Publications by authors named "Jarugu Narasimha Moorthy"

59 Publications

Contrasting Photochromic and Acidochromic Behaviors of Pyridyl- and Pyrimidylethynylated Mono- and Bis-Benzopyrans.

ACS Omega 2021 Aug 2;6(32):21113-21124. Epub 2021 Aug 2.

Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India.

Investigation of photochromic and acidochromic behaviors of a set of pyridyl- and pyrimidylethynylated mono- and bis-benzopyrans reveals an intriguing influence of the -heteroaryl ring on spectrokinetic properties of the photogenerated -quinonoid colored reactive intermediates. While the absorption maxima of the pyridylethynylated bis-benzopyran and its photogenerated -quinonoid colored species undergo bathochromic shifts by ca. 40 and 22 nm, respectively, in the presence of an acid (e.g., trifluoroacetic acid (TFA)), the same remain unaffected for the analogous pyrimidylethynylated bis-benzopyran and its photogenerated -quinonoid colored species under similar conditions. Modification of the photochromic behavior of these benzopyrans and, hence, spectrokinetic properties of their photogenerated -quinonoid species in the presence of H is a consequence of relative proton affinities of -heteroaryl rings, i.e., pyridyl/pyrimidyl, and the resonance effects relayed through the ethynyl spacers in a push-pull π-delocalized-type skeleton; the mesomeric effects operate in a contrasting manner depending on the -heteroaryl ring in the absence and in the presence of an acid. These molecular systems offer a unique opportunity to modulate both photochromic and acidochromic properties of benzopyrans and their photogenerated colored -quinonoid intermediates by leveraging -heteroaromatic rings.
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http://dx.doi.org/10.1021/acsomega.1c02948DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8375091PMC
August 2021

Mechanoluminescence and aggregation-enhanced emission (AEE) of an In-MOF based on a 9,9'-diphenyl-9-fluorene tetraacid linker.

Nanoscale 2021 Jun;13(21):9668-9677

Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India.

A water-stable In-MOF, constructed based on a conformationally-flexible tetraacid linker, i.e., 2,7-bis(3,5-dicarboxyphenyl)-9,9'-diphenyl-9H-fluorene, i.e., H4DPF, is shown to exhibit a significantly enhanced solid-state fluorescence quantum yield (φf) of 23% in comparison with that of the linker (φfca. 4%) as a consequence of rigidification of the latter by metalation. Application of external stimulus in the form of grinding of the In-MOF leads to a drastic enhancement by 29%, φf from 23 to 52%. Solid-state absorption and emission spectra show that the absorption in the region of 368-550 nm gets diminished with a concomitant change in the emission maximum with a blue shift upon grinding. Fluorescence enhancement with grinding is correlated with a gradual reduction in the size of the particles, as established by SEM analysis. MOF particle aggregation has been invoked to account for the observed fluorescence enhancement in addition to a subtle conformational change in the structure of the linker upon grinding. Intriguingly, the ground MOF particles exhibit aggregation behaviour in the DMF-water solvent system with the emission further increasing up to 75% for the increase in the water fraction (fw) from 0 to 60%; hydrophobic aggregation of particles evidently leads to a change in the conformation of the linker and particle aggregation-enhanced emission (AEE). De-aggregation of particles ensues for fw = 70-90%, as reflected by a gradual decrease in the emission intensity. It is shown that the suspension of ground In-MOF particles in water permits sensing of metal ions, in particular Al3+ ions, by fluorescence quenching with detection at a sub-ppb level. The observed results comprise first demonstration of both mechanoluminescence and AEE of MOF particles.
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http://dx.doi.org/10.1039/d1nr00898fDOI Listing
June 2021

Temperature-Dependent Emission and Turn-Off Fluorescence Sensing of Hazardous "Quat" Herbicides in Water by a Zn-MOF Based on a Semi-Rigid Dibenzochrysene Tetraacetic Acid Linker.

Inorg Chem 2020 May 15;59(9):6202-6213. Epub 2020 Apr 15.

Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India.

