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ABSTRACT: The electrospray ionization collisionally activated dissociation (CAD) mass spectra of protonated 2,4,6-tris(benzylamino)-1,3,5-triazine (1) and 2,4,6-tris(benzyloxy)-1,3,5-triazine (6) show abundant product ion of m/z 181 (C(14) H(13)(+)). The likely structure for C(14) H(13)(+) is α-[2-methylphenyl]benzyl cation, indicating that one of the benzyl groups must migrate to another prior to dissociation of the protonated molecule. The collision energy is high for the 'N' analog (1) but low for the 'O' analog (6) indicating that the fragmentation processes of 1 requires high energy. The other major fragmentations are [M + H-toluene](+) and [M + H-benzene](+) for compounds 1 and 6, respectively. The protonated 2,4,6-tris(4-methylbenzylamino)-1,3,5-triazine (4) exhibits competitive eliminations of p-xylene and 3,6-dimethylenecyclohexa-1,4-diene. Moreover, protonated 2,4,6-tris(1-phenylethylamino)-1,3,5-triazine (5) dissociates via three successive losses of styrene. Density functional theory (DFT) calculations indicate that an ion/neutral complex (INC) between benzyl cation and the rest of the molecule is unstable, but the protonated molecules of 1 and 6 rearrange to an intermediate by the migration of a benzyl group to the ring 'N'. Subsequent shift of a second benzyl group generates an INC for the protonated molecule of 1 and its product ions can be explained from this intermediate. The shift of a second benzyl group to the ring carbon of the first benzyl group followed by an H-shift from ring carbon to 'O' generates the key intermediate for the formation of the ion of m/z 181 from the protonated molecule of 6. The proposed mechanisms are supported by high resolution mass spectrometry data, deuterium-labeling and CAD experiments combined with DFT calculations.
Biological Mass Spectrometry 07/2012; 47(7):860-8. · 3.41 Impact Factor
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ABSTRACT: The adsorption of model croconate dyes on the stoichiometric TiO 2 anatase (101) surface has been studied by means of periodic density functional calculations to understand the adsorption of the diketo (-COCO-) groups. Past experimental and theoretical results have shown the strong binding ability of the acid group (-COOH) to the TiO 2 surface but here the theoretical studies predicts the binding strength of the diketo group to be also significant and comparable with that of the -COOH group. This may cause a competitive binding between the keto groups and the acid groups on the TiO 2 surface in the case of croconate dyes and cause a reduction in the efficiency of the DSSC.
Journal of Chemical Sciences 02/2012; 124:301-310. · 1.18 Impact Factor
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M Ananth Reddy,
G Mallesham,
Anup Thomas,
Kola Srinivas,
V Jayathirtha Rao, K Bhanuprakash,
L Giribabu,
Rakhi Grover,
Arunandan Kumar,
MN Kamalasanan,
Ritu Srivastava
Synthetic Metals 03/2011; · 1.83 Impact Factor
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M. Ananth Reddy,
G. Mallesham, Anup Thomas,
Kola Srinivas,
V. Jayathirtha Rao, K. Bhanuprakash,
L. Giribabu,
Rakhi Grover,
Arunandan Kumar, M. N. Kamalasanan,
Ritu Srivastava
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ABSTRACT: 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 3.7eV, and the ionization potential is around 6.7–6.8eV, which is relatively higher than the most commonly used electron transport electroluminescent layer Alq3. 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/α-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(120nm)/α-NPD(30nm)/Ir(ppy)3 doped CBP(35nm)/BCP(6nm)/10a(28nm)/LiF(1nm)/Al(150nm). From these studies we conclude that these anthracene derivatives also have considerable potential as multifunctional layers and as electron transport layers in OLED.
Lancet. 01/2011; 161(9):869-880.
