Department of Chemistry
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Item Meta Effect of Absorption Energy in Donor–Acceptor Substituted Benzenoids: A Computational Study of Its Dependence on Acceptor Strength, Solvent Polarity, and Conjugation Length(ACS, 2014-08) Pati, Avik K.The present work focuses on theoretical understanding of electronic absorption energies of N,N-dimethylaniline with different ortho-, meta-, and para-substituted acceptor groups. The meta isomers exhibit the lowest absorption energy compared to the ortho and para derivatives. This unusual behavior of absorption energies of the meta isomers is related to the “meta effect” well-known in organic photochemical reactions. The meta effect of absorption energy of the derivatives is found to depend on the strength of acceptors, solvent polarity, and conjugation length. The meta derivatives with strong acceptor groups generally exhibit the lowest absorption energy over the other isomers irrespective of solvent polarity. However, the meta isomers with weak acceptor groups exhibit the meta effect only in highly polar solvents. The trend of the lowest absorption energies of the meta isomers is observed to change if the acceptor group is bridged through π conjugation unit (n) with the core moiety. The normal pattern of absorption energy that is the para isomer is of lowest energy is observed to occur for the derivatives where the repeated conjugation units (n) are between 2 and 4. The normal pattern of absorption energy is continued to observe from n > 4 for all the derivatives.Item Photophysical Impact of Diacetylenic Conjugation on Classical Donor–Acceptor Electronic Energy Pair(ACS, 2018-12) Pati, Avik K.Organic fluorophores with extended π-conjugation are important for their widespread applications. The present work provides photophysical insights into a diacetylene bridged classical donor–acceptor electronic energy pair, naphthalene–pyrene, in comparison with its constituents’ molecular structures, naphthyl and pyrenyl acetylenes, as well as parent naphthalene and pyrene chromophores. The diacetylenic dye loses the individual spectral identities of the donor and acceptor fluorophores exhibiting a locally excited (LE) emission (∼411 nm) from the overall molecular entity with high fluorescence quantum yields (0.55–0.84) in nonaqueous media. In contrast to the parent pyrene, the hybrid derivative shows a strongly allowed S0 → S1 transition. In mixed-aqueous media, the dye forms aggregates displaying a new red-shifted absorption (∼425 nm) as well as emission (∼510 nm) band. Unlike the hybrid dye, the naphthyl and pyrenyl acetylenes do not form aggregates. In the aggregate state of the hybrid fluorophore, electronic energy transfer takes place from the naphthyl moiety to pyrenyl ring. The excited-state photophysical properties of the dye are exploited in vapor sensing in the solid state.Item Diphenylisobenzofuran Bound to Nanocrystalline Metal Oxides: Excimer Formation, Singlet Fission, Electron Injection, and Low Energy Sensitization(ACS, 2018-11-20) Banerjee, TanmayWe report the photophysical properties of the dicarboxylated diphenylisobenzofuran dye (1) bound to nanocrystalline metal oxide surfaces. With increased surface loading of 1, emission from the films is significantly quenched but with a small amount of excimer emission at maximum surface loadings. Long-lived triplets were observed by ns TA spectroscopy that are consistent with singlet fission occurring on mesoporous ZrO2. The evolution of these triplets, however, could not be convincingly resolved by our subnanosecond TA spectroscopy. Dye-sensitized devices composed of 1 on a TiO2|Al2O3 core–shell structure exhibited an unusual decrease, increase, and then decrease in Jsc with respect to the thickness of Al2O3. In these films the Al2O3 acts as a tunneling barrier to slow electron injection from the singlet excited state such that singlet fission, and electron injection from the triplet state becomes competitive. Proof-of-principle self-assembled bilayer films that exhibit