Ayele Teshome - Academia.edu (original) (raw)
Papers by Ayele Teshome
AIP Conference Proceedings, 2009
The synthesis of a series of new chromophores for nonlinear optics are described. Some of the com... more The synthesis of a series of new chromophores for nonlinear optics are described. Some of the compounds contain ``bulky'' groups designed to reduce aggregation between the molecules. While this may not impact on the electro-optic response of the compounds, both X-ray crystallographic and uv-vis spectroscopic studies indicate that such modifications will likely reduce aggregation once the chromophores are incorporated into
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 10, 2016
The molybdate-catalysed transfer hydrodeoxygenation (HDO) of benzyl alcohol to toluene driven by ... more The molybdate-catalysed transfer hydrodeoxygenation (HDO) of benzyl alcohol to toluene driven by oxidation of the solvent isopropyl alcohol to acetone has been investigated by using a combination of experimental and computational methods. A Hammett study that compared the relative rates for the transfer HDO of five para-substituted benzylic alcohols was carried out. Density-functional theory (DFT) calculations suggest a transition state with significant loss of aromaticity contributes to the lack of linearity observed in the Hammett study. The transfer HDO could also be carried out in neat PhCH2 OH at 175 °C. Under these conditions, PhCH2 OH underwent disproportionation to yield benzaldehyde, toluene, and significant amounts of bibenzyl. Isotopic-labelling experiments (using PhCH2 OD and PhCD2 OH) showed that incorporation of deuterium into the resultant toluene originated from the α position of benzyl alcohol, which is in line with the mechanism suggested by the DFT study.
ACS Catalysis, 2015
Chemical processes capable of reducing the high oxygen content of biomass-derived polyols are in ... more Chemical processes capable of reducing the high oxygen content of biomass-derived polyols are in demand in order to produce renewable substitutes for chemicals of fossil origin. Deoxydehydration (DODH) is an attractive reaction that in a single step transforms a vicinal diol into an alkene, but the reaction requires a homogeneous catalyst, a reductant, and a solvent, which are typically expensive, unsustainable, or inefficient. Herein, we present the use of molybdenum(VI)-based compounds, in particular the cheap and commercially available (NH 4) 6 Mo 7 O 24 ·4H 2 O, as catalysts for the DODH of vicinal diols in isopropyl alcohol (i PrOH), which serves as both the solvent and reductant. The reaction proceeds at 240−250 °C in a pressurized autoclave, and the alkene yield from simple aliphatic diols can be as high as 77%. The major byproducts are carbonyl compoundsformed by dehydration of the dioland the alcohols formed by transfer hydrogenation of the carbonyl compounds; the total yield of reduced species (i.e., alkene and alcohols) can be as high as 92%. The DODH of glycerol yields allyl alcohol, which undergoes subsequent Mo-catalyzed deoxygenation to propylene driven by the oxidation of i PrOH; a major byproduct is the homocoupled product 1,5-hexadiene. Further insight in this Mo-catalyzed deoxygenation is gained by an investigation of model compounds: The allylic alcohol 1-hexen-3-ol is deoxygenated to hexene isomers in a yield of 65%, while benzyl alcohol is deoxygenated to toluene in a yield of 93%. The DODH of erythritol yields 39% 2,5-dihydrofuran, while the DODH of the proposed intermediate 1,4-anhydroerythritol yields 75%. The mechanism of the DODH of 1,4-anhydroerythritol was investigated by means of density functional theory (DFT), and the rate-determining step (24.1 kcal/mol) was found to be reduction of a molybdenum(VI) diolate to a molybdenum(IV) diolate.
Bulletin of the Chemical Society of Ethiopia, 2006
Squalene, (2E, 7ξ,11ξ)-phyt-2-en-1-ol and amentoflavone have been isolated from the extract of th... more Squalene, (2E, 7ξ,11ξ)-phyt-2-en-1-ol and amentoflavone have been isolated from the extract of the leaves of Antidesma laciniatum. Their structures were elucidated using spectroscopic methods. This is the first report of these compounds from Antidesma species.