A zinc metal-organic framework, i.e., Zn-MOF (Zn-DBC), with ca. 27% solvent-accessible void volume was synthesized from a rationally designed tetraacid based on sterically insulated dibenzo[,]chrysene core; the latter inherently features concave shapes. Due to rigidification of the fluorophore in the MOF, Zn-DBC exhibits a respectable fluorescence quantum yield of ca. 30% in the solid state. The fluorescent and water-stable Zn-DBC MOF was found to display intriguing temperature-dependent emission behavior with an activation barrier of 1.06 kcal/mol for radiationless deactivation from the singlet-excited state. It is shown that the Zn-MOF can be employed as an efficient sensory material for detection of hazardous "quat" dicationic herbicides in water by diffusion-limited "turn-off" fluorescence. Due to confinement of the cationic guest analytes within the pores of the MOF, the fluorescence quenching via excited-state charge transfer mechanism is shown to depend on the molecular size of the analyte in addition to the redox potentials. Remarkably, Zn-DBC permits sensing of DQ, a well-known toxic "quat" herbicide, with a detection limit as low as 2.8 ppm in water. The unique structural attributes of the Zn-MOF for highly efficient fluorescence sensing of toxic herbicides in water are thus exemplified for the first time.
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http://dx.doi.org/10.1021/acs.inorgchem.0c00307DOI Listing
May 2020

One-Pot Synthesis of 4-Carboalkoxy-Substituted Benzo[]coumarins from α- and β-Naphthols and Their Excited-State Properties.

ACS Omega 2020 Jan 27;5(1):207-218. Epub 2019 Dec 27.

Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India.

One-pot synthesis has been developed for 4-carboethoxybenzo[]coumarins starting from α-/β-naphthols. Accordingly, diverse 4-carboethoxybenzocoumarins can be synthesized in moderate-to-excellent (31-75%) isolated yields. The synthesis involves initial oxidation of naphthols to the intermediary 1,2-naphthoquinones with 2-iodoxybenzoic acid followed by a cascade of reactions, namely, Wittig olefination, Michael addition, β-elimination, and cyclization. Furthermore, we have comprehensively investigated the excited-state properties of differently substituted 4-carboalkoxybenzo[]coumarins. It is shown that they exhibit low to high fluorescence quantum yields (1-36%) and excited-state lifetimes (ca. 1-7 ns) depending on the substitution pattern and solvent employed.
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http://dx.doi.org/10.1021/acsomega.9b02489DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6963932PMC
January 2020

Coumarin-Annelated Regioisomeric Heptahelicenes: Influence of Helicity on Excited-State Properties and Chiroptical Properties.

J Org Chem 2019 Sep 22;84(17):10658-10668. Epub 2019 Aug 22.

Department of Chemistry , Indian Institute of Technology , Kanpur 208016 , India.

Two regioisomeric pairs of heptahelical mono- and biscoumarins that are differentiated by "" and "" disposition of the pyran-2-one moiety have been synthesized and investigated to understand the influence of helicity on excited-state and chiroptical properties. A slight variation in the helicities is found to manifest in contrasting excited-state properties of coumarin-annelated heptahelicenes; in addition to the intramolecular charge transfer, structural relaxation in the excited state is shown from theoretical calculations to cause decrease in the fluorescence quantum yield for a system with higher helicity. The optically pure enantiomers of heptahelical coumarins exhibit helicity-dependent chiroptical properties, namely, specific rotations, molar ellipticities, Cotton effects, and anisotropic dissymmetry factors. Theoretical calculations point to factors that are not readily explicable.
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http://dx.doi.org/10.1021/acs.joc.9b01126DOI Listing
September 2019

Redox-Reversible 2D Metal-Organic Framework Nanosheets (MONs) Based on the Hydroquinone/Quinone Couple.

Chemistry 2019 Mar 11;25(15):3835-3842. Epub 2019 Feb 11.

Department of Chemistry, Indian Institute of Technology, Kanpur, 208016, India.

