Intramolecular Cooperative Effects in Multichromophoric Cavitands Exhibiting Nonlinear Optical Properties

We report on the design, synthesis, and characterization of a new class of multichromophoric cavitands based on resorcin[4]arenes. The novel compounds have exhibited high values of second-order nonlinear optical (NLO) properties, as evidenced by electric-field-induced second harmonic generation (EFISHG) measurements. Theoretical calculations indicate the presence of edge-to-face T-shaped interactions between the aromatic building blocks within these multichromophoric systems, which is further supported by the detection of hypsochromic shifts in UV-vis and upfield aromatic chemical shifts in 1H NMR. We proved for the first time that the gain in the quadratic hyperpolarizabilities of multichromophoric NLO macrocycles, originating from the near parallel orientations of the subchromophores, can be partially suppressed if the distance between the dipolar subunits falls into a specific range, where intramolecular cooperative and/or collective effects are operative. Our finding will contribute to the better understanding of the phenomenon of cooperativity in new molecular materials with promising NLO properties. (Figure Presented). © 2015 American Chemical Society

Spectral and nonlinear optical studies of Propane-1, 3-diaminium nitrate

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Palladium-catalyzed cross-coupling reaction of a chiral ferrocenyl zinc reagent with aromatic bromides: Application to the design of chiral octupoles for second harmonic generation

Palladium catalyzed cross coupling reaction of a chiral ferrocenylzinc reagent with aryl bromides allowed the introduction of a planary chiral ferrocenyl subunit on an aryl fragment. Using this method, new C-3 symmetric chiral architecture bearing organometallic donor-acceptor fragments were assembled starting from a common tris aldehyde precursor. The non-linear optical properties were measured using the Harmonic Light Scattering method and the potentiality for the new chromophores to behave as octupoles is also discussed

Photobleaching of nonlinear organic co-crystals 2,6-diaminopyridine-4-nitrophenol-4-nitrophenolate

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The relevance of the octupolar contribution to the quadratic hyperpolarizability of dipolar neutral Ir(III), Pt(II) and Ru(II) complexes

Various neutral dipolar Ir(III), Pt(II) and Ru(II) complexes characterized by a high \u3bc\u3b2 1.907 value, as determined by the Electric Field Induced Second Harmonic generation (EFISH) technique, show a large , as determined by the Harmonic Light Scattering (HLS) technique. A combination of both techniques is used to evaluate the dipolar and octupolar contributions to the total quadratic hyperpolarizability, putting in evidence that the major contribution is controlled by the octupolar part

Infrared emissions, visible up-conversion, thermoluminescence and defect centres in Er(3)Al(5)O(12) phosphor obtained by solution combustion reaction

The Er(3)Al(5)O(12) phosphor powders were prepared using the solution combustion method. Formation and homogeneity of the Er(3)Al(5)O(12) phosphor powders have been verified by X-ray diffraction and energy-dispersive X-ray analysis respectively. The frequency up-conversion from Er(3)Al(5)O(12) phosphor powder corresponding to the (2)H(9/2) -> (4)I(15/2), (2)H(11/2) -> (4)I(15/2), (4)S(3/2) -> (4)I(15/2), (4)F(9/2) -> (4)I(15/2) and the infrared emission (IR) due to the (4)I(13/2) -> (4)I(15/2) transitions lying at similar to 410, similar to 524, similar to 556, 645-680 nm and at similar to 1.53 mu m respectively upon excitation with a Ti-Sapphire pulsed/CW laser have been reported. The mechanism responsible for the frequency up-conversion and IR emission is discussed in detail. Defect centres induced by radiation were studied using the techniques of thermoluminescence and electron spin resonance. A single glow peak at 430A degrees C is observed and the thermoluminescence results show the presence of a defect center which decays at high temperature. Electron spin resonance studies indicate a center characterized by a g-factor equal to 2.0056 and it is observed that this center is not related to the thermoluminescence peak. A negligibly small concentration of cation and anion vacancies appears to be present in the phosphor in accordance with the earlier theoretical predictions.FAPESP, BrazilFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Effect of the coordination to M(II) metal centers (M = Zn, Cd, Pt) on the quadratic hyperpolarizability of various substituted 5-X-1,10-phenanthrolines (X = donor group) and of trans-4-(dimethylamino)-4 '-stilbazole

