-ray diffraction technique. The chromophores show interesting second-order nonlinear optical (NLO) properties in solution, as determined by the Electric-Field Induced Second Harmonic generation (EFISH) technique. Remarkably, the trifluoro substituted compound 3 is characterized by a high mu beta(EFISH) value and has good potential as a molecular building block for composite films with Second Harmonic Generation (SHG) properties. For all compounds, the dipole moments and frontier orbital energies were calculated by the Density Functional Theoretical method.

International audience; 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 p-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 beta-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.

The effect on the second-order nonlinear optical properties of the nature of the pi-delocalized moiety in the position 5 of a 1,3-di(2-pyridyl)benzene cyclometallated to a platinum(II) center was investigated. The influence of the substitution of a double bond with a triple bond as bridge between a triphenylamino group and the cyclometallated phenyl ring was studied and turned out to be negligible. Remarkably, the novel easily-prepared platinum(II) complex with a cyclometallated 5-styryl-1,3-di(2-pyridyl)benzene is characterized by a good second-order NLO response, as determined in solution by the EFISH technique; it is a good candidate for application in photonics. (C) 2017 Elsevier Ltd. All rights reserved.

The use of a copper(I) dye, bearing a 2,9-dimesityl-1,10-phenanthroline and a 6,6′-dimethyl-2,2′-bipyridine-4,4′-dibenzoic acid, was investigated in DSSCs with various electrolyte solutions based on two different redox mediators, namely the common I−/I3− couple and an interesting copper electron shuttle. The experimental results provide evidence of the importance of the redox mediator concentration and the crucial role of additives such as 4-tert-butylpyridine and lithium bis(trifluoromethanesulfonyl)imide in the performance of sustainable “full-copper” DSSCs, consolidating the way to DSSCs with Earth-abundant components.

In this paper, the nonlinear absorption properties of two complexes consisting of Ru(C&equiv, CPh)(C&equiv, 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&ndash, D&ndash, A and D&ndash, A&ndash, 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 &sigma, (2) of several hundred to one thousand GM (here 1 GM = 10&minus, 50 cm4 s molecule&minus, 1 photon&minus, 1). Although they are formed by the same building units, it was found that the two-photon absorption values of the D&ndash, D arrangement are six times higher than that of the A&ndash, 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.

Curcumin has chemopreventative properties against a variety of tumours, but has poor bioavailability. Here, two new bis-cyclometallated iridium(III) complexes have been prepared, featuring the natural product curcumin (CUR) or its reduced form, tetrahydrocurcumin (THC), as bidentate, anionic O O-binding ligands. The iridium THC complex is highly luminescent in deoxygenated solution and efficiently generates singlet oxygen under aerated conditions, whereas in the CUR analogue, other non-radiative decay pathways are competitive. The complexes are rapidly taken up by a variety of human tumour cell lines from solutions of micromolar concentration. They show negligible cytotoxicity in the absence of irradiation. When briefly irradiated with visible light, Ir-THC becomes highly phototoxic, inducing rapid apoptosis within 2 h. The results show the high potential of such complexes as sensitizers in photodynamic therapy (PDT).

Thirty years ago, dye-sensitized solar cells (DSSCs) emerged as a method for harnessing the sun’s energy and converting it into electricity. Since then, a lot of work has been dedicated to improving their global photovoltaic efficiency and their eco-sustainability. Recently, various articles showed the great potential of copper complexes as a convenient and cheap alternative to the traditional ruthenium dyes. In addition, copper complexes demonstrate that they can act as redox mediators for DSSCs, thus being an answer to the problems related to the I3−/I− redox couple. The aim of this review is to report on the most recent impact made by copper complexes as alternative redox mediators. The coverage, mainly from 2016 up to now, is not exhaustive, but allows us to understand the great role played by copper complexes in the design of eco-sustainable DSSCs.

In the early 1990s, dye-sensitized solar cells (DSSCs), fabricated by O'Regan and Graetzel, emerged as a realistic solution for harnessing the energy of the sun and converting it into electricity. Since then, an impressive amount of work has been carried out in order to improve the global photovoltaic efficiency of DSSCs, trying to optimize every components of the device in terms of material, structure and activity. Up to now, the best efficiencies have been reached with zinc–porphyrin and Ru(II) photosensitizers, but recently an exponential growth of articles showed the great potential of copper(I) coordination compounds as a convenient and cheap alternative. Similarly, it appeared that the use of copper complexes as electron transfer mediators for DSSCs can be an excellent way to solve the problems related to the more common I3–/I– redox couple. The goal of this review is to report on the promising use of versatile copper complexes as photosensitizers and electron shuttles in DSSCs which had a real boom in the last few years. The coverage, mainly from 2010 up to now, is not exhaustive, but allows the non-specialist reader to get into this specific field and to understand its potentiality. An important message that the review will convey is the mandatory role of comparing results on novel photosensitizers and/or on alternative redox mediators with well-established literature reference systems such as N719 dye and I3–/I–-based electrolyte, respectively. In fact, reporting the performance of new compounds with respect to proper standard materials is the unique secure method to correctly and, firstly, constructively compare data from different studies.