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Synthetic Metals 04/2010; · 1.83 Impact Factor
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ABSTRACT: Four anthracene based sensitizers, 3-(anthracene-9-yl)-2-cyanoacrylic acid (M1), 2-cyano-3-(10-methoxyanthracene-9-yl)acrylic acid (M2), 2-(anthracene-9-ylmethylene) malonic acid (M3), and 2-((10-methoxyanthracene-9-yl)methylene)malonic acid (M4) were designed and synthesized to understand the binding modes of anchoring groups ( and ) on the nanocrystalline TiO2(101) surface and on the efficiency of dye-sensitized solar cells (DSSCs). All four sensitizers have been fully characterized using ATR-FTIR, UV−vis, and CV. These sensitizers were tested in DSSCs using 0.05 M I2, 0.5 M 1,2-dimethyl-3-n-propylimidazolium iodide (DMPI), and 0.5 M lithium iodide (LiI) in methoxypropionitrile (MPN) redox electrolyte. The sensitizers having a monocarboxylic acid group, i.e., M1 and M2, have shown marginally higher IPCE and efficiency than M3 and M4 having dicarboxylic acid groups. To have a detailed understanding of this behavior, the adsorption and binding energies to the TiO2 surface of these dyes have been investigated using computational techniques (periodic DFT). The studies show that the cyanoacrylic acid anchoring group has a stronger binding to the TiO2 surface compared to the malonic acid anchoring group.
11/2009;
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Journal of Materials Chemistry 08/2009; 19(34):6172. · 5.97 Impact Factor
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ABSTRACT: Role of the donor groups connected to the oxyallyl central moiety (suggested to be a powerful acceptor) has been emphasized in the literature for tuning the absorption maxima and obtaining large NLO activity in croconates and squaraine dyes which are oxyallyl derivatives. Here we have prepared a series of new croconate dye model molecules with aniline and substituted anilines as strong donors to the oxyallyl ring. Using experimental and theoretical techniques like UV−visible spectra, degenerate four wave mixing (DFWM), density functional theory, time-dependent density functional theory, and symmetry adopted cluster-configuration interaction (SAC-CI), we have characterized linear absorption, nonresonant third order optical nonlinearity, charge transfer, and excited states of these molecules. We find that these molecules have smaller singlet diradical character and the absorption is not in the near-infrared (NIR), as other reported croconates, but in the 440−480 nm range. There is a larger charge transfer (CT) from the side groups to the central ring in these croconates evident from SAC-CI calculations compared to CT in NIR croconates. This clearly supports the model that the NIR absorption in oxyallyl derivatives is correlated to the singlet diradical character and not to the donor capacity. The γ values determined by DFWM experiments show large nonresonant values of −2.4 to −5.3 × 10−32 esu, which is larger than that of similar squaraines suggesting that the larger oxyallyl ring size and diradical character in croconates play the major role and not the donor groups. We conclude that with a noncentrosymmetric structure, tunable absorption (visible-NIR), and larger γ values, these less studied croconate dyes are more interesting and will have a major role to play than the widely reported centrosymmetric squaraines as molecular materials.
The Journal of Physical Chemistry C 01/2008; 112:13272-13280. · 4.80 Impact Factor
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ABSTRACT: We have carried out DFT studies on the Au–Cu binary clusters of size n = 6 with a view of studying the electronic property variation with changing structure and composition in these alloys. The Au 6 , Cu 6 and the binary clusters (with the formula Au x Cu 6Àx , x = 1–5) minimize to triangular structures. Properties like the dipole moments show an interesting trend in these structures. With increasing Cu content these binary clusters prefer to minimize to a structure with a larger dipole moment and with increasing Au content the min-imized structures prefer Au at locations that yield a smaller dipole moment. Deforming the structures to W-shape shows a red shift of the absorption maxima compared to the planar structures. The 'cap' shape and the 'W'-shape structures are of higher energy.
