Victor Hernandez - Academia.edu (original) (raw)
Talks by Victor Hernandez
Papers by Victor Hernandez
Radical cations of a heptathienoacene a,b-substituted with four n-decyl side groups (D4T7C + ) fo... more Radical cations of a heptathienoacene a,b-substituted with four n-decyl side groups (D4T7C + ) form exceptionally stable p-dimer dications already at ambient temperature (Chem. Comm. 2011, 47, 12622). This extraordinary p-dimerization process is investigated here with a focus on the ultimate [D4T7C + ] 2 p-dimer dication and yet-unreported transitory species formed during and after the oxidation. To this end, we use a joint experimental and theoretical approach that combines cyclic voltammetry, in situ spectrochemistry and spectroelectrochemistry, EPR spectroscopy, and DFT calculations. The impact of temperature, thienoacene concentration, and the nature and concentration of counteranions on the p-dimerization process is also investigated in detail.
J Phys Chem a, 2005
A series of R,ω-bis(mesitylthio)oligothiophenes of various chain lengths and with different side ... more A series of R,ω-bis(mesitylthio)oligothiophenes of various chain lengths and with different side substitution patterns have been studied in their oxidized states by means of electron absorption and Raman spectroscopies in combination with theory in the framework of the density functional theory. Upon chemical oxidation, stable radical cations, dications, and even radical trications are generated. Longer chain lengths better stabilize higher oxidation states. The tetramer can be easily converted to the dication, and a trication can be obtained for the ethylenedioxy derivative. The R,ω-sulfur atoms are actively involved in the formation of the charged species and exert a favorable tuning of their electronic structure. Raman spectra provide experimental evidence of the attainment of quinoidal structures within the conjugated path, initially heteroaromatic, with different extension as a function of the p-doping level.
El 60% de la producción mundial de frijol (Phaseolus vulgaris L.) se obtiene en condiciones de dé... more El 60% de la producción mundial de frijol (Phaseolus vulgaris L.) se obtiene en condiciones de déficit hídrico, por lo que este factor es el que más contribuye en la reducción del rendimiento después de las enfermedades . Entre las respuestas fisiológicas de las plantas al estrés hídrico está la disminución de la conductancia estomática Pattanagul y Madore, 1999) que causa reducción de la transpiración y de la fotosíntesis Pattanagul y Madore, 1999). La fotosíntesis en estrés hídrico también declina debido a la reducción en la fijación de C total (Brevedan y Egli, 2003), al daño en la maquinaria biosintética requerida para la asimilación de C y para su conversión a productos metabólicamente utilizables (Pattanagual y Madore, 1999). El déficit hídrico provoca además pérdida de reservas de almidón y de azúcares no estructurales que soportan el crecimiento y desarrollo, por la disminución en la actividad de la enzima fotosintética galactinol sintasa (Pattanagul y Madore, 1999).
Theoretical Chemistry Accounts, 2011
This work presents an analysis of the evolution of the molecular, vibrational and optical propert... more This work presents an analysis of the evolution of the molecular, vibrational and optical properties of a family of functionalized pentacenes. The analysis is performed on the basis of DFT quantum-chemical calculations in combination with spectroscopic techniques (Raman and UV-Vis). Theoretical calculations show that the bond length C-C/C=C alternation along the peripheral oligoenic ribbons increases with electron-releasing dioxolane substituents and diminishes with electron-withdrawing chlorine atoms and cyano groups. The attachment of triisopropylsilylethynyl groups increases the complexity of the Raman spectra. The spectra present many intense features of similar intensities in the 1,200-1,600 cm -1 range which are described by a combination of C-C/C=C stretching vibrations and in-plane C-H deformations spreading over the whole pentacene backbone. The absorption spectra display absorption bands in three different energy regions of the UV-Vis electromagnetic range. The spectra are dominated by a strong absorption band measured in the 300-350 nm region, which undergoes a sizeable red-shift with the substitution pattern, and a low-intensity, three-peak band in the 500-700 nm region, which undergoes a blue-or a red-shift depending on the electronic nature of the substituents. TDDFT calculations enable a detailed description of the trends observed in the absorption spectra.
