Elena Cariati

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.

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.

Polymorphism-dependent aggregation induced emission of a push-pull dye and its multi-stimuli responsive behavior†

A comprehensive optical investigation of 1,1-dicyano-2,2-bis(4-dimethylaminophenyl)ethylene (1) is presented. The compound crystallizes in four different forms all displaying AIE behavior. The crystalline forms A and B are yellow-orange-emissive, while C and D are green-emissive. On the basis of X-ray structural analysis, the weak intermolecular interactions account for restricted internal rotations, leading to fluorescence enhancement in the crystals; however, the difference in emission color is ascribed to the various conformations of the molecules in the four crystalline forms. In addition, the emission color of crystals of A can be tuned by heating and grinding, that of B by grinding only, while crystals of C show chronochromic behavior. An explanation for such a rich variety of luminescence behavior is formulated here through the use of steady state and time resolved photoluminescence, X-ray diffraction analysis and DFT and TDDFT calculations. The involved chromic mechanism appears to be mainly associated with surface defects induced by the external stimuli rather than an amorphization process, as frequently observed for other stimuli responsive compounds.

An acido-triggered reversible luminescent and nonlinear optical switch based on a substituted styrylpyridine: EFISH measurements as an unusual method to reveal a protonation-deprotonation NLO contrast†

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.

Slow relaxation of the magnetization in non-linear optical active layered mixed metal oxalate chains.

New Co(II) members of the family of multifunctional materials of general formula [DAMS](4)[M(2)Co(C(2)O(4))(6)]·2DAMBA·2H(2)O (M(III) = Rh, Fe, Cr; DAMBA = para-dimethylaminobenzaldehyde and [DAMS(+)] = trans-4-(4-dimethylaminostyryl)-1-methylpyridinium) have been isolated and characterized. Such new hybrid mixed metal oxalates are isostructural with the previously investigated containing Zn(II), Mn(II), and Ni(II). This allows to preserve the exceptional second harmonic generation (SHG) activity, due to both the large molecular quadratic hyperpolarizability of [DAMS(+)] and the efficiency of the crystalline network which organizes [DAMS(+)] into head-to-tail arranged J-type aggregates, and to further tune the magnetic properties. In particular, the magnetic data of the Rh(III) derivative demonstrate that high spin octacoordinated Co(II) centers behave very similarly to the hexacoordinated Co(II) ones, being dominated by a large orbital contribution. The Cr(III) derivative is characterized by ferromagnetic Cr(III)-Co(II) interactions. Most relevantly, the Fe(III) compound is characterized by a moderate antiferromagnetic interaction between Fe(III) and Co(II), resulting in a ferrimagnetic like structure. Its low temperature dynamic magnetic properties were found to follow a thermally activated behavior (τ(0) = 8.6 × 10(-11) s and ΔE = 21.4 K) and make this a candidate for the second oxalate-based single chain magnet (SCM) reported up to date, a property which in this case is coupled to the second order non linear optical (NLO) ones.

H-Aggregates Granting Crystallization-Induced Emissive Behavior and Ultralong Phosphorescence from a Pure Organic Molecule

Solid-state luminescent materials with long lifetimes are the subject of ever-growing interest from both a scientific and a technological point of view. However, when dealing with organic compounds, the achievement of highly efficient materials is limited by aggregation-caused quenching (ACQ) phenomena on one side and by ultrafast deactivation of the excited states on the other. Here, we report on a simple organic molecule, namely, cyclic triimidazole (C9H6N6), 1, showing crystallization-induced emissive (CIE) behavior and, in particular, ultralong phosphorescence due to strong coupling in H-aggregated molecules. Our experimental data reveal that luminescence lifetimes up to 1 s, which are several orders of magnitude longer than those of conventional organic fluorophores, can be realized under ambient conditions, thus expanding the class of organic materials for phosphorescence applications.

Reproducible high-yield syntheses of [Ru3(CO)12], [H4Ru4(CO)12], and [Ru6C(CO)16]2− by a convenient two-step methodology involving controlled reduction in ethylene glycol of RuCl3·nH2O

Abstract [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.

High-yield syntheses, under mild conditions, of various neutral and anionic ruthenium and osmium carbonyl clusters by controlled reduction in ethylene glycol of [M(CO)3Cl2]2 or MCl3 (MRu, Os) in the presence of Na2CO3 or K2CO3 ☆

Abstract [M 3 (CO) 12 ], [H 4 M 4 (CO) 12 ], [H 3 M 4 (CO) 12 ] − (MRu, Os) and [Ru 6 C(CO) 16 ] 2− have been synthesized in high yields by one-pot controlled reduction at atmospheric pressure of MCl 3 or [M(CO) 3 Cl 2 ] 2 , dissolved in t -amyl alcohol or ethylene glycol, working in the presence of alkali carbonates. The selectivity of the reduction is controlled by the: (i) nature and quantity of the alkali carbonate (Na 2 CO 3 or K 2 CO 3 ); (ii) nature of the solvent; (iii) gas-phase composition (CO or CO+H 2 ); (iv) temperature and (v) reaction time. Yields are so high and reaction conditions so mild that, in most cases, these new syntheses are more convenient than those previously reported either in solution or on the silica surface as reaction medium.

Fluorine-induced J-aggregation enhances emissive properties of a new NLO push–pull chromophore

A new fluorinated push–pull chromophore with good second-order NLO properties even in concentrated solution shows solid state intermolecular aryl–fluoroaryl interactions leading to J-aggregates with intense solid state luminescence.

LUMINESCENCE RESPONSE OF THE SOLID STATE POLYNUCLEAR COPPER(I) IODIDE MATERIALS CUI(4-PICOLINE)X TO VOLATILE ORGANIC COMPOUNDS

Exposure of the polymeric solid [CuI(4-pic)]∞ to either liquid or vapor toluene leads to disappearance of this material’s characteristic room temperature blue emission (λmax 437 nm) and the appearance of the yellow emission (λmax 580 nm) indicative of the [CuI(4-pic)]4 tetramer; the process is reversed when the latter is exposed to liquid or vapor n-pentane.