Search

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 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.

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.

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 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

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...

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.

The acidochromic behaviour of trans-5-(p-(N, N-diphenylamino)styryl)-1,3-di(2-pyridyl)benzene (1) and 5-(p-(N, N-diphenylamino) phenylethynyl)-1,3-di(2-pyridyl) benzene (2) was investigated, both in solution and doped into films, studying their linear and nonlinear optical properties. Remarkably, the efficient luminescence of 1 drops drastically upon protonation and is restored upon deprotonation - both in solution and in the solid state - leading to an excellent on/off emissive acido-triggered reversible switch. In parallel, protonation leads to a large enhancement of the second-order NLO response, as determined by the EFISH technique, which is reversible upon deprotonation. The related methylated salts of 1 and 2 are similarly characterized by a high NLO response.

Coordination of 4'-(C6H4-p-X)-2,2':6',2''-terpyridines [X = NO2, NBu2, (E)-CH=CH-C6H4-p-NBu2, (E,E)-(CH=CH)2-C6H4-p-NMe2] to Zn(II), Ru(III), and Ir(III) metal centers induces a significant enhancement of the absolute value of the second-order nonlinear optical (NLO) response of the terpyridine, measured by means of both electric field induced second harmonic generation and solvatochromic methods. By varying the nature of the metal center, the enhanced second-order NLO response shifts from positive to negative. Such a shift is controlled by electronic charge-transfer transitions, such as metal-to-ligand or ligand-to-metal transitions, in addition to the intraligand charge transfer. The enhancement generated by coordination is also controlled by the chelation effect and by fine-tuning of the ancillary ligands.

The new ligands (E)-4-[2-(4-(N-methyl-N-hexadecylaminophenyl)ethenyl]pyridine (L1) and 4′-(C6H4-p-N(Me)(hexadecyl))-2,2′:6′,2″-terpyridine (L2) were prepared along with their complexes [cis-Ir(CO)2ClL1], [fac-Os(CO)3Cl2L1], [ZnCl2L2] and [IrCl3L2]. Whereas these complexes show a large second-order nonlinear optical (NLO) response at the molecular level, similar to that of related organic alkylated salts as evidenced by the Electric Field Induced Second-Harmonic (EFISH) generation technique, their Langmuir–Blodgett (LB) film susceptibility is lower than that of the salts.

The synthesis of the new complex [Ru(Tetrazpy)(dcbpy)2]Cl is reported, along with its spectroscopical, electrochemical, and theoretical characterization. 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.

We report the synthesis, electronic properties, and second-order nonlinear optical (NLO) response of asymmetric heteronuclear push−pull bimetallic complexes with pyrazine (pyz) and trans-1,2-bis(4-...

Novel photochromic dithienylethene-based platinum(II) complexes.((CNN)-N-boolean AND-N-boolean AND)Pt(C C-DTE-C6H4-D) (((CNN)-N-boolean AND-N-boolean AND) = 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 pi-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.

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)).

For fluorescent compounds, the combined use of absorption and emission solvatochromic data allows to estimate indirectly the cavity radius of the molecule in solution, a very critical parameter in the application of the solvatochromic method for the determination of the quadratic hyperpolarizability β of dipolar molecules. For two test compounds, trans-4-[4-(dimethylamino)styryl]pyridine (DASP) and 5-dimethylamino-1,10-phenanthroline (DAPHEN), the β values so obtained are compared with those obtained by the EFISH (Electric Field Induced Second-Harmonic generation) technique. For DAPHEN, the versatility of the method described in this work in the presence of more than one electronic transition contributing to the non-linear optical response is demonstrated.

Coordination of para-substituted pyridines 4-X-C5H4N (where X = NMe2, CMe3, H, COMe, CN) to metal carbonyl moieties such as “cis-M(CO)2Cl” (M = Rh(I), Ir(I)) and “fac-Os(CO)3Cl2” produces an enhancement up to about 2 orders of magnitude of the quadratic hyperpolarizability βλ of the free pyridine. This effect is due either to a red shift of the intraligand charge-transfer (ILCT) transition upon coordination (when X is a strong electron donor) or to a significant effect on the metal-to-ligand charge-transfer (MLCT) transitions (when X is a strong electron acceptor). In this latter case the quadratic hyperpolarizability may assume a negative sign, due to the negative value of Δμeg upon excitation. Therefore we confirmed that as already shown by metal carbonyl moieties such as “M(CO)5” (M = Cr, W), a soft metal center displays, from the point of view of the perturbation of the quadratic hyperpolarizability of pyridines, an ambivalent acceptor or donor role. The quadratic hyperpolarizability of complexes of m...