Opt Mater, 1999
We present the results of an FT-IR and FT-Raman vibrational spectroscopic study carried out on α,... more We present the results of an FT-IR and FT-Raman vibrational spectroscopic study carried out on α, α'-diethylquinquethiophene and α, α'-diethylsexithiophene upon doping with iodine vapours and nitrosyl salts. The wavenumbers and intensity dispersions observed for the doping induced Raman bands with the oxidation degree are utilized to elucidate the conjugational defect-type. The near-infrared Raman spectra indicate the existence of radical cations and dications as the major oxidized species in the I 2-doped and NO-doped oligomers, respectively.
J Phys Chem B, 2002
In this paper, we investigate the vibrational properties of a novel family of amorphous molecular... more In this paper, we investigate the vibrational properties of a novel family of amorphous molecular materials containing an end-capped oligothiophene backbone of variable length, R,R′-bis-{4-[bis(4-methylphenyl)amino]-phenyl}-oligothiophene, which function as color-tunable emitting materials for organic light-emitting diodes. The advantage of these amorphous oligothiophenes with respect to their crystalline parents is that the fluorescence quantum efficiencies as thin films are quite similar to those commonly found in solution. The thorough analysis of the infrared and Raman spectra of the neutral materials as solids has revealed the uselfulness and selectivity of Raman spectroscopy to determine the efficiency of the π conjugation. Density functional theory B3LYP/3-21G* calculations rendered largely distorted conformations of the 4-[bis(4methylphenyl)amino]phenyl groups with respect to the thiophene rings least-squares plane, in full accordance with the amorphous nature of the materials. The infrared and Raman spectra of the materials recorded at different temperatures between -170 and +160°C did not show any substantial change, thus indicating that the materials have a high thermal stability, which has significance for their use as active components in optoelectronic devices.
![Research paper thumbnail of Computation and Spectroelectrochemistry as Complementary Tools for the Study of Electrochemically Induced Charged Defects in 4-[ Bis(4-methylphenyl)amino]phenyl Oligothiophenes as Model Systems for Hole-Transporting Materials](https://attachments.academia-assets.com/54406593/thumbnails/1.jpg)
](J Phys Chem B, 2003
The in situ electronic absorption and Fourier transform Raman scattering spectra recorded during ... more The in situ electronic absorption and Fourier transform Raman scattering spectra recorded during the electrochemical oxidation of two R,R′-end-capped 4-[bis(4-methylphenyl)amino]phenyl oligothiophenes with three and four thiophene rings are reported. We have characterized a radical cation and a dication species in the trimer and up to a radical trication in the tetramer. The electronic and the Raman spectra have been interpreted and assigned with the final goal of obtaining structural information about the contribution of the bis(4-methylphenyl)amino groups, the innermost phenyl rings, and the central thienyl chain length to the stabilization of the electrochemically induced charged defects. The experimental data have been supported by theoretical calculations in the framework of the density functional theory. The charged defects can be viewed as models of hole carriers or photoexcitons in real devices.
In this work, we present a comparative study of the second order nonlinear optical properties of ... more In this work, we present a comparative study of the second order nonlinear optical properties of a series of chromophores containing a fused terthiophene, namely dithienothiophene (DTT), as electron relay with either D-π-A or D-π-D substitution patterns. The effect of the acceptor/donor strength and the solvent polarity confirm the possibility of fine-tuning optical non-linearities in the asymmetric samples. The geometrical and electronic properties calculated in solution reveal that push-pull chromophores become highly polarized as the dielectric constant of the solvent increases. Theoretical NLO calculations furthermore reveal a moderate nonlinear optical activity for the symmetric samples.
