Ananth Reddy - Academia.edu (original) (raw)
Papers by Ananth Reddy
D-p-A organic dyes with carbazole as donor for dye-sensitized solar cells
Synthetic Metals, 2011
We have synthesized and characterized donor-spacer-acceptor type molecules in which 1,3,4oxadiazo... more We have synthesized and characterized donor-spacer-acceptor type molecules in which 1,3,4oxadiazoles are-spacers, triphenylamines are the donors and cyanoacetic acid are the acceptors for use as sensitizers in dye-sensitized solar cells (DSSCs). Detailed absorption, emission, electrochemical, photoelectrochemical and computational studies have been carried out on five novel derivatives. The dyes have an absorption range of 377-388 nm, and an emission in the range of 494-540 nm. There is a large charge transfer from the donor side to the acceptor side on excitation. The propeller shape of the triphenylamine and the bulky substituents on it help in reducing the dye-aggregation on TiO 2 surface. The dyes exhibited good overall conversion efficiency (2.79-3.21%). Plane wave calculations indicate that the dye has a reasonably strong binding to the TiO 2 surface and the generated DOS picture shows an overlap of the molecular orbitals of the dye and the TiO 2 bands. We conclude that the dyes have a promising role as sensitizers in DSSC.
Chemical structure dependent electron transport in 9,10-bis(2-phenyl-1,3,4-oxadiazole) derivatives of anthracene
RSC Advances, 2014
ABSTRACT In this work, we present a detailed analysis on electron transport studies of 9,10-bis(2... more ABSTRACT In this work, we present a detailed analysis on electron transport studies of 9,10-bis(2-phenyl-1,3,4-oxadiazole) derivatives of anthracene (OXD-PH, OXD-PTOL and OXD-OTOL). The effect of methyl substitution at ortho (OXD-OTOL) and para position (OXD-PTOL) on the phenyl ring on the electron transport properties was studied and the results were compared with the anthracene derivative without any substitution at the phenyl ring. Electron transport was found to be highly dependent on the methyl substitution and electron mobilities in OXD-PTOL and OXD-OTOL were found to be lower than in OXD-PH. Mobilities were also found to be different for OXD-PTOL and OXD-OTOL, which indicates that the substitution at different places did not have a similar effect on charge transport properties. Thickness dependent trap states were observed for all three molecules with thickness dependent electron mobilities. Electron mobility was found to increase in all three molecules with the decrease in thickness, which favors their use for organic electronic devices and all three molecules had a better electron transport in comparison to Alq3. These results were explained by the DFT calculation which showed a dihedral structure. The dihedral angle was found to reduce in the anionic form of these molecules. Therefore, these molecules are likely to favor a proper stacking in the solid state form.
The Journal of Physical Chemistry A, 2006
Molecular level parameters are investigated computationally to understand the factors that are re... more Molecular level parameters are investigated computationally to understand the factors that are responsible for the higher efficiency in derivatives of 9,10-bis(1-naphthyl)anthracene (R-ADN), 9,10-bis(2-naphthyl)anthracene (-ADN), their tetramethyl derivatives (R,-TMADN) and the t-Bu derivative (-TBADN) as blue light emitting electroluminescent (EL) layers in organic light emitting diodes (OLEDs). DFT studies at the B3LYP/6-31G-(d,p) level have been carried out on the substituted anthracenes. The absorption spectra are simulated using time dependent DFT methods (TD-DFT) whereas the emission spectra are approximated by optimizing the excited state by HF/CI-Singles and then carrying out the vertical CI calculations by the TD-DFT method. The reorganization energy for estimating the hole and electron transport is calculated. The transfer integrals between parallely stacked molecules in the bulk state are estimated by calculating the electronic splitting. The substituted anthracenes are compared with unsubstituted anthracene and yet untested 9,10-dianthrylanthracene (TANTH). A larger and slower buildup of the electrons and holes in the EL layer, due to the higher reorganization energy and smaller electronic coupling between the adjacent molecules could lead to an increase in hole-electron recombination in the layer and thus increase the efficiency.