efficient triplet energy transfer from a low energy absorbing dye to 1 is demonstrated as another step toward a SF-based DSSC that can circumvent the Shockley–Queisser limit.Item Analysis of Poly(amidoamine) Dendrimer Structure by UV–Vis Spectroscopy(ACS, 2011-06-29) Pande, SurojitWe report a UV–vis spectroscopic study of four different types of poly(amidoamine) dendrimers. The results indicate that the degree of protonation of the interior tertiary amines of these dendrimers correlates directly to an absorption band with λmax in the range of 280–285 nm. Specifically, at low pH, the tertiary amines are protonated and the 280–285 nm band is absent. However, at elevated pH, when these groups are deprotonated, this band appears. Similar results were obtained for a simple model compound. The dependence of the 280–285 nm band on the chemical state of the tertiary amines of the dendrimers was confirmed by complexing them with Pd2+ and Pt2+. In this case the band disappears, and it only reappears when the metal ions are decomplexed following reduction with BH4–. Finally, filtration experiments showed that the absorption band between 280−285 nm arises exclusively from intact, or nearly intact, dendrimers rather than low-molecular-weight fragments.Item Synthesis, Absorption, and Fluorescence Studies of Coumaryl-Labelled Amino Acids and Dipeptides Linked Via Triazole Ring(CSIRO, 2015-04-07) Sakhuja, Rajeev; Pant, Debi D.Fluorophores based on 4-triazolyl, 7-hydroxy-4-triazolylmethyl, 4-O-triazolylmethyl, and 7-O-triazolylmethyl coumaryl-tagged amino acids and dipeptides were synthesized by copper-catalyzed [3 + 2] cycloaddition reaction between azido- or alkynyl-functionalized coumarins with alkynyl- or azido-functionalized amino acid and dipeptides in good-to-excellent yields. Steady-state absorption and the fluorescence properties of the synthesized conjugates were studied. The chemical applicability of these amino acid and peptide-based fluorophores was successfully demonstrated by their linear elongation by further tagging them with appropriate C- or N-terminus amino acid.Item Estimation of ground and excited-state dipole moments of synthesized coumarin derivative, (S)-(1-((7-hydroxy-2-oxo-2H-chromen-4-yl)methyl)-1H-1,2,3-triazol-4-yl)methyl 2-(((9H-fluoren-9-yl)methoxy)cabonylamino)-3-phenylpropanoate from a solvatochromic shift and theoretical methods(Elsiever, 2015-09) Sakhuja, Rajeev; Pant, Debi D.The electronic absorption and fluorescence spectra of coumarin derivative, (S)-(1-((7-hydroxy-2-oxo-2H-chromen-4-yl)methyl)-1H-1,2,3-triazol-4-yl)methyl2-(((9H-fluoren-9-yl)methoxy)cabonylamino)-3-phenylpropanoate have been studied in solvents of different polarities, and the data were used to study the solvatochromic properties. The absorption maximum remains almost unchanged with the increase in solvent polarity, whereas a red shift in fluorescence emission maximum was observed. Synthesized compound (S)-(1-((7-hydroxy-2-oxo-2H-chromen-4-yl)methyl)-1H-1,2,3-triazol-4-yl)methyl2-(((9H-fluoren-9-yl)methoxy)cabonylamino)-3-phenylpropanoate was characterized by 1H and 13C NMR, and FT-IR spectral studies. The ground and excited state dipole moments of molecule were obtained from Bakshiev's and Bilot–Kawski's equations by means of solvatochromic shift method. High value of dipole moment is observed for excited state as compared to ground state value and this is attributed to more polar excited state of molecule. Also, fluorescence emission peak undergoes a bathochromic shift with increase in the polarity of the solvent, confirming π → π* transition. Numerical calculations are performed using B3LYP/6-31G(d) level of theory for the ground state using Gaussian 03. Studies in different solvents are also done using IEF-PCM method and UA0 radii. A comparative analysis between the values of dipole moment in gas phase and various solvents is also done for the ground state.Item Experimental and theoretical study: Determination of dipole moment of synthesized coumarin–triazole derivatives and application as turn off fluorescence