Chemistry of Materials, Oct 20, 2008
Electrochemical oxidation of bis-terthienyl-B (B ) ethane, disulfide, diacetylene, acetylene, eth... more Electrochemical oxidation of bis-terthienyl-B (B ) ethane, disulfide, diacetylene, acetylene, ethylene) has been investigated. Monomers without and with 3,3′′-dialkylsubstitution are regularly coupled to polymers alternating sexithiophene and B moieties. The corresponding terthienyl homopolymers have also been produced for comparison. The polymers obtained are characterized by cyclic voltammetry, EQCM, UV-vis, and FTIR spectroscopy, in situ ESR and in situ conductivity. The conductivities of p-doped polymers with ethane or disulfide bridges fall in a narrow range (1-5 × 10 -2 S cm -1 ) and are practically the same as those of R,ω-dimethylsexithiophene (1 × 10 -2 S cm -1 ), suggesting that conduction proceeds without the help of the links via a direct redox hopping between sexithiophene blocks of adjacent polymer chains. In the cases of diacetylene and acetylene, conduction changes from redox to bipolarontype but only in the case of ethylene the conductivity jumps to high values (1-5 S cm -1 ) corresponding to those of the polymers without the bridging moiety B, i.e., with shortened thiophene rings. DFT calculations of the bridge energy levels account for this result. (1) Walzer, K.; Maennig, B.; Pfeiffer, M.; Leo, K. Chem. ReV. 2007, 107, 1233. (2) (a) Kline, R. J.; McGehee, M. D.; Kadnikova, E. N.; Liu, J.; Frechet, J. M. J. AdV. Mater. 2003, 15, 1519. (b) Ong, B. S.; Wu, Y.; Liu, P.; Gardner, S. J. Am. Chem. Soc. 2004, 126, 3378. (3) Li, G.; Shrotriya, V.; Huang, J.; Yao, Y.; Moriarty, T.; Emery, K.; Yang, Y. Nat. Mater. 2005, 864. (4) Harima, Y.; Kim, D.-H.; Tsutitori, Y.; Jiang, X.; Patil, R.; Ooyama, Y.; Ohshita, J.; Kunai, A. Chem. Phys. Lett. 2006, 420, 387. (5) Zotti, G.; Schiavon, G.; Berlin, A.; Pagani, G. AdV. Mater. 1993, 5, 551. (6) Zotti, G.; Zecchin, S.; Vercelli, B.; Berlin, A.; Grimoldi, S.; Pasini, M. C.; Raposo, M. M. M. Chem. Mater. 2005, 17, 6492. (7) Zotti, G.; Zecchin, S.; Vercelli, B.; Pasini, M.; Destri, S.; Bertini, F.;
Portugaliae Electrochimica Acta, 2010
Journal of Molecular Structure, 2000
This paper reports results of a theoretical study about the effect of ionization on the infrared ... more This paper reports results of a theoretical study about the effect of ionization on the infrared and Raman spectra of a,a Hbis(aminomethyl)quaterthiophene with the objective of obtaining a deeper insight into the geometry and spectral changes occurring upon doping of the oligothiophenes and polythiophene. For these purposes, we determine the structures, vibrational frequencies and infrared intensities of the neutral compound and of its radical cation and dication. Ab initio calculations, at the B3LYP/6-31G ءء and RHF/6-31G ءء levels of theory, are employed to assess the structural and spectral information for the neutral and charged states. ᭧
J Liq Chromatogr Relat Techno, 1993
A comprehensive study of the reaction between Purpald (4-amino-3- hydrazino-5-mercapto-l, 2, 4-tr... more A comprehensive study of the reaction between Purpald (4-amino-3- hydrazino-5-mercapto-l, 2, 4-triazole) and eight neutral monosaccharides in order to establish the optimal conditions (wavelength, oxygen supply, temperature, time, pH and concentration range) was carried out. The reaction was applied to the post-column detection in HPLC of monosaccharides eluted with water from an ion-exchange column. The detection limits and linear determination ranges thus achieved make this reaction a valid alternative to the determination of carbohydrates.