Optical Materials, Apr 1, 2010
The synthesis and linear and non-linear optical properties of a suite of chromophores containing ... more The synthesis and linear and non-linear optical properties of a suite of chromophores containing imine linkers between the donor and acceptor are described. The synthetic methodology allows for the smooth condensation of the precursor molecule N,N-dimethyl-p-nitrosoaniline with a variety of acceptors to afford the target chromophores in yields ranging from 52% to 85%. These molecules yield static first hyperpolarisability values, b (0) , of between 115 and 255 Â 10 À30 esu. As expected these values are influenced by both the strength of the acceptor unit as well as the likelihood of out of plane twisting within the chromophores.
Chemistry a European Journal, Jul 19, 2010
Journal of Organometallic Chemistry, Apr 1, 2008
The complexes [Fe{h-C 5 H 4 Ã/(E ) Ã/CH Ä/CHÃ/4-C 6 H 4 C Å/CX} 2 ] [X0/SiMe 3 (1), H (2), Au(PCy... more The complexes [Fe{h-C 5 H 4 Ã/(E ) Ã/CH Ä/CHÃ/4-C 6 H 4 C Å/CX} 2 ] [X0/SiMe 3 (1), H (2), Au(PCy 3 ) (3), Au(PPh 3 ) (4), Au(PMe 3 ) (5), RuCl(dppm) 2 (7), RuCl(dppe) 2 (8)] and [Fe{h-C 5 H 4 Ã/(E ) Ã/CH Ä/CHÃ/4-C 6 H 4 CH Ä/CRuCl(dppm) 2 } 2 ](PF 6 ) 2 (6) have been prepared and the identities of 1 and 7 confirmed by single-crystal X-ray structural studies. Complexes 1 Á/8 exhibit reversible oxidation waves in their cyclic voltammograms attributed to the Fe II/III couple of the ferrocenyl groups, 6 Á/8 also showing reversible (7, 8) or nonreversible (6) processes attributed to Ru-centered oxidation. Cubic nonlinearities at 800 nm by the Z-scan method are low for 1 Á/5; in contrast, complexes 6 and 7 exhibit large negative g real and large g imag values. A factor of 4 difference in jg j and two-photon absorption cross-section s 2 values for 6 and 7 suggest that they have potential as protically switchable NLO materials. #
Journal of Organometallic Chemistry, Apr 15, 2013
The synthesis of Ru(CThe syntheses and X-ray structural studies of Ru(C► Nonlinearities for ruthe... more The synthesis of Ru(CThe syntheses and X-ray structural studies of Ru(C► Nonlinearities for ruthenium alkynyl complexes are comparatively large with co-ligand dppf. ► Redox-active co-ligands such as dppf afford additional NLO redox-switching possibilities. ► TD-DFT studies reproduce trends in experimental linear and particularly nonlinear optical properties.
Optical Materials, 2010
The absorption and fluorescence spectral properties of several merocyanines with very high first ... more The absorption and fluorescence spectral properties of several merocyanines with very high first hyperpolarizabilities in fluid solutions are reported. These molecules contain a cyanodicyanomethylidenedihydrofuran electron acceptor group and with either a pyridinylidene or quinolinylidene electron donor. The molecules also contain a bulky substituent group which has been incorporated in order to hinder molecular aggregation. No effect of merocyanine concentration on the absorption spectral distributions of these compounds was observed in any of the solvents studied indicating there was no molecular aggregation in solution. The absorption spectra of these compounds display changes in their vibronic structure in solvents with different polarities/polarizabilities while the fluorescence spectra exhibit the standard solvent polarity stabilizing behaviour.
Linear and Nonlinear Optics of Organic Materials XI, 2011
The effect of extending the conjugation length, the deployment of various substituents and config... more The effect of extending the conjugation length, the deployment of various substituents and configurational locking of the polyene backbone on the second-order nonlinear optical (NLO) response of a series of indoline based compounds has been investigated. The ...