International audience; 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.

The second-order nonlinear optical (NLO) properties of various Pt(II) acetylcetonate complexes bearing a substituted cyclometalated 4-styryl-2-phenylpyridine (ppy-4-styryl-R, with R = NEt2, OMe, H, NO2) were investigated in DMF solution on working with an incident wavelength of 1907 nm by the EFISH technique, whereas the dipole moments were determined by density functional theory (DFT) calculations. In addition, a Pt(II) complex with the ppy-4-styryl-NEt2 ligand, which was the most NLO efficient chromophore due to a particularly high dipole moment, was dispersed in a polymethylmethacrylate matrix and then oriented by poling to give a composite film characterized by a good and quite stable second harmonic generation (SHG) signal. © 2013 American Chemical Society.

International audience; 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.

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 [PtLX] 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.

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.

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.

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.

A new thiocyanate-free cyclometallated 2-phenylpyridine Ru(II) complex, [Ru(dFppyCF 3)(dcbpy) 2] +PF 6- (dFppyCF 3 = 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] +PF 6-. Substitution of the pyridine ring by the CF 3 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. © 2012 Elsevier B.V. All rights reserved.

The Pt(II) complex N boolean AND C(2 boolean AND)N-1,3-di(2-pyridyl) benzene platinum chloride (PtL(1)Cl) is known to display efficient triplet luminescence in the green region of the spectrum, and to form an unusually emissive excimer that emits around 690 nm. In this contribution, the introduction of trifluoromethyl groups into either the 4- or 5-position of the pyridyl rings of the ligand is shown to lead to a red-shift in the excimer band, moving it into the near infra-red (NIR) region. The new ligands, synthesised by either Suzuki or Stille cross-coupling methods, are 1,3-bis(4-(trifluoromethyl) pyridin-2-yl)benzene HL(27), 1,3-bis(4-(trifluoromethyl) pyridin-2-yl)-4,6-difluorobenzene HL(28), and 1,3-bis(5-(trifluoromethyl) pyridin-2-yl)-4,6- difluorobenzene HL(29), from which the corresponding Pt(II) complexes PtL(n)Cl have been prepared. The monomer and excimer emission energies in solution are compared with those of PtL(1)Cl and PtL(22)Cl {HL(22) = 1,3-di(2-pyridyl)-4,6-difluorobenzene}. The order for the monomer can be rationalised in terms of the stabilising effects of the F atoms and the CF(3) groups on the HOMO and LUMO respectively. The order of excimer emission proves to be subtly different, but the most red-shifted complex in both cases is PtL(27)Cl. The electroluminescence of neat films of the complexes as emitting layers in OLEDs displays uniquely excimer-like emission, extending well into the technologically important NIR region.

Two families of thiophene-based 2-arylpyridines, in which aryl is phenyl and 2,4-difluorophenyl, have been developed. The pyridine ring of the new compounds is substituted at the 4-position with π-conjugated electron-rich and electron-poor thiophene-based fragments to tune the optical and energetic properties. The high-yielding synthetic access, which consists of two sequential Suzuki coupling reactions, the first of which is completely regioselective, is of wide applicability and allows access to a large variety of derivatives. The absorption/emission and redox features, as well as the HOMO and LUMO energy levels, have been investigated; the results show that the optical and electronic properties can be tuned over a broad range. The diversity of the characteristics may be effectively exploited by using the thiophene-substituted 2-arylpyridines as ligands in cyclometalated sensitizers for dye-sensitized solar cells and other optoelectronic applications. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Two cyclometallated platinum(II) complexes, N^C^N-5-fluoro-1,3-di(2-pyridyl)benzene platinum(II) chloride, FPtCl, and N^C^N-5-methyl-1,3-di(2-pyridyl)benzene platinum(II) isothiocyanate, MePtNCS, have been synthesized and characterized. Both complexes are highly efficient phosphorescent green emitters which can also display excimer emission in the red region. They have been studied as triplet emitters in solution-processed, multilayer organic light-emitting diodes (OLEDs), together with the known complex of 5-methyl-1,3-di(2-pyridyl)benzene, MePtCl, for comparison. The trend in efficiencies of the OLEDs prepared correlates with the charge-trapping properties of the complexes. The most efficiently emitting complex, FPtCl, was used as the dopant in a solution-processed white OLED, employing monomer and excimer emission.