Journal of the American Chemical Society, Apr 1, 2003
A novel series of terthiophenes bearing electron-donor and electron-acceptor groups at the end R-... more A novel series of terthiophenes bearing electron-donor and electron-acceptor groups at the end R-positions has been prepared. The analysis of the UV-vis, infrared, and Raman spectra, performed with the aid of density functional theory calculations, shows that the asymmetrically substituted nitro compounds PhT3NO2 and BrT3NO2 behave as push-pull systems and present an intense photoinduced charge transfer in the visible spectrum. The symmetrically substituted dinitro compound NO2T3NO2 displays a highly delocalized structure with a low single-double bond length alternation and also displays a low-energy absorption band in the visible region. The novel nitroterthiophenes possess attractive electrochemical properties since they generate stable species both upon oxidation and reduction. Oxidation mainly involves changes in the oligothiophene backbone and leads to the formation of stable cations even for NO2T3NO2. Reduction is mainly nitro-centered but also affects the conjugated structure. Radical anions and dianions are formed for PhT 3NO2 and BrT3NO2. Dianions, not radical anions, and trianions are obtained for NO2T3-NO2. Nitro-functionalized terthiophenes are shown to be very promising as electroactive molecular materials since they behave as push-pull systems, present a very intense photoinduced charge transfer in the visible region, and could act as both n-and p-channel conductors in organic electronic transistors.
Chemistry a European Journal, Oct 1, 2009
The Journal of Chemical Physics, 1994
Ab initio molecular orbital theory is employed to calculate the gas-phase barrier to internal rot... more Ab initio molecular orbital theory is employed to calculate the gas-phase barrier to internal rotation in 2,2'-bithiophene. Ground state geometries are fully optimized at the restricted Hat-tree-Fock level of theory using the 3-21G* and 6-31G ** basis sets. Methylation in @positions modulates the geometry, the inter-ring twist angle and the conformational properties of thiophene dimers. These methyl substitution effects have been assessed by calculations on the 3,4' and 3,3'-dimethyl derivatives in a number of selected conformations. A meaningful picture of the molecular relaxation on rotation is attained by allowing for full geometry optimization at both levels of calculation.
The Journal of Physical Chemistry B, Dec 1, 2005
In this Article, we report on the synthesis and full characterization of three perfluorinated oli... more In this Article, we report on the synthesis and full characterization of three perfluorinated oligothiophenes, ranging in length from the trimer to the pentamer (PF-nT, with n ) 3, 4, or 5). The differential pulse voltammetry (DPV) analysis of the compounds showed that they can be both oxidized and reduced (i.e., they display a dual or amphoteric electrochemical behavior), with the reduction peaks positively shifted relative to those of the corresponding unsubstituted oligothiophenes. The electrochemically determined energy gaps are in agreement with those measured from the UV-vis-NIR absorption spectra in solution. The conjugational properties have been investigated by means of FT-Raman spectroscopy, both as pure solids and as dilute solutes in CH 2 Cl 2 , revealing that: (i) π-conjugation does not still reach saturation with chain length for the longest oligomer, and (ii) conformational distortions from a nearly coplanar arrangement of the successive thiophene units upon solution are not too large. DFT and TDDFT quantum chemical calculations have been performed, at the B3LYP/6-31G** level, to assess information about the optimized molecular structure, equilibrium atomic charges distribution, energies and topologies of the frontier molecular orbitals (MO) around the gap, vibrational normal modes associated with the most outstanding Raman scatterings, and vertical oneelectron excitations that give rise to the main optical absorptions.