Inorganic Chemistry, 2009
The Journal of Physical Chemistry A, 2012
The structural and electronic properties of a highly solvatochromic merocyanine dye, 2-(3-cyano-5... more The structural and electronic properties of a highly solvatochromic merocyanine dye, 2-(3-cyano-5,5-dimethyl-4-(3-(1-octadecylpyridin-4(1H)-ylidene)prop-1-enyl)furan-2(5H)-ylidene)malononitrile (pyr3pi), have been investigated using UV-vis, NMR, hyper-Rayleigh scattering, and Raman spectroscopies and further interpreted using computational chemistry. Spectroscopic data indicate that pyr3pi exists in its zwitterionic form even in low polarity solvents with electronic absorption spectra showing a hypsochromic shift with an increase in solvent polarity and NMR experiments indicating an increasingly zwitterionic structure in chloroform as the temperature is lowered. Raman spectra in increasingly polar solvents show small variations of the structure that are consistent with a change toward a structure with more zwitterionic character. However, comparison of the calculated and experimental vibrational energies and intensities and comparison of NMR coupling constants with calculated bond order indicate that calculations underestimate the amount of charge separation seen in low polarity solvents. Although for this system density functional theory (DFT) calculations and the two-state model qualitatively reproduce negative solvatochromism, they fail to reproduce the trends in hyperpolarizability seen experimentally. This is attributed to solvent field DFT calculations underestimating the degree of charge separation in reaction fields representing low polarity solvents.
Polymer Bulletin, 1999
A simple method for the preparation of a suite of new nonlinear optical chromophores is presented... more A simple method for the preparation of a suite of new nonlinear optical chromophores is presented. Using this methodology we have been able to prepare chromophores with azo linkers and a variety of acceptor systems in high yields and without the need for chromatography. The compounds are highly solvatochromic, and the predicted values of their NLO response suggest they are candidates for further development.
Optical Materials, 2011
The synthesis, linear and second-order nonlinear optical (NLO) properties of a series of ionic in... more The synthesis, linear and second-order nonlinear optical (NLO) properties of a series of ionic indoline and N,N-dimethylaniline based chromophores are described. In order to optimise the second-order NLO response of these compounds four basic variations to the molecules and/or their environments have been implemented and their effect studied. These consist of changes to the counter-anion (from iodide to p-toluenesulfonate to naphthalene-2-sulfonate), variation of the solvent polarity [dimethyl sulfoxide (DMSO) to methanol (MeOH) to chloroform (CHCl 3 )], annelation of the acceptor unit (pyridinium to quinolinium) and a change in the donor used (N,N-dimethylaniline to indoline). It is found that the strongest enhancements to the quadratic NLO response occur when the acceptor moiety is changed from pyridinium to quinolinium, while compounds with an indoline donor group are slightly superior to those containing dimethylaniline as donor. There is no real discernable change in the first hyperpolarizability on altering either the counter-anion or solvent used for the measurements. X-ray crystallographic data were obtained for two of the compounds, and they are found to pack in centrosymmetric fashion, and have a small degree of twisting between the donor and acceptor. From this data it is seen that there is a general agreement between the degree of bond-length alternation (BLA) and the NLO response of the chromophores, and that for charged chromophores such as these a BLA value of approximately 0.1 Å is optimal.
Optical Materials, 2010
The synthesis and linear and non-linear optical properties of a suite of chromophores containing ... more The synthesis and linear and non-linear optical properties of a suite of chromophores containing imine linkers between the donor and acceptor are described. The synthetic methodology allows for the smooth condensation of the precursor molecule N,N-dimethyl-p-nitrosoaniline with a variety of acceptors to afford the target chromophores in yields ranging from 52% to 85%. These molecules yield static first hyperpolarisability values, b (0) , of between 115 and 255 Â 10 À30 esu. As expected these values are influenced by both the strength of the acceptor unit as well as the likelihood of out of plane twisting within the chromophores.