The luminescence and second order non linear optical (NLO) response of [Ir(ttpy)2(5-R-1,10-phen)][PF6] (ttpy = cyclometallated 3′-(2-pyridil)-2,2′:5′,2″-terthiophene, phen = phenanthroline; R = Me, NO2) and [Ir(pq)2(5-R-1,10-phen)][PF6] (pq = cyclometallated 2-phenylquinoline) have been investigated experimentally in CH2Cl2 solution and compared with that of [Ir(ppy)2(5-R-1,10-phen)][PF6] (ppy = cyclometallated 2-phenylpyridine), characterized by one of the highest second order NLO response ever reported for a metal complex. Substitution of ppy with the more π-delocalized pq does not affect significantly the luminescence and NLO properties. A slightly lower NLO response and a much poorer luminescence is observed for the related complexes with ttpy. In these complexes, DFT/TDDFT calculations show that the presence of ttpy induces a significant downshift of the HOMO energy, compared to ppy and pq. The NLO response is dominated by intense MLCT excited states, which are also assigned as originating the emission.

The reactivity of [Re(CO)5Cl] and [Re2(CO)10] with nucleophiles such as Me3SiO- and MeO- has been investigated by low-temperature NMR and by infrared spectroscopy particularly aimed at detecting the [Re(CO)5OR] species, which so far have eluded isolation, proposed as intermediates in the synthesis of the dimeric species [Re2(CO)6(mu-OR)3]- (R = SiMe3, Me). For both nucleophiles the first step involves an interaction with one specific carbonyl ligand and formation of new anionic complexes carrying a metal carboxy silyl or methyl ester, such as cis-[Re(CO)4(COOSiMe3)Cl]-, cis-[Re(CO)4(COOMe)Cl]-, [Re2(CO)9(COOSiMe3)]-, and [Re2(CO)9(COOMe)]-. The Re(I) complexes, stable only at low temperature, by further nucleophilic attack generate the well-known dimeric [Re2(CO)6(mu-OR)3]- complexes. The Re(0) metal carboxy-methyl esters derived from [Re2(CO)10] are thermally more stable and can be isolated in the solid state. In particular, the new complex [Re2(CO)9(COOMe)][NBu4] has been fully characterized by X-ray diffraction. In contrast, when the nucleophilic attack involves a weaker OR- nucleophile such as [(c-C6H11)7Si8O12O]- or a Re(I) pentacarbonyl substrate which bears a better leaving group such as the triflate, the low-temperature nucleophilic attack on a specific carbonyl ligand does not occur.

[Ir(cyclometallated 4,5-diphenyl-2-methyl-thiazole)(2)(5-R-1, 10-phenanthroline)][PF6] (R = CH3, NO2) complexes were prepared and fully characterized, the structure of the complex with 5-CH3-1, 10-phenanthroline being also determined by X-ray diffraction. The emission properties of both complexes have been investigated and their second-order nonlinear optical (NLO) response has been determined experimentally by the EFISH technique and found to be similar but slightly lower than that of related [Ir(ppy)(2)(5-R-1, 10-phenanthroline)][PF6] (ppy = cyclometallated 2-phenylpyridine), characterized by one of the highest second-order NLO response ever reported for a metal complex. In the complexes, SOS/TDDFT calculations show that the large and negative sign of the measured hyperpolarizability is mainly due to the significant contribution of rather intense MLCT transitions involving the phenanthroline as acceptor ligand. (C) 2008 Elsevier B.V. All rights reserved.