Radical cations of a heptathienoacene a,b-substituted with four n-decyl side groups (D4T7C + ) fo... more Radical cations of a heptathienoacene a,b-substituted with four n-decyl side groups (D4T7C + ) form exceptionally stable p-dimer dications already at ambient temperature (Chem. Comm. 2011, 47, 12622). This extraordinary p-dimerization process is investigated here with a focus on the ultimate [D4T7C + ] 2 p-dimer dication and yet-unreported transitory species formed during and after the oxidation. To this end, we use a joint experimental and theoretical approach that combines cyclic voltammetry, in situ spectrochemistry and spectroelectrochemistry, EPR spectroscopy, and DFT calculations. The impact of temperature, thienoacene concentration, and the nature and concentration of counteranions on the p-dimerization process is also investigated in detail.
J Phys Chem a, 2005
A series of R,ω-bis(mesitylthio)oligothiophenes of various chain lengths and with different side ... more A series of R,ω-bis(mesitylthio)oligothiophenes of various chain lengths and with different side substitution patterns have been studied in their oxidized states by means of electron absorption and Raman spectroscopies in combination with theory in the framework of the density functional theory. Upon chemical oxidation, stable radical cations, dications, and even radical trications are generated. Longer chain lengths better stabilize higher oxidation states. The tetramer can be easily converted to the dication, and a trication can be obtained for the ethylenedioxy derivative. The R,ω-sulfur atoms are actively involved in the formation of the charged species and exert a favorable tuning of their electronic structure. Raman spectra provide experimental evidence of the attainment of quinoidal structures within the conjugated path, initially heteroaromatic, with different extension as a function of the p-doping level.
El 60% de la producción mundial de frijol (Phaseolus vulgaris L.) se obtiene en condiciones de dé... more El 60% de la producción mundial de frijol (Phaseolus vulgaris L.) se obtiene en condiciones de déficit hídrico, por lo que este factor es el que más contribuye en la reducción del rendimiento después de las enfermedades . Entre las respuestas fisiológicas de las plantas al estrés hídrico está la disminución de la conductancia estomática Pattanagul y Madore, 1999) que causa reducción de la transpiración y de la fotosíntesis Pattanagul y Madore, 1999). La fotosíntesis en estrés hídrico también declina debido a la reducción en la fijación de C total (Brevedan y Egli, 2003), al daño en la maquinaria biosintética requerida para la asimilación de C y para su conversión a productos metabólicamente utilizables (Pattanagual y Madore, 1999). El déficit hídrico provoca además pérdida de reservas de almidón y de azúcares no estructurales que soportan el crecimiento y desarrollo, por la disminución en la actividad de la enzima fotosintética galactinol sintasa (Pattanagul y Madore, 1999).
Theoretical Chemistry Accounts, 2011
This work presents an analysis of the evolution of the molecular, vibrational and optical propert... more This work presents an analysis of the evolution of the molecular, vibrational and optical properties of a family of functionalized pentacenes. The analysis is performed on the basis of DFT quantum-chemical calculations in combination with spectroscopic techniques (Raman and UV-Vis). Theoretical calculations show that the bond length C-C/C=C alternation along the peripheral oligoenic ribbons increases with electron-releasing dioxolane substituents and diminishes with electron-withdrawing chlorine atoms and cyano groups. The attachment of triisopropylsilylethynyl groups increases the complexity of the Raman spectra. The spectra present many intense features of similar intensities in the 1,200-1,600 cm -1 range which are described by a combination of C-C/C=C stretching vibrations and in-plane C-H deformations spreading over the whole pentacene backbone. The absorption spectra display absorption bands in three different energy regions of the UV-Vis electromagnetic range. The spectra are dominated by a strong absorption band measured in the 300-350 nm region, which undergoes a sizeable red-shift with the substitution pattern, and a low-intensity, three-peak band in the 500-700 nm region, which undergoes a blue-or a red-shift depending on the electronic nature of the substituents. TDDFT calculations enable a detailed description of the trends observed in the absorption spectra.