Optical Materials, 2009
The molecular linear and nonlinear optical (NLO) properties of a series of seven merocyanine dyes... more The molecular linear and nonlinear optical (NLO) properties of a series of seven merocyanine dyes have been studied in solvents covering a broad range of polarity (dioxane to dimethylsulfoxide). The benchmark for the series was the ''Right hand side" zwitterionic chromophore 1, with a short conjugation path and 4-pyridinylidene as the donor group. Optimization strategies to improve the nonlinear response involved an extension of the conjugation path (with one or two ethenyl groups), annelation (pyridine to quinoline), variation of the solvent polarity and partial ring locking of the p-conjugated system. All chromophores have as the acceptor moiety the cyanodicyanomethylidenedihydrofuran heterocycle. Optimising the NLO response of these zwitterionic dyes by decreasing the polarity of the solvent is only possible for the parent chromophore 1. This is because the three other successful strategies employed to further improve the second-order NLO response in polar media, result in detrimental aggregation in nonpolar media.
Journal of the American Chemical Society, 2009
The syntheses of trans-NO 2 }Cl(dppm) 2 ] (24) are reported, together with those of precursor alk... more The syntheses of trans-NO 2 }Cl(dppm) 2 ] (24) are reported, together with those of precursor alkynes, complexes with the donor-π-bridge-acceptor formulation that affords efficient quadratic and cubic NLO compounds; the identity of 19 was confirmed by a structural study. The electrochemical properties of 19-24 and related complexes with shorter π-bridge ligands were assessed by cyclic voltammetry, and the linear optical, quadratic nonlinear optical, and cubic nonlinear optical properties were assayed by UV-vis-NIR spectroscopy, hyper-Rayleigh scattering studies at 1064 and 1300 nm, and broad spectral range femtosecond Z-scan studies, respectively. The Ru II/III oxidation potentials and wavelengths of the optical absorption maxima decrease on π-bridge lengthening, until the tri(phenyleneethynylene) complex is reached, further chain lengthening leaving these parameters invariant; theoretical studies employing time-dependent density functional theory have shed light on this behavior. The quadratic nonlinearity 1064 and two-photon absorption cross-section reach maximal values at this same π-bridge length, a similar saturation behavior that may reflect a common importance of ruthenium-to-alkynyl ligand charge transfer in electronic and optical behavior in these molecules. (1) Organometallic Complexes for Nonlinear Optics. Part 44. Part 43: Rigamonti, L.; Babgi, B.; Cifuentes, M. P.; Roberts, R. L.; Petrie, S.; Stranger, R.; Righetto, S.; Teshome, A.; Asselberghs, I.; Clays, K.; Humphrey, M. G.
Journal of Applied Physics, 2005
We investigated second order optical nonlinearity of zinc oxide thin films, grown on glass substr... more We investigated second order optical nonlinearity of zinc oxide thin films, grown on glass substrates by the dual ion beam sputtering technique under different deposition conditions. Linear optical characterization of the films was carried out by spectrophotometric optical transmittance and reflectance measurements, giving the complex refractive index dispersion. Resistivity of the films was determined using the four-point probe sheet resistance method. Second harmonic generation measurements were performed by means of the Maker fringes technique where the fundamental beam was originated by nanosecond laser at = 1064 nm. We found a relatively high nonlinear optical response, and evidence of a dependence of the nonlinear coefficient on the deposition parameters for each sample. Moreover, the crystalline properties of the films were investigated by x-ray diffraction measurements and correlation with second order nonlinearity were analyzed. Finally, we investigated the influence of the oxygen flow rate during the deposition process on both the second order nonlinearity and the structural properties of the samples.
Inorganic Chemistry, 2009
Dyes and Pigments, 2013
ABSTRACT We report the synthesis of a series of nonlinear optical chromophores containing either ... more ABSTRACT We report the synthesis of a series of nonlinear optical chromophores containing either a dihydrobenzothiazolylidene or dihydroquinolinylidene donor with an azo linker. The results demonstrate the versatility of coupling a diazonium salt to a donor–methylidene nucleus in order to access novel materials with good thermal stabilities and high nonlinear optical responses. From hyper-Raleigh scattering studies it was found that the use of the well-known TCF acceptor yields the best performing chromophores, one of which has a dynamic first hyperpolarizability of 1900 × 10−30 esu at 800 nm. The results from this study suggest the use of pro-aromatic donors such as dihydrobenzothiazolylidene or dihydroquinolinylidene results in compounds with higher nonlinear optical responses than those containing donors based on either indoline or aniline.