The photophysical and electrochemical properties of the novel complexes [Ir(ppy)(2)(5-X-1,10-phen)][PF(6)] (ppy = 2-phenylpyridine, phen = phenanthroline, X = NMe(2), NO(2)), [Ir(pq)(2)(5-X-1,10-phen)][PF(6)] (pq = 2-phenylquinoline, X = H, Me, NMe(2), NO(2)), [Ir(ppy)2(4-Me,7-Me-1,10-phen)][PF(6)], [Ir(ppy)2(5-Me,6-Me-1,10-phen)][PF(6)], [Ir(ppy)(2)(2-Me,9-Me-1,10-phen)][PF(6)], and [Ir(pq)2(4-Ph,7-Ph-1,10-phen)][PF(6)] have been investigated and compared with those of the known reference complexes [Ir(ppy)(2)(4-Me or 5-H or 5-Me-1,10-phen)][PF(6)] and [Ir(ppy)(2)(4-Ph,7-Ph-1,10-phen)][PF(6)], showing how the nature and number of the phenanthroline substituents tune the color of the emission, its quantum yield, and the emission lifetime. It turns out that the quantum yield is strongly dependent on the nonradiative decay. The geometry, ground state, electronic structure, and excited electronic states of the investigated complexes have been calculated on the basis of density functional theory (DFT) and time-dependent DFT approaches, thus substantiating the electrochemical measurements and providing insight into the electronic origin of the absorption spectra and of the lowest excited states involved in the light emission process. These results provide useful guidelines for further tailoring of the photophysical properties of ionic Ir(III) complexes.

[Ir(ppy)(2)(5-R-1,10-phen)][PF(6)] (ppy = cyclometallated 2-phenylpyridine, phen = phenanthroline, R = H, Me, NMe(2), NO(2)) and [Ir(ppy)(2)(4-R',7-R'-1,10-phen)][PF(6)] (R' = Me, Ph) complexes are characterized by one of the highest second order NLO response (measured by the EFISH technique) reported for a metal complex, mainly due (as suggested by a theoretical SOS-TDDFT investigation) to MLCT processes from the ppy-Ir based moiety acting as donor push system to pi* orbitals of phen, acting as an acceptor pull system; the good transparency to the second harmonic emission renders these NLO-phores appealing as building blocks for molecular materials with second harmonic generation.

The two-photon absorption (TPA) properties of various terpyridines of the kind [4'-(C6H4-(P)-X)2,2':6',2"-terpyridine] and related homoleptic and heteroleptic bis(terpyridine) cationic zinc(11) complexes were investigated by the TPA induced photoluminescence (TPA-PL) method in a femtosecond regime. It appeared that terpyridines bearing an X donor group are characterized by TPA cross sections among the largest ever reported for a molecule with a dipole symmetry whereas coordination to a Zn(II) center leads to a decrease of the TPA response.

[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).

The possibility to exploit a bottom-up approach to design and synthesize multichromophoric structures from a single molecular unit is strategic for the targeted synthesis of molecular compounds with well defined linear and nonlinear absorption properties. In this view, it is important to be able to predict the properties of multichromophoric units, based on the knowledge of the properties of the individual chromophores and their mutual arrangement. To this end, we present a combined experimental and theoretical study on 4-(para-di-n-butylaminostyryl)-pyridine, a push–pull molecule, and its dimer, 4, 4′-bis(para-di-n-butylaminostyryl)-2, 2′-bipyridine, formed by connecting the two pyridine groups into a bipyridine structure. One photon absorption and fluorescence spectra are measured in solvents of different polarity, and two-photon absorption spectra are recorded in dichloromethane. Experimental results are compared with results of TDDFT (Time-Dependent Density Functional Theory) and CIS (Configuration Interaction with Single excitation) methods implemented in the Gaussian03 program suite. An essential-state analysis of optical spectra is used to rationalize the observed behavior.

Various Ru(II) complexes with substituted 1,10-phenanthroline or 4,5-diazafluorene are characterized by a good to very large second order NLO response, as determined by EFISH. Among these complexes, [Ru(9-fulleriden-4,5-diazafluorene)(PPh(3))(2)Cl(2)] is particularly appealing due to its huge second-order NLO response and its transparency to the second harmonic generation. The structure of cis-Cl,trans-PPh(3)-[Ru(5-NO(2)-1,10-phen)(PPh(3))(2)Cl(2))] was determined by single-crystal X-ray diffraction.

[Ru3(CO)10Cl2], [Ru3(CO)12], [H4Ru4(CO)12], [H3Ru4(CO)12]-, [HRu6(CO)18]-, and [Ru6C(CO)16]2- have been synthesized in good or high yields by one-step or two-step (with the surface species [Ru(CO)3...

The synthesis of 4'-(C6H4-p-NBU2)-2,2':6',2" -terpyridine and the strongly enhanced second-order NLO response of its Zn(II), Ru(III) and Ir(III)complexes are reported, evidencing for the first time a shift from positive to negative value of the ligand quadratic hyperpolarizability by varying the nature of the metal centre. .