Opt Mater, 1999
We present the results of an FT-IR and FT-Raman vibrational spectroscopic study carried out on α,... more We present the results of an FT-IR and FT-Raman vibrational spectroscopic study carried out on α, α'-diethylquinquethiophene and α, α'-diethylsexithiophene upon doping with iodine vapours and nitrosyl salts. The wavenumbers and intensity dispersions observed for the doping induced Raman bands with the oxidation degree are utilized to elucidate the conjugational defect-type. The near-infrared Raman spectra indicate the existence of radical cations and dications as the major oxidized species in the I 2-doped and NO-doped oligomers, respectively.
J Phys Chem B, 2002
In this paper, we investigate the vibrational properties of a novel family of amorphous molecular... more In this paper, we investigate the vibrational properties of a novel family of amorphous molecular materials containing an end-capped oligothiophene backbone of variable length, R,R′-bis-{4-[bis(4-methylphenyl)amino]-phenyl}-oligothiophene, which function as color-tunable emitting materials for organic light-emitting diodes. The advantage of these amorphous oligothiophenes with respect to their crystalline parents is that the fluorescence quantum efficiencies as thin films are quite similar to those commonly found in solution. The thorough analysis of the infrared and Raman spectra of the neutral materials as solids has revealed the uselfulness and selectivity of Raman spectroscopy to determine the efficiency of the π conjugation. Density functional theory B3LYP/3-21G* calculations rendered largely distorted conformations of the 4-[bis(4methylphenyl)amino]phenyl groups with respect to the thiophene rings least-squares plane, in full accordance with the amorphous nature of the materials. The infrared and Raman spectra of the materials recorded at different temperatures between -170 and +160°C did not show any substantial change, thus indicating that the materials have a high thermal stability, which has significance for their use as active components in optoelectronic devices.
J Phys Chem B, 2003
The in situ electronic absorption and Fourier transform Raman scattering spectra recorded during ... more The in situ electronic absorption and Fourier transform Raman scattering spectra recorded during the electrochemical oxidation of two R,R′-end-capped 4-[bis(4-methylphenyl)amino]phenyl oligothiophenes with three and four thiophene rings are reported. We have characterized a radical cation and a dication species in the trimer and up to a radical trication in the tetramer. The electronic and the Raman spectra have been interpreted and assigned with the final goal of obtaining structural information about the contribution of the bis(4-methylphenyl)amino groups, the innermost phenyl rings, and the central thienyl chain length to the stabilization of the electrochemically induced charged defects. The experimental data have been supported by theoretical calculations in the framework of the density functional theory. The charged defects can be viewed as models of hole carriers or photoexcitons in real devices.
In this work, we present a comparative study of the second order nonlinear optical properties of ... more In this work, we present a comparative study of the second order nonlinear optical properties of a series of chromophores containing a fused terthiophene, namely dithienothiophene (DTT), as electron relay with either D-π-A or D-π-D substitution patterns. The effect of the acceptor/donor strength and the solvent polarity confirm the possibility of fine-tuning optical non-linearities in the asymmetric samples. The geometrical and electronic properties calculated in solution reveal that push-pull chromophores become highly polarized as the dielectric constant of the solvent increases. Theoretical NLO calculations furthermore reveal a moderate nonlinear optical activity for the symmetric samples.
