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NLO Response (nlo + response)

Distribution by Scientific Domains

Physics and Astronomy	25%

Selected Abstracts

The Role of Ion Pairs in the Second-Order NLO Response of 4-X-1-Methylpiridinium Salts,

CHEMPHYSCHEM, Issue 2 2010
Francesca Tessore Dr.
Abstract A series of 4-X-1-methylpyridinium cationic nonlinear optical (NLO) chromophores (X=(E)-CHCHC6H5; (E)-CHCHC6H4 -4,-C(CH3)3; (E)-CHCHC6H4 -4,-N(CH3)2; (E)-CHCHC6H4 -4,-N(C4H9)2; (E,E)-(CHCH)2C6H4 -4,-N(CH3)2) with various organic (CF3SO3,, p -CH3C6H4SO3,), inorganic (I,, ClO4,, SCN,, [Hg2I6]2,) and organometallic (cis -[Ir(CO)2I2],) 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 5×10,4,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. [source]

Synthesis of nonlinear optical polyimides containing azodiamine derivative chromophores and their electrooptic and thermal properties

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2002
Yuming Zhou
Abstract Some thermally stable second-order nonlinear optical (NLO) polyimides were synthesized. The polyimides were prepared by the ring-opening polyaddition of 4,4,-(hexafluoroisopropylidene) diphthalic anhydride and pyromellitic dianhydride with two aromatic azodiamine derivatives as the NLO chromophores. These chromophores, based on a nitro group connected with azobenzene as the acceptor end of a donor,,-bridge,acceptor chromophore and a diamine group as the donor end, had specific chemical stability. On the basis of ZERNER'S INDO methods, according to the sum-over-states formula, a program for the calculation of nonlinear second-order optical susceptibilities was devised. The resulting polyimides had high number-average and weight-average molecular weights of up to 26,000 and 53,500, respectively, and a large glass-transition temperature of 248 °C. With an in situ poling and temperature ramping technique, the optimal temperatures (Topt's) for corona poling were obtained for the largest second-order NLO response. The electrooptic coefficient (,33) of a polyimide at a wavelength of 830 nm was up to 21 pm/V after corona poling under its Topt, and the value remained at elevated temperatures (>90.6% was retained at 240 °C for >120 h). The thermal stability of the NLO polyimides was studied with UV spectrometry after poling of the films. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2478,2486, 2002 [source]

The role of the cyclometallated moiety on the second order nonlinear optical properties of cationic Ir(III) organometallic NLO-phores

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S1 2009
Claudia Dragonetti
Abstract The second order nonlinear optical (NLO) response of the new complexes [Ir(bzq)2(5-R-1,10-phen)][Y] (bzq = cyclometallated benzo[h]quinoline; phen = phenanthroline, R = Me, NO2; Y = PF6, C12H25SO3) and [Ir(bzq)2(4-R,7-R-1,10-phen)][Y] (R = Me, Ph) have been investigated experimentally by the Electric Field Induced Second Harmonic generation (EFISH) technique in CH2Cl2 solution and compared with that of [Ir(ppy)2(5-R-1,10-phen)][PF6] (ppy = cyclometallated 2-phenylpyridine, R = Me, NO2) and [Ir(ppy)2(4-R,7-R-1,10-phen)][PF6] (R = Me, Ph). It appeared that substitution of ppy with the more ,-delocalized bzq does not affect significantly the large second-order NLO response of this class of complexes. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The Role of Ion Pairs in the Second-Order NLO Response of 4-X-1-Methylpiridinium Salts,

Nonlinear Optical Properties of Ferrocene- and Porphyrin,[60]Fullerene Dyads

CHEMPHYSCHEM, Issue 7 2007
Evangelia Xenogiannopoulou Dr.
Abstract A series of novel [60]fullerene,ferrocene and [60]fullerene,porphyrin dyads, in which a fullerene and an electron donating moiety are attached through a flexible triethylene glycol linker are synthesized and their nonlinear optical (NLO) response studied. Specifically, the third-order susceptibility ,(3) of all fullerene derivatives are measured in toluene solutions by the optical Kerr effect (OKE) technique using 532 nm, 35 ps laser pulses and their second hyperpolarizability , are determined. All fullerene dyads studied exhibit enhancement of their NLO response compared to pristine fullerenes which has been attributed to the formation of a charge separated state. All experimentally measured hyperpolarizability , values are also calculated by the semiempirical methods AM1 and PM3. A good correlation is found between the theoretical and experimental values, suggesting that simple semiempirical methods can be employed for the designing and optimization of the fullerene-containing dyads displaying improved nonlinear responses. [source]

Bond models in linear and nonlinear optics

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2010
D. E. Aspnes
Abstract Atomic-scale descriptions of linear-optical properties such as reflection are nearly a century old, but surprisingly, analogous models describing nonlinear-optical (NLO) properties as the natural dynamic response of bond charges driven by an external field are a recent development. These bond-charge models have proven to be particularly useful in describing the relevant physics of second-, third-, and fourth-harmonic generation, identifying previously unrecognized contributions to NLO responses, and uncovering well-disguised correlations in tensor parameters determined phenomenologically from symmetry conditions. Current capabilities are discussed, and opportunities for improved understanding noted. [source]

Multichromophores for Nonlinear Optics: Designing the Material Properties by Electrostatic Interactions,

CHEMPHYSCHEM, Issue 17 2007
Francesca Terenziani Dr.
Abstract To fully exploit the promise of molecular materials for NLO applications, inter- and supramolecular interactions must be accounted for. We review our recent work on electrostatic interchromophore interactions in multichromophores for NLO applications. The discussion is based on a bottom-up modeling strategy: each chromophore is described in terms of an essential state model, validated and parameterized against spectroscopic data for solvated chromophores. The relevant information is then used to build a model for clusters of chromophores interacting through electrostatic forces. Exact NLO responses and spectra calculated within this model fully account for collective and cooperative interchromophore interactions, which can either amplify or suppress NLO responses; supramolecular engineering of multichromophores is a powerful tool for the design of NLO materials. Moreover, new features emerge in multichromophores with no counterpart at the single-chromophore level, offering new exciting opportunities for applications. [source]