AIP Conference Proceedings, 2009
The synthesis of a series of new chromophores for nonlinear optics are described. Some of the com... more The synthesis of a series of new chromophores for nonlinear optics are described. Some of the compounds contain ``bulky'' groups designed to reduce aggregation between the molecules. While this may not impact on the electro-optic response of the compounds, both X-ray crystallographic and uv-vis spectroscopic studies indicate that such modifications will likely reduce aggregation once the chromophores are incorporated into
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 10, 2016
The molybdate-catalysed transfer hydrodeoxygenation (HDO) of benzyl alcohol to toluene driven by ... more The molybdate-catalysed transfer hydrodeoxygenation (HDO) of benzyl alcohol to toluene driven by oxidation of the solvent isopropyl alcohol to acetone has been investigated by using a combination of experimental and computational methods. A Hammett study that compared the relative rates for the transfer HDO of five para-substituted benzylic alcohols was carried out. Density-functional theory (DFT) calculations suggest a transition state with significant loss of aromaticity contributes to the lack of linearity observed in the Hammett study. The transfer HDO could also be carried out in neat PhCH2 OH at 175 °C. Under these conditions, PhCH2 OH underwent disproportionation to yield benzaldehyde, toluene, and significant amounts of bibenzyl. Isotopic-labelling experiments (using PhCH2 OD and PhCD2 OH) showed that incorporation of deuterium into the resultant toluene originated from the α position of benzyl alcohol, which is in line with the mechanism suggested by the DFT study.
ACS Catalysis, 2015
Chemical processes capable of reducing the high oxygen content of biomass-derived polyols are in ... more Chemical processes capable of reducing the high oxygen content of biomass-derived polyols are in demand in order to produce renewable substitutes for chemicals of fossil origin. Deoxydehydration (DODH) is an attractive reaction that in a single step transforms a vicinal diol into an alkene, but the reaction requires a homogeneous catalyst, a reductant, and a solvent, which are typically expensive, unsustainable, or inefficient. Herein, we present the use of molybdenum(VI)-based compounds, in particular the cheap and commercially available (NH 4) 6 Mo 7 O 24 ·4H 2 O, as catalysts for the DODH of vicinal diols in isopropyl alcohol (i PrOH), which serves as both the solvent and reductant. The reaction proceeds at 240−250 °C in a pressurized autoclave, and the alkene yield from simple aliphatic diols can be as high as 77%. The major byproducts are carbonyl compoundsformed by dehydration of the dioland the alcohols formed by transfer hydrogenation of the carbonyl compounds; the total yield of reduced species (i.e., alkene and alcohols) can be as high as 92%. The DODH of glycerol yields allyl alcohol, which undergoes subsequent Mo-catalyzed deoxygenation to propylene driven by the oxidation of i PrOH; a major byproduct is the homocoupled product 1,5-hexadiene. Further insight in this Mo-catalyzed deoxygenation is gained by an investigation of model compounds: The allylic alcohol 1-hexen-3-ol is deoxygenated to hexene isomers in a yield of 65%, while benzyl alcohol is deoxygenated to toluene in a yield of 93%. The DODH of erythritol yields 39% 2,5-dihydrofuran, while the DODH of the proposed intermediate 1,4-anhydroerythritol yields 75%. The mechanism of the DODH of 1,4-anhydroerythritol was investigated by means of density functional theory (DFT), and the rate-determining step (24.1 kcal/mol) was found to be reduction of a molybdenum(VI) diolate to a molybdenum(IV) diolate.
Bulletin of the Chemical Society of Ethiopia, 2006
Squalene, (2E, 7ξ,11ξ)-phyt-2-en-1-ol and amentoflavone have been isolated from the extract of th... more Squalene, (2E, 7ξ,11ξ)-phyt-2-en-1-ol and amentoflavone have been isolated from the extract of the leaves of Antidesma laciniatum. Their structures were elucidated using spectroscopic methods. This is the first report of these compounds from Antidesma species.