Chemistry of Materials, Oct 20, 2008
Electrochemical oxidation of bis-terthienyl-B (B ) ethane, disulfide, diacetylene, acetylene, eth... more Electrochemical oxidation of bis-terthienyl-B (B ) ethane, disulfide, diacetylene, acetylene, ethylene) has been investigated. Monomers without and with 3,3′′-dialkylsubstitution are regularly coupled to polymers alternating sexithiophene and B moieties. The corresponding terthienyl homopolymers have also been produced for comparison. The polymers obtained are characterized by cyclic voltammetry, EQCM, UV-vis, and FTIR spectroscopy, in situ ESR and in situ conductivity. The conductivities of p-doped polymers with ethane or disulfide bridges fall in a narrow range (1-5 × 10 -2 S cm -1 ) and are practically the same as those of R,ω-dimethylsexithiophene (1 × 10 -2 S cm -1 ), suggesting that conduction proceeds without the help of the links via a direct redox hopping between sexithiophene blocks of adjacent polymer chains. In the cases of diacetylene and acetylene, conduction changes from redox to bipolarontype but only in the case of ethylene the conductivity jumps to high values (1-5 S cm -1 ) corresponding to those of the polymers without the bridging moiety B, i.e., with shortened thiophene rings. DFT calculations of the bridge energy levels account for this result. (1) Walzer, K.; Maennig, B.; Pfeiffer, M.; Leo, K. Chem. ReV. 2007, 107, 1233. (2) (a) Kline, R. J.; McGehee, M. D.; Kadnikova, E. N.; Liu, J.; Frechet, J. M. J. AdV. Mater. 2003, 15, 1519. (b) Ong, B. S.; Wu, Y.; Liu, P.; Gardner, S. J. Am. Chem. Soc. 2004, 126, 3378. (3) Li, G.; Shrotriya, V.; Huang, J.; Yao, Y.; Moriarty, T.; Emery, K.; Yang, Y. Nat. Mater. 2005, 864. (4) Harima, Y.; Kim, D.-H.; Tsutitori, Y.; Jiang, X.; Patil, R.; Ooyama, Y.; Ohshita, J.; Kunai, A. Chem. Phys. Lett. 2006, 420, 387. (5) Zotti, G.; Schiavon, G.; Berlin, A.; Pagani, G. AdV. Mater. 1993, 5, 551. (6) Zotti, G.; Zecchin, S.; Vercelli, B.; Berlin, A.; Grimoldi, S.; Pasini, M. C.; Raposo, M. M. M. Chem. Mater. 2005, 17, 6492. (7) Zotti, G.; Zecchin, S.; Vercelli, B.; Pasini, M.; Destri, S.; Bertini, F.;
Portugaliae Electrochimica Acta, 2010
Journal of Molecular Structure, 2000
This paper reports results of a theoretical study about the effect of ionization on the infrared ... more This paper reports results of a theoretical study about the effect of ionization on the infrared and Raman spectra of a,a Hbis(aminomethyl)quaterthiophene with the objective of obtaining a deeper insight into the geometry and spectral changes occurring upon doping of the oligothiophenes and polythiophene. For these purposes, we determine the structures, vibrational frequencies and infrared intensities of the neutral compound and of its radical cation and dication. Ab initio calculations, at the B3LYP/6-31G ءء and RHF/6-31G ءء levels of theory, are employed to assess the structural and spectral information for the neutral and charged states. ᭧
J Liq Chromatogr Relat Techno, 1993
A comprehensive study of the reaction between Purpald (4-amino-3- hydrazino-5-mercapto-l, 2, 4-tr... more A comprehensive study of the reaction between Purpald (4-amino-3- hydrazino-5-mercapto-l, 2, 4-triazole) and eight neutral monosaccharides in order to establish the optimal conditions (wavelength, oxygen supply, temperature, time, pH and concentration range) was carried out. The reaction was applied to the post-column detection in HPLC of monosaccharides eluted with water from an ion-exchange column. The detection limits and linear determination ranges thus achieved make this reaction a valid alternative to the determination of carbohydrates.