Journal of Molecular Structure THEOCHEM 11/2007; Journal of Molecular Structure: THEOCHEM 803 (2007) 89–93(803):89-93. · 1.44 Impact Factor
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ABSTRACT: We apply many criteria to estimate the diradical character of the ground state singlets of several oxyallyl derivatives. This is carried out as the oxyallyl derivatives like squaraine and croconate dyes can be represented by both mesoionic and diradical formulas, the domination of which would characterize its lowest energy transition. One criterion applied is the singlet-triplet gap, which is known to be inversely proportional to the diradical character. Another criterion is the occupation number; this is determined for the symmetry broken state of the molecules in the unrestricted formalism, and the difference of occupation in the HOMO and LUMO is related to the diradical character. The diradical character of all of the croconates and few squaraines is estimated to be large. All of these have absorption above 750 nm and can be classified as near infrared (NIR) dyes, leading to the inference that NIR absorptions in these molecules are largely due to the dominance of the diradical character. To understand the reliability of the DFT methods for the absorption property predictions of these molecules, TD-DFT studies to calculate the vertical excitation energies have been carried out, using the B3LYP/ BLYP exchange correlation functionals and the LB94 asymptotic functional with and without the inclusion of solvent. The deviations, in both the squaraine series (average lower diradical character), are found to be systematic, and with the inclusion of the solvent in the calculation, the deviations decrease. The best least-squares fit with the experimentally observed values using B3LYP /6-311G(d, p) for the symmetric squaraines yields an R value of 0.92 and, for the unsymmetric squaraines, an R value of 0.936. With inclusion of the solvent, the R value is 0.96 for the symmetric squaraines and 0.961 for the unsymmetric squaraines, indicating that these DFT functionals with linear scaling may be used to study these systems. The croconate dyes, however, have larger deviation from the experimentally observed values in all of the functionals studied even after inclusion of the solvent effects. The deviations are also not systematic. The deviation with respect to the experiment in this case is attributed to the average larger diradical character in this series.
The Journal of Physical Chemistry A 06/2007; 111(17):3378-86. · 2.95 Impact Factor
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ABSTRACT: Bis(benzofuranonyl)methanolate (BM4i4i) dye and croconate dyes (derivatives of oxyallyl molecules) in general are known to have intense transitions in the near-infrared (NIR) region, indicating small transition energies and large transition dipole moments. These molecules have been reported in the literature to have very large resonant third-order nonlinear optical (NLO) susceptibilities and molecular hyperpolarizabilities (gamma). In this work we investigate using density functional theory (DFT)/ab initio/symmetry adapted cluster-configuration interaction (SAC-CI) techniques the oxyallyl substructure and attribute the NIR transition and the NLO activity to this substructure, which is common in all these molecules. Using valence bond (VB) theory, an analysis of a three-state model of this substructure is carried out. It is seen that the mixture of an intermediate diradical character and some zwitterionic character in the molecule and a large coupling between these two VB resonance forms is responsible for large gamma values. This can be used as a design principle for increasing NLO activity in oxyallyl derivatives.
The Journal of Physical Chemistry A 04/2007; 111(10):1943-52. · 2.95 Impact Factor
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ABSTRACT: Series of substituted-s-triazines (1-22) were synthesized and evaluated for their in vitro antibacterial activity against six representative Gram-positive and Gram-negative bacterial strains. Many compounds have displayed comparable antibacterial activity against Bacillus sphaericus and significantly active against other tested organisms with reference to streptomycin.
European Journal of Medicinal Chemistry 12/2006; 41(11):1240-6. · 3.35 Impact Factor
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ABSTRACT: In order to study the keto and enol forms of cyanuric acid derivatives in the solid state, we have synthesized bis(2,4-benzyloxy)-6-(5H)-one-1,3,5-triazine, 1. Computational investigations indicate that keto form is more stable than enol form in both gas phase and solution phase
by 9.69–11.18kcalmol−1 IR and crystallographic analysis shows that 1 exists in keto form in the solid state also. To obtain the enol form in the solid state, we adopted co-crystallization with
an organic base. The crystal structures of both keto/amine and the enol/imine forms (in a co-crystal) are reported.