Synthesis of novel twisted carbazole–quinoxaline derivatives with 1,3,5-benzene core: bipolar molecules as hosts for phosphorescent OLEDs
Tetrahedron Letters, 2011
... 1 Synthesis of novel twisted carbazole-quinoxaline derivatives with 1,3,5-benzene core : Bipo... more ... 1 Synthesis of novel twisted carbazole-quinoxaline derivatives with 1,3,5-benzene core : Bipolar molecules as hosts for phosphorescent OLEDs M. Ananth Reddy ,ab Anup Thomas,a G. Mallesham,ab B ... References [1] (a) Baldo, MA; Thompson, ME; Forrest, SR Pure Appl. ...
Synthetic Metals, 2011
Two donor-acceptor (D-A) organic dyes with carbazole as donor, phenylethynyl, thienylethynyl as-s... more Two donor-acceptor (D-A) organic dyes with carbazole as donor, phenylethynyl, thienylethynyl as-spacers and cyanoacrylic acid as acceptor, have been synthesized and characterized. These dyes exhibit charge transfer character in the ground and excited states as supported by the UV-vis and fluorescence studies. They also show interesting electrochemical properties. DFT and TDDFT studies reveal that large intramolecular charge transfer takes place from the HOMO to LUMO, though the donor carbazole is twisted (∼51 •) with respect to the-conjugated spacer and acceptors with an idea of testing the dyes as sensitizers for DSSC. The DSSC devices were fabricated with these dyes by using redox electrolyte in a nonvolatile methoxypropionitrile solvent. The efficiency of the cells, short circuit current density, J sc , and open circuit photovoltage, V oc , and fill factor, FF, has been obtained for the two molecules. Calculations based on DFT plane wave method reveal the strong binding of the dyes on the surface of TiO 2 (1 0 1) surface. It is concluded that these dyes can play the role of sensitizers in DSSC.
Synthetic Metals, 2010
Charge transport in 5,5-(2,6-di-tert-butylanthracene-9,10-diyl)bis(2-p-tolyl-1,3,4-oxadiazole) is... more Charge transport in 5,5-(2,6-di-tert-butylanthracene-9,10-diyl)bis(2-p-tolyl-1,3,4-oxadiazole) is investigated as a function of temperature and organic layer thickness. The thickness dependence of the current indicates towards the trap charge limited conduction (TCLC) with a field and temperature dependent mobility. The density of trap states has been found to be dependent on sample thickness. As the thickness has increased from 80 nm to 120 nm, trap energy has correspondingly increased from 78 meV to 130 meV. TCLC model with Poole Frenkel type field dependent mobility has been fitted into the data and has been found in excellent agreement. Temperature dependency of zero field mobility (0) andˇhas been estimated from the model.
Synthetic Metals, 2011
With a general aim to make anthracene derivatives multifunctional (n-type emitter) and also study... more With a general aim to make anthracene derivatives multifunctional (n-type emitter) and also study their suitability as electron transport layers for organic light emitting diodes (OLED), we report the synthesis and characterization of five novel molecules in which the 9 and 10 positions of anthracene have been directly substituted by 2,5-diphenyl-1,3,4-oxadiazole groups. We have carried out detailed characterization of these molecules which include photophysical, electrochemical, thermal, electroluminescent and computational studies. The electron affinity is very high, around 3.7 eV, and the ionization potential is around 6.7-6.8 eV, which is relatively higher than the most commonly used electron transport electroluminescent layer Alq 3. The studies reveal that the new molecules being reported by us, in addition to the high thermal stability, are quite efficient in a two layer unoptimized nondoped device with the device structure ITO/␣-NPD/10a-11b/LiF/Al and have an emission in pure blue. They also show very high efficiency as electron transport layer in device structure ITO(120 nm)/␣-NPD(30 nm)/Ir(ppy) 3 doped CBP(35 nm)/BCP(6 nm)/10a(28 nm)/LiF(1 nm)/Al(150 nm). From these studies we conclude that these anthracene derivatives also have considerable potential as multifunctional layers and as electron transport layers in OLED.