Journal of the American Chemical Society, Apr 1, 2003
A novel series of terthiophenes bearing electron-donor and electron-acceptor groups at the end R-... more A novel series of terthiophenes bearing electron-donor and electron-acceptor groups at the end R-positions has been prepared. The analysis of the UV-vis, infrared, and Raman spectra, performed with the aid of density functional theory calculations, shows that the asymmetrically substituted nitro compounds PhT3NO2 and BrT3NO2 behave as push-pull systems and present an intense photoinduced charge transfer in the visible spectrum. The symmetrically substituted dinitro compound NO2T3NO2 displays a highly delocalized structure with a low single-double bond length alternation and also displays a low-energy absorption band in the visible region. The novel nitroterthiophenes possess attractive electrochemical properties since they generate stable species both upon oxidation and reduction. Oxidation mainly involves changes in the oligothiophene backbone and leads to the formation of stable cations even for NO2T3NO2. Reduction is mainly nitro-centered but also affects the conjugated structure. Radical anions and dianions are formed for PhT 3NO2 and BrT3NO2. Dianions, not radical anions, and trianions are obtained for NO2T3-NO2. Nitro-functionalized terthiophenes are shown to be very promising as electroactive molecular materials since they behave as push-pull systems, present a very intense photoinduced charge transfer in the visible region, and could act as both n-and p-channel conductors in organic electronic transistors.
Chemistry a European Journal, Oct 1, 2009
The Journal of Chemical Physics, 1994
Ab initio molecular orbital theory is employed to calculate the gas-phase barrier to internal rot... more Ab initio molecular orbital theory is employed to calculate the gas-phase barrier to internal rotation in 2,2'-bithiophene. Ground state geometries are fully optimized at the restricted Hat-tree-Fock level of theory using the 3-21G* and 6-31G ** basis sets. Methylation in @positions modulates the geometry, the inter-ring twist angle and the conformational properties of thiophene dimers. These methyl substitution effects have been assessed by calculations on the 3,4' and 3,3'-dimethyl derivatives in a number of selected conformations. A meaningful picture of the molecular relaxation on rotation is attained by allowing for full geometry optimization at both levels of calculation.
The Journal of Physical Chemistry B, Dec 1, 2005
In this Article, we report on the synthesis and full characterization of three perfluorinated oli... more In this Article, we report on the synthesis and full characterization of three perfluorinated oligothiophenes, ranging in length from the trimer to the pentamer (PF-nT, with n ) 3, 4, or 5). The differential pulse voltammetry (DPV) analysis of the compounds showed that they can be both oxidized and reduced (i.e., they display a dual or amphoteric electrochemical behavior), with the reduction peaks positively shifted relative to those of the corresponding unsubstituted oligothiophenes. The electrochemically determined energy gaps are in agreement with those measured from the UV-vis-NIR absorption spectra in solution. The conjugational properties have been investigated by means of FT-Raman spectroscopy, both as pure solids and as dilute solutes in CH 2 Cl 2 , revealing that: (i) π-conjugation does not still reach saturation with chain length for the longest oligomer, and (ii) conformational distortions from a nearly coplanar arrangement of the successive thiophene units upon solution are not too large. DFT and TDDFT quantum chemical calculations have been performed, at the B3LYP/6-31G** level, to assess information about the optimized molecular structure, equilibrium atomic charges distribution, energies and topologies of the frontier molecular orbitals (MO) around the gap, vibrational normal modes associated with the most outstanding Raman scatterings, and vertical oneelectron excitations that give rise to the main optical absorptions.
Vib Spectrosc, 2002
The FT-infrared spectra of two sexithiophenes having their end a,a 0 -positions substituted by n-... more The FT-infrared spectra of two sexithiophenes having their end a,a 0 -positions substituted by n-hexyl or -thiohexyl groups, in neutral and doped states, are studied with the main aim of deriving information about the p-electrons delocalization and about the electronic structure of the charged defects created upon doping with iodine. The analysis of the experimental data is aided by Density Functional Theory calculations. The modifications in the electronic structure of the sexithiophene backbone induced by the n-thiohexyl encapsulation are discussed from the point of view of single molecule interactions in thiol-terminated p-conjugated oligomers bound to metallic or cluster electrodes. #