Optical Materials, Apr 1, 2010
The synthesis and linear and non-linear optical properties of a suite of chromophores containing ... more The synthesis and linear and non-linear optical properties of a suite of chromophores containing imine linkers between the donor and acceptor are described. The synthetic methodology allows for the smooth condensation of the precursor molecule N,N-dimethyl-p-nitrosoaniline with a variety of acceptors to afford the target chromophores in yields ranging from 52% to 85%. These molecules yield static first hyperpolarisability values, b (0) , of between 115 and 255 Â 10 À30 esu. As expected these values are influenced by both the strength of the acceptor unit as well as the likelihood of out of plane twisting within the chromophores.
Chemistry a European Journal, Jul 19, 2010
Journal of Organometallic Chemistry, Apr 1, 2008
The complexes [Fe{h-C 5 H 4 Ã/(E ) Ã/CH Ä/CHÃ/4-C 6 H 4 C Å/CX} 2 ] [X0/SiMe 3 (1), H (2), Au(PCy... more The complexes [Fe{h-C 5 H 4 Ã/(E ) Ã/CH Ä/CHÃ/4-C 6 H 4 C Å/CX} 2 ] [X0/SiMe 3 (1), H (2), Au(PCy 3 ) (3), Au(PPh 3 ) (4), Au(PMe 3 ) (5), RuCl(dppm) 2 (7), RuCl(dppe) 2 (8)] and [Fe{h-C 5 H 4 Ã/(E ) Ã/CH Ä/CHÃ/4-C 6 H 4 CH Ä/CRuCl(dppm) 2 } 2 ](PF 6 ) 2 (6) have been prepared and the identities of 1 and 7 confirmed by single-crystal X-ray structural studies. Complexes 1 Á/8 exhibit reversible oxidation waves in their cyclic voltammograms attributed to the Fe II/III couple of the ferrocenyl groups, 6 Á/8 also showing reversible (7, 8) or nonreversible (6) processes attributed to Ru-centered oxidation. Cubic nonlinearities at 800 nm by the Z-scan method are low for 1 Á/5; in contrast, complexes 6 and 7 exhibit large negative g real and large g imag values. A factor of 4 difference in jg j and two-photon absorption cross-section s 2 values for 6 and 7 suggest that they have potential as protically switchable NLO materials. #
Journal of Organometallic Chemistry, Apr 15, 2013
The synthesis of Ru(CThe syntheses and X-ray structural studies of Ru(C► Nonlinearities for ruthe... more The synthesis of Ru(CThe syntheses and X-ray structural studies of Ru(C► Nonlinearities for ruthenium alkynyl complexes are comparatively large with co-ligand dppf. ► Redox-active co-ligands such as dppf afford additional NLO redox-switching possibilities. ► TD-DFT studies reproduce trends in experimental linear and particularly nonlinear optical properties.
Optical Materials, 2010
The absorption and fluorescence spectral properties of several merocyanines with very high first ... more The absorption and fluorescence spectral properties of several merocyanines with very high first hyperpolarizabilities in fluid solutions are reported. These molecules contain a cyanodicyanomethylidenedihydrofuran electron acceptor group and with either a pyridinylidene or quinolinylidene electron donor. The molecules also contain a bulky substituent group which has been incorporated in order to hinder molecular aggregation. No effect of merocyanine concentration on the absorption spectral distributions of these compounds was observed in any of the solvents studied indicating there was no molecular aggregation in solution. The absorption spectra of these compounds display changes in their vibronic structure in solvents with different polarities/polarizabilities while the fluorescence spectra exhibit the standard solvent polarity stabilizing behaviour.
Linear and Nonlinear Optics of Organic Materials XI, 2011
The effect of extending the conjugation length, the deployment of various substituents and config... more The effect of extending the conjugation length, the deployment of various substituents and configurational locking of the polyene backbone on the second-order nonlinear optical (NLO) response of a series of indoline based compounds has been investigated. The ...