Photochemical & Photobiological Sciences, 2014
Six novel anthracene-oxadiazole derivatives, 4a (2-(4-(anthracen-9-yl)phenyl)-5-p-tolyl-1,3,4-oxa... more Six novel anthracene-oxadiazole derivatives, 4a (2-(4-(anthracen-9-yl)phenyl)-5-p-tolyl-1,3,4-oxadiazole), 4b (2-(4-(anthracen-9-yl)phenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole), 4c (2-(4-(anthracen-9-yl)phenyl)-5-(4-methoxyphenyl)-1,3,4-oxadiazole), 8a (2-(4-(anthracen-9-yl)phenyl)-5-m-tolyl-1,3,4oxadiazole), 8b (2-(3-(anthracen-9-yl)phenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole) and 8c (2-(3-(anthracen-9-yl)phenyl)-5-(3,4,5-trimethoxyphenyl)-1,3,4-oxadiazole) have been synthesized and characterized for use as emitters in organic light emitting devices (OLEDs). They show good thermal stability (T d , 297-364°C) and glass transition temperatures (T g) in the range of 82-98°C, as seen from the thermo gravimetric analysis and differential scanning calorimetric studies. The solvatochromism phenomenon and electrochemical properties have been studied in detail using UV-Vis absorption, fluorescence spectroscopy and cyclic voltammetry. TD-DFT calculations have been carried out to understand the electrochemical and photophysical properties. The spatial structures of 4b and 8c are further confirmed by X-ray diffraction analysis. Un-optimized non-doped electroluminescent devices were fabricated using these anthracene derivatives as emitters with the following device configuration: ITO (120 nm)/α-NPD (30 nm)/4a-4c or 8a-8c (35 nm)/BCP (6 nm)/Alq 3 (28 nm)/LiF (1 nm)/Al (150 nm). Among all the six compounds, 8a displays the maximum brightness of 1728 cd m −2 and current efficiency 0.89 cd A −1. Furthermore, as an electron transporter, 8a exhibited superior performance (current efficiency is 11.7 cd A −1) than the device using standard Alq 3 (current efficiency is 8.69 cd A −1), demonstrating its high potential for employment in OLEDs. These results indicate that the new anthraceneoxadiazole derivatives could play an important role in the development of OLEDs. † This article is dedicated in memory of Professor Nicholas J. Turro. ‡ Electronic supplementary information (ESI) available. See
Journal of Materials Chemistry, 2009
D-p-A organic dyes with carbazole as donor for dye-sensitized solar cells
Synthetic Metals, 2011
We have synthesized and characterized donor-spacer-acceptor type molecules in which 1,3,4oxadiazo... more We have synthesized and characterized donor-spacer-acceptor type molecules in which 1,3,4oxadiazoles are-spacers, triphenylamines are the donors and cyanoacetic acid are the acceptors for use as sensitizers in dye-sensitized solar cells (DSSCs). Detailed absorption, emission, electrochemical, photoelectrochemical and computational studies have been carried out on five novel derivatives. The dyes have an absorption range of 377-388 nm, and an emission in the range of 494-540 nm. There is a large charge transfer from the donor side to the acceptor side on excitation. The propeller shape of the triphenylamine and the bulky substituents on it help in reducing the dye-aggregation on TiO 2 surface. The dyes exhibited good overall conversion efficiency (2.79-3.21%). Plane wave calculations indicate that the dye has a reasonably strong binding to the TiO 2 surface and the generated DOS picture shows an overlap of the molecular orbitals of the dye and the TiO 2 bands. We conclude that the dyes have a promising role as sensitizers in DSSC.
Chemical structure dependent electron transport in 9,10-bis(2-phenyl-1,3,4-oxadiazole) derivatives of anthracene
RSC Advances, 2014
ABSTRACT In this work, we present a detailed analysis on electron transport studies of 9,10-bis(2... more ABSTRACT In this work, we present a detailed analysis on electron transport studies of 9,10-bis(2-phenyl-1,3,4-oxadiazole) derivatives of anthracene (OXD-PH, OXD-PTOL and OXD-OTOL). The effect of methyl substitution at ortho (OXD-OTOL) and para position (OXD-PTOL) on the phenyl ring on the electron transport properties was studied and the results were compared with the anthracene derivative without any substitution at the phenyl ring. Electron transport was found to be highly dependent on the methyl substitution and electron mobilities in OXD-PTOL and OXD-OTOL were found to be lower than in OXD-PH. Mobilities were also found to be different for OXD-PTOL and OXD-OTOL, which indicates that the substitution at different places did not have a similar effect on charge transport properties. Thickness dependent trap states were observed for all three molecules with thickness dependent electron mobilities. Electron mobility was found to increase in all three molecules with the decrease in thickness, which favors their use for organic electronic devices and all three molecules had a better electron transport in comparison to Alq3. These results were explained by the DFT calculation which showed a dihedral structure. The dihedral angle was found to reduce in the anionic form of these molecules. Therefore, these molecules are likely to favor a proper stacking in the solid state form.
