Adriana Valore

Cyclometalated IrIII Complexes with Substituted 1,10‐Phenanthrolines: A New Class of Efficient Cationic Organometallic Second‐Order NLO Chromophores

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.

Cyclometallated platinum(II) complexes of 1,3-di(2-pyridyl)benzenes for solution-processable WOLEDs exploiting monomer and excimer phosphorescence

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.

Novel N^C^N-cyclometallated platinum complexes with acetylide co-ligands as efficient phosphors for OLEDs

Two new cyclometallated platinum(II) complexes have been prepared that incorporate a terdentate N^C^N-coordinating ligand and a monodentate acetylide co-ligand. The complexes, namely [PtL3–CC–C6H3F2] and [PtL6–CC–C6H3F2] (where HL3 = 5-methyl-1,3-di(2-pyridyl)benzene; HL6 = 5-mesityl-1,3-di(2-pyridyl)benzene; H–CC–C6H3F2 = 3,5-difluorophenylacetylene), were prepared by ligand metathesis from the corresponding chloro complex PtLnCl. Both of the new complexes are intensely luminescent in solution, displaying quantum yields superior to PtLnCl. OLEDs have been prepared using the new compounds as phosphorescent emitters. Although both lead to efficient devices, the best electroluminescence quantum efficiencies are obtained with the derivative of HL6, having the mesityl group on the cyclometallated phenyl ring. The superior performance with this complex can be rationalised in terms of the greater steric hindrance that serves to reduce aggregate-induced quenching.

Fluorinated β-Diketonate Diglyme Lanthanide Complexes as New Second-Order Nonlinear Optical Chromophores: The Role of f Electrons in the Dipolar and Octupolar Contribution to Quadratic Hyperpolarizability

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 beta(HLS), which is dominated by an octupolar contribution, is much lower along the Ln series. Remarkably, the good beta(HLS) values of these simple systems, well known for their luminescence properties, are reached at no cost of transparency.

Thiocyanate-Free Ruthenium(II) Sensitizer with a Pyrid-2-yltetrazolate Ligand for Dye-Sensitized Solar Cells

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.

Linear and nonlinear optical properties of tris-cyclometalated phenylpyridine Ir(III) complexes incorporating π-conjugated substituents.

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.

Platinum(II) complexes with cyclometallated 5-π-delocalized-donor-1,3-di(2-pyridyl)benzene ligands as efficient phosphors for NIR-OLEDs

Two new pincer proligands, namely 5-(p-(N,N-diphenylamino)phenylethynyl)-1,3-di(2-pyridyl)benzene (HL1) and trans-5-(p-(N,N-diphenylamino)styryl-1,3-di(2-pyridyl)benzene (HL2) were prepared together with their N^C^N-coordinated cyclometallated platinum(II) complexes PtL1X (X = Cl, NCS) and PtL2Cl. Both ligands are intensely luminescent in solution (quantum yields > 0.8). PtL1X complexes display high quantum yields in solution whereas that of PtL2Cl is very low due to the ease with which trans to cis isomerisation of the diphenylaminostyryl CC bond occurs. Distinct sets of emission bands attributable to the cis and trans forms are observable in glass at 77 K, the assignments being supported by TD-DFT calculations. Organic light-emitting diodes (OLEDs) have been prepared using the new compounds as phosphorescent emitters. Remarkably, despite the inferior quantum yield of PtL2Cl in solution, the best electroluminescence quantum efficiencies are obtained with this complex, which emerges as an excellent candidate for the preparation of NIR-OLEDs.

Thiocyanate-free cyclometalated ruthenium sensitizers for solar cells based on heteroaromatic-substituted 2-arylpyridines

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.

Tuning the Dipolar Second‐Order Nonlinear Optical Properties of Cyclometalated Platinum(II) Complexes with Tridentate N^C^N Binding Ligands

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.

Optoelectronic properties of OLEC devices based on phenylquinoline and phenylpyridine ionic iridium complexes

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)]).