Structural Chemistry 11/2006; 17(6):561-568. · 1.85 Impact Factor
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ABSTRACT: Natural resonance theory (NRT) and natural bond orbital (NBO) analysis have been carried out on a simple symmetrical and an unsymmetrical substituted squaraine with a view of understanding the structure of the latter type of squaraines. It is found that there are some fundamental differences in the structure and bonding between these two types of squaraines particularly in the resonance weights and delocalization energies. These differences are expected to reflect in the low energy transitions and charge transfer in these squaraines. To investigate this, the nature of the lowest energy transitions occurring on excitation in unsymmetrical squaraines has been studied using high-level symmetry adapted cluster-configuration interaction method (SAC/SAC-CI) and compared with reported experimental observations. In general the agreement with the experimental data is very good. The transition dipole moment always lies on the pi-backbone and is quite large in magnitude. The ground state dipole moment in some cases does not change in the excited state upon excitation while in some other cases there is a large reduction/enhancement in the magnitude indicative of some charge rearrangement in this direction. Inclusion of the solvent using the IEFPCM model, a slightly better agreement with the experiment is found in some cases. Studies are carried out with a different basis set and it is found that the change in basis set has very little effect on the transition energies. In the case of weak side donor groups attached to the central ring the larger charge transfer to the central acceptor ring in general takes place from the O- atoms of the squarylium moiety while in the case of strong donors the charge transfer from the O- atoms to the central rings drop down. We have not observed any correlation between the charge transfer in the excited state to the central ring from the side donor groups and the lowest energy excitation in the molecules. Reduction of the HOMO-LUMO gap (an indication of increase of the diradicaloid character) always leads to a bathochromic shift.
The Journal of Physical Chemistry A 11/2006; 110(41):11717-29. · 2.95 Impact Factor
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ABSTRACT: Black dye (BD), isomer 1 ([Ru(II)(H3-tctpy)(NCS)3](-1), where H3-tctpy = 4,4',4' '-tricarboxy-2,2':6,2' '-terpyridine) is known to be an excellent sensitizer for dye-sensitized solar cells and exhibits a very good near-IR photo response, compared to other ruthenium dyes. Because isothiocyanate is a linear ambidentate ligand, BD has three other linkage isomers, [Ru(H3-tctpy)(NCS)2(SCN)](-1), isomer 2 and 2', and [Ru(H3-tctpy))(SCN)3](-1), isomer 3. In this study, we have calculated the geometry of BD and its isomers by DFT. Further, we have analyzed the bonding in these isomers using NBO methods. TDDFT calculations combined with scalar relativistic zero-order regular approximations (SR-ZORA) have been carried out to simulate the absorption spectra. Calculations have been performed for the isomers both in vacuo and in solvent (ethanol). The inclusion of the solvent is found to be important to obtain spectra in good agreement with the experiment. The first absorption bands are dominated by the metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT).
Inorganic Chemistry 10/2006; 45(19):7600-11. · 4.60 Impact Factor
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ABSTRACT: Black dye (BD), isomer 1 ([RuII(H3-tctpy)(NCS)3]-1, where H3-tctpy = 4,4‘,4‘ ‘-tricarboxy-2,2‘:6,2‘ ‘-terpyridine) is known to be an excellent sensitizer for dye-sensitized solar cells and exhibits a very good near-IR photo response, compared to other ruthenium dyes. Because isothiocyanate is a linear ambidentate ligand, BD has three other linkage isomers, [Ru(H3-tctpy)(NCS)2(SCN)]-1, isomer 2 and 2‘, and [Ru(H3-tctpy))(SCN)3]-1, isomer 3. In this study, we have calculated the geometry of BD and its isomers by DFT. Further, we have analyzed the bonding in these isomers using NBO methods. TDDFT calculations combined with scalar relativistic zero-order regular approximations (SR-ZORA) have been carried out to simulate the absorption spectra. Calculations have been performed for the isomers both in vacuo and in solvent (ethanol). The inclusion of the solvent is found to be important to obtain spectra in good agreement with the experiment. The first absorption bands are dominated by the metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT).
08/2006;
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ABSTRACT: 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 (alpha-ADN), 9,10-bis(2-naphthyl)anthracene (beta-ADN), their tetramethyl derivatives (alpha,beta-TMADN) and the t-Bu derivative (beta-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.