The synthesis and second-order nonlinear optical (NLO) properties of seven novel fullerene-C60 derivatives are reported. In these donor–bridge–acceptor systems, the fullerene unit (acceptor) is connected through a cyclopropane ring to an ethynyl thienyl fragment (bridge) which binds a trimethylsilyl or platinum alkynyl fragment (donor). All derivatives are NLO-active, as determined by the electric field induced second harmonic generation technique, but the fullerene platinum alkynyl complexes are characterized by a particularly large second-order NLO response. Substitution of the thienyl fragment by a terthiophene leads to an increase of the NLO performance by using trimethylsilyl as a donor group, whereas no effect is observed in the case of platinum derivatives. Remarkably, fullerene platinum alkynyl complexes can be dispersed in poly(methyl methacrylate) or polystyrene, affording NLO-active polymer films.

International audience; 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 photo-isomerization 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 photo-modulation, 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.

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.

Contamination of surface water, groundwater and soil by halogenated organic compounds (HOCs) is a major problem of our society. HOCs have been used in a wide variety of applications and their presence as water contaminant is now a serious issue because of their toxicity, persistence and potential accumulation in plants and animal tissues. Transformation of HOCs by zero-valent iron represents a promising technology for environmental remediation. This mini-review outlines how iron particles are able to degrade toxic HOCs in water. It shows how the addition of one or two metals, such as palladium, copper, silver and nickel, to form bi- and tri-metallic particles can lead to a more efficient decontamination. Other ways to enhance the degradation of HOCs are the use of additives and ultrasounds. Another interesting approach is to anchor the metallic particles on various supports. Examples of the various approaches are given.

International audience; 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.

The synthesis and characterization of three 5-p-delocalized-donor-1,3-di(2-pyridyl) benzenes is reported along with that of their related cyclometallated platinum(II) complexes and N, N-dimethylated iodide salts. The second-order nonlinear optical (NLO) properties of all the compounds have been determined by the Electric Field Induced Second Harmonic generation technique, showing how the mu beta(EFISH) absolute value of 1,3-di(2-pyridyl) benzenes can be tuned by the nature of the substituent on position 5 of the central benzene ring, and greatly increased by cyclometallation to Pt or by N-methylation.

The combination of ?-substituted Zn2+ 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 Co2+/3+ and I-/I3- reference electrolytes.

A novel copper(I) complex bearing two 6,6′-dimethyl-2,2′-bipyridine-4,4′-dibenzoic acid ligands was prepared along with related deprotonated derivatives with Na+ or NBu4+ as counterion. Their performance as photosensitizer in dye sensitized solar cells was studied as a function of the anchoring group and the electrolyte composition, comparing it with that of the known copper(I) complex bearing two 6,6′-dimethyl-2,2′-bipyridine-4,4′-dicarboxylic acid ligands and the ruthenium benchmark N719. Interestingly, the novel protonated complex is characterized by the best overall power conversion efficiency (3.0%) reported up to now for a copper(I) complex.

In the present work, we report a convenient synthesis with a microwave reactor of [Ru(quo)(dcbpy)2]+Cl (quo = 8-hydroxyquinolinate, dcbpy = 2,2′-bipyridinyl-4,4′-dicarboxyl acid) and of the parental complex [Ru(Me2-quo)(dcbpy)2] +Cl (Me2-quo = 5,7-dimethyl-8-hydroxyquinolinate) along with their electrochemical and photovoltaic characterization. © 2013 Elsevier B.V. All rights reserved.

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.

International audience; We disclose two unprecedented complexes built with a central dithienylethene photochrome connecting two cyclometalated Pt(ii) moieties either on the reactive carbon atoms or on the lateral non-reactive carbon atoms of the photochrome. The two systems show vastly different properties that are rationalised thanks to quantum-chemical calculations. © The 2016 The Royal Society of Chemistry.

International audience; A series of cationic Ir(III) substituted bipyridyl ()(N(∧)N (N(∧)N-bpy) complexes incorporating electron-donor and -acceptor substituents, [Ir(C(∧)N-ppy-R')(2)(N(∧)N-bpy-CH═CH-C(6)H(4)-R)][X] (X(-) = PF(6)(-) or C(12)H(25)SO(3)(-)), 2 (a, R = NEt(2) and R' = Me; b, R = O-Oct and R' = Me; c, R = NO(2) and R' = C(6)H(13); C(∧)N-ppy = cyclometalated 2-phenylpyridine, [Ir(C(∧)N-ppy-Me)(2)(N(∧)N-bpy-CH═CH-thienyl-Me)][PF(6)], 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 (PF(6)(-), C(12)H(25)SO(3)(-)) 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 N(∧)N-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.