The Journal of Physical Chemistry A, 2006
Molecular level parameters are investigated computationally to understand the factors that are re... more Molecular level parameters are investigated computationally to understand the factors that are responsible for the higher efficiency in derivatives of 9,10-bis(1-naphthyl)anthracene (R-ADN), 9,10-bis(2-naphthyl)anthracene (-ADN), their tetramethyl derivatives (R,-TMADN) and the t-Bu derivative (-TBADN) as blue light emitting electroluminescent (EL) layers in organic light emitting diodes (OLEDs). DFT studies at the B3LYP/6-31G-(d,p) level have been carried out on the substituted anthracenes. The absorption spectra are simulated using time dependent DFT methods (TD-DFT) whereas the emission spectra are approximated by optimizing the excited state by HF/CI-Singles and then carrying out the vertical CI calculations by the TD-DFT method. The reorganization energy for estimating the hole and electron transport is calculated. The transfer integrals between parallely stacked molecules in the bulk state are estimated by calculating the electronic splitting. The substituted anthracenes are compared with unsubstituted anthracene and yet untested 9,10-dianthrylanthracene (TANTH). A larger and slower buildup of the electrons and holes in the EL layer, due to the higher reorganization energy and smaller electronic coupling between the adjacent molecules could lead to an increase in hole-electron recombination in the layer and thus increase the efficiency.
Synthesis of novel twisted carbazole–quinoxaline derivatives with 1,3,5-benzene core: bipolar molecules as hosts for phosphorescent OLEDs
Tetrahedron Letters, 2011
... 1 Synthesis of novel twisted carbazole-quinoxaline derivatives with 1,3,5-benzene core : Bipo... more ... 1 Synthesis of novel twisted carbazole-quinoxaline derivatives with 1,3,5-benzene core : Bipolar molecules as hosts for phosphorescent OLEDs M. Ananth Reddy ,ab Anup Thomas,a G. Mallesham,ab B ... References [1] (a) Baldo, MA; Thompson, ME; Forrest, SR Pure Appl. ...
Synthetic Metals, 2011
Two donor-acceptor (D-A) organic dyes with carbazole as donor, phenylethynyl, thienylethynyl as-s... more Two donor-acceptor (D-A) organic dyes with carbazole as donor, phenylethynyl, thienylethynyl as-spacers and cyanoacrylic acid as acceptor, have been synthesized and characterized. These dyes exhibit charge transfer character in the ground and excited states as supported by the UV-vis and fluorescence studies. They also show interesting electrochemical properties. DFT and TDDFT studies reveal that large intramolecular charge transfer takes place from the HOMO to LUMO, though the donor carbazole is twisted (∼51 •) with respect to the-conjugated spacer and acceptors with an idea of testing the dyes as sensitizers for DSSC. The DSSC devices were fabricated with these dyes by using redox electrolyte in a nonvolatile methoxypropionitrile solvent. The efficiency of the cells, short circuit current density, J sc , and open circuit photovoltage, V oc , and fill factor, FF, has been obtained for the two molecules. Calculations based on DFT plane wave method reveal the strong binding of the dyes on the surface of TiO 2 (1 0 1) surface. It is concluded that these dyes can play the role of sensitizers in DSSC.