Inorganic Chemistry, 2009
The Journal of Physical Chemistry A, 2012
The structural and electronic properties of a highly solvatochromic merocyanine dye, 2-(3-cyano-5... more The structural and electronic properties of a highly solvatochromic merocyanine dye, 2-(3-cyano-5,5-dimethyl-4-(3-(1-octadecylpyridin-4(1H)-ylidene)prop-1-enyl)furan-2(5H)-ylidene)malononitrile (pyr3pi), have been investigated using UV-vis, NMR, hyper-Rayleigh scattering, and Raman spectroscopies and further interpreted using computational chemistry. Spectroscopic data indicate that pyr3pi exists in its zwitterionic form even in low polarity solvents with electronic absorption spectra showing a hypsochromic shift with an increase in solvent polarity and NMR experiments indicating an increasingly zwitterionic structure in chloroform as the temperature is lowered. Raman spectra in increasingly polar solvents show small variations of the structure that are consistent with a change toward a structure with more zwitterionic character. However, comparison of the calculated and experimental vibrational energies and intensities and comparison of NMR coupling constants with calculated bond order indicate that calculations underestimate the amount of charge separation seen in low polarity solvents. Although for this system density functional theory (DFT) calculations and the two-state model qualitatively reproduce negative solvatochromism, they fail to reproduce the trends in hyperpolarizability seen experimentally. This is attributed to solvent field DFT calculations underestimating the degree of charge separation in reaction fields representing low polarity solvents.
Polymer Bulletin, 1999
A simple method for the preparation of a suite of new nonlinear optical chromophores is presented... more A simple method for the preparation of a suite of new nonlinear optical chromophores is presented. Using this methodology we have been able to prepare chromophores with azo linkers and a variety of acceptor systems in high yields and without the need for chromatography. The compounds are highly solvatochromic, and the predicted values of their NLO response suggest they are candidates for further development.
Optical Materials, 2011
The synthesis, linear and second-order nonlinear optical (NLO) properties of a series of ionic in... more The synthesis, linear and second-order nonlinear optical (NLO) properties of a series of ionic indoline and N,N-dimethylaniline based chromophores are described. In order to optimise the second-order NLO response of these compounds four basic variations to the molecules and/or their environments have been implemented and their effect studied. These consist of changes to the counter-anion (from iodide to p-toluenesulfonate to naphthalene-2-sulfonate), variation of the solvent polarity [dimethyl sulfoxide (DMSO) to methanol (MeOH) to chloroform (CHCl 3 )], annelation of the acceptor unit (pyridinium to quinolinium) and a change in the donor used (N,N-dimethylaniline to indoline). It is found that the strongest enhancements to the quadratic NLO response occur when the acceptor moiety is changed from pyridinium to quinolinium, while compounds with an indoline donor group are slightly superior to those containing dimethylaniline as donor. There is no real discernable change in the first hyperpolarizability on altering either the counter-anion or solvent used for the measurements. X-ray crystallographic data were obtained for two of the compounds, and they are found to pack in centrosymmetric fashion, and have a small degree of twisting between the donor and acceptor. From this data it is seen that there is a general agreement between the degree of bond-length alternation (BLA) and the NLO response of the chromophores, and that for charged chromophores such as these a BLA value of approximately 0.1 Å is optimal.
Optical Materials, 2010
The synthesis and linear and non-linear optical properties of a suite of chromophores containing ... more The synthesis and linear and non-linear optical properties of a suite of chromophores containing imine linkers between the donor and acceptor are described. The synthetic methodology allows for the smooth condensation of the precursor molecule N,N-dimethyl-p-nitrosoaniline with a variety of acceptors to afford the target chromophores in yields ranging from 52% to 85%. These molecules yield static first hyperpolarisability values, b (0) , of between 115 and 255 Â 10 À30 esu. As expected these values are influenced by both the strength of the acceptor unit as well as the likelihood of out of plane twisting within the chromophores.