A new dinuclear Ru(II) complex where two Ru atoms are separated by a bridge consisting of a 2,1,3-benzothiadiazole acceptor moiety flanked on either side by 2,5-thienyldonor units was synthesized. This rather simple complex appears to behave as a photoactive donor when blended with a fullerene as acceptor, thus being a first step toward novel bulk heterojunction solar cells, based on Ru donor systems

The second-order nonlinear optical (NLO) properties of [Ln(hfac)(3)(diglyme)] (hfac = hexafluoroacetylacetonate; 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 f 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, beta(EFISH), 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 beta(EFISH) value of the Lu complex being only 1.2 times that of the Gd complex. The increase of , which is dominated by an octupolar contribution, is much lower along the Ln series. Remarkably, the good values of these simple systems, well known for their luminescence properties, are reached at no cost of transparency.

A series of 4-X-1-methylpyridinium cationic nonlinear optical (NLO) chromophores (X = (E)-CH=CHC(6)H(5); (E)-CH=CHC(6)H(4)-4'-C(CH(3))(3); (E)-CH=CHC(6)H(4)-4'-N(CH(3))(2); (E)-CH=CHC(6)H(4)-4'-N(C(4)H(9))(2); (E,E)-(CH=CH)(2)C(6)H(4)-4'-N(CH(3))(2)) with various organic (CF(3)SO(3)(-), p-CH(3)C(6)H(4)SO(3)(-)), inorganic (I(-), ClO(4)(-), SCN(-), [Hg(2)I(6)](2-)) and organometallic (cis-[Ir(CO)(2)I(2)](-)) counter anions are studied with the aim of investigating the role of ion pairing and of ionic dissociation or aggregation of ion pairs in controlling their second-order NLO response in anhydrous chloroform solution. The combined use of electronic absorption spectra, conductimetric measurements and pulsed field gradient spin echo (PGSE) NMR experiments show that the second-order NLO response, investigated by the electric-field-induced second harmonic generation (EFISH) technique, of the salts of the cationic NLO chromophores strongly depends upon the nature of the counter anion and concentration. The ion pairs are the major species at concentration around 10(-3) M, and their dipole moments were determined. Generally, below 5x10(-4) M, ion pairs start to dissociate into ions with parallel increase of the second-order NLO response, due to the increased concentration of purely cationic NLO chromophores with improved NLO response. At concentration higher than 10(-3) M, some multipolar aggregates, probably of H type, are formed, with parallel slight decrease of the second-order NLO response. Ion pairing is dependent upon the nature of the counter anion and on the electronic structure of the cationic NLO chromophore. It is very strong for the thiocyanate anion in particular and, albeit to a lesser extent, for the sulfonated anions. The latter show increased tendency to self-aggregate.

The anionic rhodium carbonyl clusters [Rh 7 (CO) 16 ] 3− and [Rh 14 (CO) 25 ] 4− can be easily prepared by a new simple and high yield one-pot synthesis starting from RhCl 3 · n H 2 O dissolved in ethylene glycol and involving two steps: (i) treatment of RhCl 3 · n H 2 O under 1 atm of CO at 50 °C to give [Rh(CO) 2 Cl 2 ] − ; (ii) addition of a base (CH 3 CO 2 Na or Na 2 CO 3 ) followed by reductive carbonylation under 1 atm of CO at an adequate temperature (50 °C for [Rh 7 (CO) 16 ] 3− ; 150 °C for [Rh 14 (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 1 atm 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 [Rh 14 (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 [Rh 7 (CO) 14 ] − and [Rh 15 (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.

A correlated photoluminescence (PL) and electroluminescence (EL) investigation of light-emitting electrochemical cells based on [Ir(4,5-diphenyl-2-methylthiazolo)2(5-methyl-1,10-phenanthroline)]+ [PF6]− reveals the excimer nature of the EL emission. Excimers are formed when the device is biased and the EL emission energy is a fingerprint of the excimer intermolecular interactions induced by the local electric field at the applied voltage. Imaging measurements provide evidence that the molecular rearrangement into aggregates favors the formation of excimer states, which are irreversibly formed once the device is biased and are the preferential emitting states even in devices left unbiased for a long period of time. PL lifetime measurements in working devices provide unambiguous evidence of the excimer character of EL. These results show that excimers play a role in the mechanism of operation and performance degradation of organic light-emitting electrochemical cells (OLEC) based on ionic transition metal c...

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 730-930 nm 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. © 2009 Elsevier B.V. All rights reserved.