Synthetic Metals, 2010
Charge transport in 5,5-(2,6-di-tert-butylanthracene-9,10-diyl)bis(2-p-tolyl-1,3,4-oxadiazole) is... more Charge transport in 5,5-(2,6-di-tert-butylanthracene-9,10-diyl)bis(2-p-tolyl-1,3,4-oxadiazole) is investigated as a function of temperature and organic layer thickness. The thickness dependence of the current indicates towards the trap charge limited conduction (TCLC) with a field and temperature dependent mobility. The density of trap states has been found to be dependent on sample thickness. As the thickness has increased from 80 nm to 120 nm, trap energy has correspondingly increased from 78 meV to 130 meV. TCLC model with Poole Frenkel type field dependent mobility has been fitted into the data and has been found in excellent agreement. Temperature dependency of zero field mobility (0) andˇhas been estimated from the model.
Synthetic Metals, 2011
With a general aim to make anthracene derivatives multifunctional (n-type emitter) and also study... more With a general aim to make anthracene derivatives multifunctional (n-type emitter) and also study their suitability as electron transport layers for organic light emitting diodes (OLED), we report the synthesis and characterization of five novel molecules in which the 9 and 10 positions of anthracene have been directly substituted by 2,5-diphenyl-1,3,4-oxadiazole groups. We have carried out detailed characterization of these molecules which include photophysical, electrochemical, thermal, electroluminescent and computational studies. The electron affinity is very high, around 3.7 eV, and the ionization potential is around 6.7-6.8 eV, which is relatively higher than the most commonly used electron transport electroluminescent layer Alq 3. The studies reveal that the new molecules being reported by us, in addition to the high thermal stability, are quite efficient in a two layer unoptimized nondoped device with the device structure ITO/␣-NPD/10a-11b/LiF/Al and have an emission in pure blue. They also show very high efficiency as electron transport layer in device structure ITO(120 nm)/␣-NPD(30 nm)/Ir(ppy) 3 doped CBP(35 nm)/BCP(6 nm)/10a(28 nm)/LiF(1 nm)/Al(150 nm). From these studies we conclude that these anthracene derivatives also have considerable potential as multifunctional layers and as electron transport layers in OLED.
Photochemical & Photobiological Sciences, 2014
Six novel anthracene-oxadiazole derivatives, 4a (2-(4-(anthracen-9-yl)phenyl)-5-p-tolyl-1,3,4-oxa... more Six novel anthracene-oxadiazole derivatives, 4a (2-(4-(anthracen-9-yl)phenyl)-5-p-tolyl-1,3,4-oxadiazole), 4b (2-(4-(anthracen-9-yl)phenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole), 4c (2-(4-(anthracen-9-yl)phenyl)-5-(4-methoxyphenyl)-1,3,4-oxadiazole), 8a (2-(4-(anthracen-9-yl)phenyl)-5-m-tolyl-1,3,4oxadiazole), 8b (2-(3-(anthracen-9-yl)phenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole) and 8c (2-(3-(anthracen-9-yl)phenyl)-5-(3,4,5-trimethoxyphenyl)-1,3,4-oxadiazole) have been synthesized and characterized for use as emitters in organic light emitting devices (OLEDs). They show good thermal stability (T d , 297-364°C) and glass transition temperatures (T g) in the range of 82-98°C, as seen from the thermo gravimetric analysis and differential scanning calorimetric studies. The solvatochromism phenomenon and electrochemical properties have been studied in detail using UV-Vis absorption, fluorescence spectroscopy and cyclic voltammetry. TD-DFT calculations have been carried out to understand the electrochemical and photophysical properties. The spatial structures of 4b and 8c are further confirmed by X-ray diffraction analysis. Un-optimized non-doped electroluminescent devices were fabricated using these anthracene derivatives as emitters with the following device configuration: ITO (120 nm)/α-NPD (30 nm)/4a-4c or 8a-8c (35 nm)/BCP (6 nm)/Alq 3 (28 nm)/LiF (1 nm)/Al (150 nm). Among all the six compounds, 8a displays the maximum brightness of 1728 cd m −2 and current efficiency 0.89 cd A −1. Furthermore, as an electron transporter, 8a exhibited superior performance (current efficiency is 11.7 cd A −1) than the device using standard Alq 3 (current efficiency is 8.69 cd A −1), demonstrating its high potential for employment in OLEDs. These results indicate that the new anthraceneoxadiazole derivatives could play an important role in the development of OLEDs. † This article is dedicated in memory of Professor Nicholas J. Turro. ‡ Electronic supplementary information (ESI) available. See
Journal of Materials Chemistry, 2009