Coordination to a Zn(II) center of chelating pi-delocalized nitrogen donor ligands such as 5-X-1,10-phenanthrolines (X = OMe, NMe2, trans-CH=CHC6H4-4'-NMe2, trans, trans-(CH=CH)(2)C6H4-4'-NMe2) produces a significant enhancement of their quadratic hyperpolarizability measured either by the EFISH technique (beta(1.34)) or by absorption and emission solvatochromic investigations (beta(CT)) working with an incident wavelength of 1.34 mum. However, the enhancement factor by metal coordination of the quadratic hyperpolarizability of planar 5-X-1,10-phenanthrolines is lower than that of the nonplanar and flexible ligand 4-(p-(dibutylamino)styryl)-4'-methyl-2,2'-bipyridine because this latter ligand becomes planar and rigid by coordination. Coordination of 5-(trans-CH=CHC6H4-4'-NMe2)-1,10-phenanthroline to the softer Cd(CH3CO2)(2) does not produce an enhancement of the quadratic hyperpolarizability. This is due to a significant decrease of Deltamu(eg) (difference of the dipole moment in the excited and ground states of the intraligand charge transfer (ILCT)) upon coordination to the Cd(II) center. Strangely enough, the second-order NLO response of Zn(II) and Pt(II) complexes carrying two 4-trans-NC5H4CH=CHC6H4-4'-NMe2 stilbazole ligands in a tetrahedral or planar coordination indicates a significant increase, upon coordination, of the quadratic hyperpolarizability beta(CT), along the ILCT transition of the ligand, but an irrelevant increase of beta(1.34), which is the vectorial component of the tensor beta along the molecular dipole moment axis, although in the free ligand both beta(CT) and beta(1.34) are comparable. The lack of coincidence of the molecular dipole moment axis with the direction of the ILCT transition of the ligand, a major origin of the second-order NLO response, could explain why beta(CT) and beta(1.34) values are not comparable. In fact, a detailed solvatochromic analysis shows that the increase of beta(CT) upon coordination to Zn(II) or Pt(II) of the single stilbazole ligand is not significant, in agreement with EFISH measurements and the irrelevant red shift of the ILCT transition

Infrared luminescence, thermoluminescence and defect centres in Er and Yb co-doped ZnAl(2)O(4) phosphor

Er and Yb co-doped ZnAl(2)O(4) phosphors were prepared by solution combustion synthesis and the identification of Er and Yb were done by energy-dispersive X-ray analysis (EDX) studies. A luminescence at 1.5 mu m, due to the (4)I(13/2) ->(4)I(15/2) transition, has been studied in the NIR region in Er and Yb co-doped ZnAl(2)O(4) phosphors upon 980 nm CW pumping. Er-doped ZnAl(2)O(4) exhibits two thermally stimulated luminescence (TSL) peaks around 174A degrees C and 483A degrees C, while Yb co-doped ZnAl(2)O(4) exhibits TSL peaks around 170A degrees C and 423A degrees C. Electron spin resonance (ESR) studies were carried out to identify defect centres responsible for TSL peaks observed in the phosphors. Room temperature ESR spectrum appears to be a superposition of two distinct centres. These centres are assigned to an O(-) ion and F(+) centre. O(-) ion appears to correlate with the 174A degrees C TSL peak and F(+) centre appears to relate with the high temperature TSL peak at 483A degrees C in ZnAl(2)O(4):Er phosphor.Seoul R&D program (2006)Seoul R&D program (2006)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP, Brazi