The Journal of Physical Chemistry A 02/2006; 110(3):1152-62. · 2.95 Impact Factor
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ABSTRACT: Four derivatives of 2,4,6-tris(benzylamino)-1,3,5-triazine are synthesized and detailed computational and nonlinear optical investigations are carried out. Computations indicate near degenerate conformations (C 3 and C 1 symmetry) in all systems in the gas phase; the dipole moments are also of similar magnitude in all of them except molecule 4 [2,4,6-tris(4-fluorobenzylamino)-1,3,5-triazine]. HRS measurements of these molecules in solution reveal moderately large b values; structure–property relations are analyzed through computations. These molecules have one added advantage of nearly 100% optical transmission through the visible range, due to the nonconjugated structure. Molecule 4 crystallizes in a noncentrosymmetric structure by adopting the conformation with the lower dipole moment; it also shows optical SHG in the solid state.
Journal of Materials Chemistry 10/2005; · 5.97 Impact Factor
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ABSTRACT: Symmetric croconate (CR) and squarylium dyes (SQ) are well-known near-infrared (NIR) dyes and, in general, are considered to be donor-acceptor-donor type molecules. It is established in the literature that CR dyes absorb in a longer wavelength region than the corresponding SQ dyes. This has been attributed to the CR ring being a better acceptor than the SQ ring. Thus increasing the donor capacity should lead to a bathochromic shift in both SQ and CR. On the other hand, some experiments reported in the literature have revealed that increasing the conjugation in the donor part of the SQ molecule leads first to red shift, which upon a further increase of the conjugation changes to a blue shift. Hence, to understand the role of the central ring and the substitutions in the absorption of these dyes, we carried out high-level symmetry-adapted cluster-configuration interaction (SAC-CI) calculations of some substituted SQ and CR dyes and compare the absorption energy with the existing experimental data. We found that there is very good agreement. We also carried out SAC-CI calculations of some smaller model molecules, which contain the main oxyallyl substructure. We varied the geometry (angle) of the oxyallyl subgroup and the substitution in these model molecules to establish a correlation with the bathochromic shift. We found that the charge transfer is very small and does not play the key role in the red shift, but on the other hand, the perturbation of the HOMO-LUMO gap (HLG) from both the geometry and substitution seems to be responsible for this shift. We suggest as a design principle that increasing the donor capacity of the groups may not help in the red shift, but introducing groups which perturb the HLG and decrease it without changing the MO character should lead to a larger bathochromic shift.
The Journal of Physical Chemistry A 10/2005; 109(38):8604-16. · 2.95 Impact Factor
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ABSTRACT: Dissociative electron ionization (70eV) of selenophene (C4H4Se) generates m/z 106 ions of composition [H2, C2, 80Se]+• and m/z 105 ions of [H, C2, 80Se]+. From tandem mass spectrometric experiments, Density Functional Theory (DFT) and ab initio calculations, it is concluded that these ions have the structure of selenoketene H2CCSe+• (1a+• )and selenoketyl HCCSe+ (2a+) ions respectively. The calculations predict that selenoketene ion 1a+• is separated by high energy barriers from its isomers selenirene (He)+• 1b+•, ethyne selenol (HCCSeH)+• 1c+•, (CCHSeH)+• 1d+• and (CCSeH2)+• 1e+•. The selenoketyl ion 2a+ is separated by high barriers from its isomers (CCHSe)+ 2b+, and (CCSeH)+ 2c+. Neutralization-reionization mass spectra (NRMS) of these structurally characterized ions confirmed that the corresponding neutral analogues, selenoketene H2CCSe 1a and selenoketyl radical HCCSe 2a• are stable in the rarefied gas phase. The relative, dissociation, and isomerization energies for selenoketene and selenoketyl ions and neutrals studied at B3LYP/6–31G(d,p) and G2/G2(MP2) levels are used to support and interpret the experimental results. Copyright © 2005 John Wiley & Sons, Ltd.
Biological Mass Spectrometry 05/2005; 40(6):796 - 806. · 3.41 Impact Factor