sensor: High sensitivity for iron(III) ions(Elsiever, 2015-12) Sakhuja, Rajeev; Pant, Debi D.Electronic absorption and fluorescence spectra of two synthesized coumarin–triazole based probes (S)-(1-((7-hydroxy-2-oxo-2H-chromen-4-yl) methyl)-1H-1,2,3-triazol-4-yl)methyl 2-(tert-butoxycabonylamino)-3-phenylpropanoate and (S)-(1-((7-hydroxy-2-oxo-2H-chromen-4-yl)methyl)-1H-1,2,3-triazol-4-yl) methyl 2-(benzyloxycabonylamino)-3-phenylpropanoate have been recorded at room temperature in wide range of solvents of different polarities. Synthesized compounds were characterized by 1H and 13C NMR, and FT-IR spectral studies. The ground and excited state dipole moments of molecules were obtained from Bakshiev's and Bilot–Kawski's equations by means of solvatochromic shift method. A DFT based studies in different solvents are also performed using IEF-PCM method and UA0 radii. A comparative analysis between the values of dipole moment in gas phase and various solvents is also performed for the ground state. The potential sensor behaviors of these compounds to metal ions have also been examined by fluorescence spectroscopy and these compounds exhibited as fluorescence sensor for the determination of Fe3+ ions in solution. Effect of various metal ions on fluorescent behavior was also studied. Both the synthesized compounds act as selective and sensitive sensor for micromolar detection of Fe3+ ions. Binding stoichiometry of Fe3+ ion detection was also investigated. Conventional binding energy calculations are performed to determine the relative stability of Fe(III) complexes.Item Solvatochromic shift and estimation of dipole moment of synthesized coumarin derivative: Application as sensor for fluorogenic recognition of Fe3 + and Cu2 + ions in aqueous solution(Elsiever, 2016-10) Sakhuja, Rajeev; Pant, Debi D.(S)-4-((4-((3-amino-2-oxo-4-phenylbutoxy)methyl)-1H-1,2,3-triazol-1-yl)methyl)-7 hydroxy-2H-chromen-2-one hydrochloride was synthesized and characterized by detailed spectroscopic studies such as 1H, 13C NMR and HRMS. Excited state dipole moment of synthesized compound was obtained using different solvatochromic shift methods. High value of dipole moment is observed for excited state as compared to ground state value and this is attributed to more polar excited state of molecule. Also, fluorescence emission peak undergoes a bathochromic shift with increase in the polarity of the solvent, confirming π → π* transition. The potential sensor behavior of the compound to metal ions has also been examined. Chemosensor shows the sensitivity for Fe3 + and Cu2 + over other metal cations in aqueous solution. The detection limits of Fe3 + and Cu2 + were calculated to be 143 nM and 71.31 μM, respectively. The LC–mass analysis indicated that 1:1 complex was formed between Fe3 + (or) Cu2 + and compound. Binding energy values for the complexation of the compound with metal ions are theoretically computed at M06/6–31 + G(d,p) level. The DFT based binding energy values show good correlation with the experimental observations.Item NEXT Evolution of Hierarchical Hexagonal Stacked Plates of CuS from Liquid−Liquid Interface and its Photocatalytic Application for Oxidative Degradation of Different Dyes under Indoor Lighting(ACS, 2010) Basu, MrinmoyeeBlue solution of copper(II) acetylacetonate complex, [Cu(acac)2] in dichloromethane (DCM) and an aqueous alkaline solution of thioacetamide (TAA) constitute a biphasic system. The system in a screw cap test tube under a modified hydrothermal (MHT) reaction condition produces a greenish black solid at the liquid−liquid interface. It has been characterized that the solid mass is an assembly of hexagonal copper sulfide (CuS) nanoplates representing a hierarchical structure. The as-synthesized CuS nanoplates are well characterized by several physical techniques. An ethanolic dispersion of CuS presents a high band gap energy (2.2 eV) which assists visible light photocatalytic mineralization of different dye molecules. Thus a cleanup measure of dye contaminated water body even under indoor light comes true.