Optical Materials, 2009
The molecular linear and nonlinear optical (NLO) properties of a series of seven merocyanine dyes... more The molecular linear and nonlinear optical (NLO) properties of a series of seven merocyanine dyes have been studied in solvents covering a broad range of polarity (dioxane to dimethylsulfoxide). The benchmark for the series was the ''Right hand side" zwitterionic chromophore 1, with a short conjugation path and 4-pyridinylidene as the donor group. Optimization strategies to improve the nonlinear response involved an extension of the conjugation path (with one or two ethenyl groups), annelation (pyridine to quinoline), variation of the solvent polarity and partial ring locking of the p-conjugated system. All chromophores have as the acceptor moiety the cyanodicyanomethylidenedihydrofuran heterocycle. Optimising the NLO response of these zwitterionic dyes by decreasing the polarity of the solvent is only possible for the parent chromophore 1. This is because the three other successful strategies employed to further improve the second-order NLO response in polar media, result in detrimental aggregation in nonpolar media.
Journal of the American Chemical Society, 2009
The syntheses of trans-NO 2 }Cl(dppm) 2 ] (24) are reported, together with those of precursor alk... more The syntheses of trans-NO 2 }Cl(dppm) 2 ] (24) are reported, together with those of precursor alkynes, complexes with the donor-π-bridge-acceptor formulation that affords efficient quadratic and cubic NLO compounds; the identity of 19 was confirmed by a structural study. The electrochemical properties of 19-24 and related complexes with shorter π-bridge ligands were assessed by cyclic voltammetry, and the linear optical, quadratic nonlinear optical, and cubic nonlinear optical properties were assayed by UV-vis-NIR spectroscopy, hyper-Rayleigh scattering studies at 1064 and 1300 nm, and broad spectral range femtosecond Z-scan studies, respectively. The Ru II/III oxidation potentials and wavelengths of the optical absorption maxima decrease on π-bridge lengthening, until the tri(phenyleneethynylene) complex is reached, further chain lengthening leaving these parameters invariant; theoretical studies employing time-dependent density functional theory have shed light on this behavior. The quadratic nonlinearity 1064 and two-photon absorption cross-section reach maximal values at this same π-bridge length, a similar saturation behavior that may reflect a common importance of ruthenium-to-alkynyl ligand charge transfer in electronic and optical behavior in these molecules. (1) Organometallic Complexes for Nonlinear Optics. Part 44. Part 43: Rigamonti, L.; Babgi, B.; Cifuentes, M. P.; Roberts, R. L.; Petrie, S.; Stranger, R.; Righetto, S.; Teshome, A.; Asselberghs, I.; Clays, K.; Humphrey, M. G.
Journal of Applied Physics, 2005
We investigated second order optical nonlinearity of zinc oxide thin films, grown on glass substr... more We investigated second order optical nonlinearity of zinc oxide thin films, grown on glass substrates by the dual ion beam sputtering technique under different deposition conditions. Linear optical characterization of the films was carried out by spectrophotometric optical transmittance and reflectance measurements, giving the complex refractive index dispersion. Resistivity of the films was determined using the four-point probe sheet resistance method. Second harmonic generation measurements were performed by means of the Maker fringes technique where the fundamental beam was originated by nanosecond laser at = 1064 nm. We found a relatively high nonlinear optical response, and evidence of a dependence of the nonlinear coefficient on the deposition parameters for each sample. Moreover, the crystalline properties of the films were investigated by x-ray diffraction measurements and correlation with second order nonlinearity were analyzed. Finally, we investigated the influence of the oxygen flow rate during the deposition process on both the second order nonlinearity and the structural properties of the samples.
Inorganic Chemistry, 2009
Dyes and Pigments, 2013
ABSTRACT We report the synthesis of a series of nonlinear optical chromophores containing either ... more ABSTRACT We report the synthesis of a series of nonlinear optical chromophores containing either a dihydrobenzothiazolylidene or dihydroquinolinylidene donor with an azo linker. The results demonstrate the versatility of coupling a diazonium salt to a donor–methylidene nucleus in order to access novel materials with good thermal stabilities and high nonlinear optical responses. From hyper-Raleigh scattering studies it was found that the use of the well-known TCF acceptor yields the best performing chromophores, one of which has a dynamic first hyperpolarizability of 1900 × 10−30 esu at 800 nm. The results from this study suggest the use of pro-aromatic donors such as dihydrobenzothiazolylidene or dihydroquinolinylidene results in compounds with higher nonlinear optical responses than those containing donors based on either indoline or aniline.