2D metal-organic nanosheets (MONs), akin to graphene, have aroused immense contemporary interest. In our quest to develop functional 2D MONs based on organic linkers designed de novo, we reasoned that benzene-tetrabenzoic acid, which has been exploited tremendously in the construction of pillared metal-organic frameworks (MOFs), could be maneuvered readily to access redox-active MONs based on the benzoquinone/hydroquinone redox couple. Herein, we show that the self-assembly of 2,3,5,6-tetrakis(p-carboxyphenyl)hydroquinone H BTA with Zn(NO ) does lead to 2D metal-organic nanosheets that stack down the y axis, affording a layered Zn MOF. Although the crystals of the latter do not exhibit a discernible chemically induced redox switching behavior, the 2D MONs accessed by ultrasound-induced liquid-phase exfoliation (UILPE) lend themselves to a facile redox switching behavior. Treatment of a dispersion of the 2D MONs in methanol with phenyliodine(III) diacetate (PIDA) results in the oxidation of the hydroquinone core to benzoquinone. Remarkably, the latter can be reverted to the former by treatment with ascorbic acid as a reducing agent; indeed, the redox process can be made out by the naked eye. The results constitute the first example of chemically induced redox switching of 2D MONs. In view of emergent applications of 2D materials in general and MONs in particular, for example, improvement of the performance of membranes in separations by doping with MONs, the redox-switchable property may lead to the development of unique materials with heretofore unexplored potential.
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http://dx.doi.org/10.1002/chem.201805188DOI Listing
March 2019

Modulation of Excited-State Proton-Transfer Dynamics inside the Nanocavity of Microheterogeneous Systems: Microenvironment-Sensitive Förster Energy Transfer to Riboflavin.

Chemphyschem 2019 Mar 28;20(6):881-889. Epub 2019 Feb 28.

Department of Organic Chemistry, Indian Institute of Science, Bangalore, 560012, India.

The excited-state proton-transfer efficiency of a tetraarylpyrene derivative, 1,3,6,8-tetrakis(4-hydroxy-2,6-dimethylphenyl)pyrene (TDMPP), was investigated thoroughly in the presence of various surfactant assemblies, such as micelles and vesicles. The confined microheterogeneous environments can significantly retard the extent of the excited-state proton-transfer process, resulting in a distinguishable optical signal compared to that in the bulk medium. Physical characteristics of the surfactant assemblies, such as order, interfacial hydration, and surface charge, influence the proton transfer process and allow multiparametric sensing. A higher degree of interfacial hydration facilitates the proton-transfer process, while the positively charged head groups of the surfactants specifically stabilize the anionic form of the probe (TDMPP-O*). Furthermore, Forster energy transfer from the probe to riboflavin was studied in a phospholipid membrane, wherein the relative ratio of the neutral versus anionic forms (TDMPP-OH/TDMPP-O*) was found to influence the extent of energy transfer. Overall, we demonstrate how an ultrafast photophysical process, that is, the excited-state proton transfer, can be influenced by the microenvironment.
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http://dx.doi.org/10.1002/cphc.201801085DOI Listing
March 2019

Fluorescent 2D metal-organic framework nanosheets (MONs): design, synthesis and sensing of explosive nitroaromatic compounds (NACs).

Nanoscale 2018 Dec 26;10(47):22389-22399. Epub 2018 Nov 26.

Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India.

2D metal-organic framework nanosheets (MONs) lie at the heart of contemporary research on metal-organic materials. We have rationally designed and synthesized a fluorescent 6-connecting hexaacid linker HTPA based on the 1,3,5-triphenylbenzene core to access layered MOFs by metal-assisted self-assembly. Treatment of HTPA with In salt does indeed lead to a layered porous MOF, i.e.In-TPA. It is shown that the ultrasonication-induced liquid phase of exfoliation (UILPE) of the latter in a top-down fashion affords few-layer 2D metal-organic nanosheets (MONs). The delamination of 2D MONs in ethanol occurs with 'turn-on' fluorescence, which is otherwise suppressed in the bulk material. The exfoliated MONs in ethanol exhibit blue fluorescence with a respectable quantum yield of 0.15 and serve as efficient sensory materials for 'turn-off' fluorescence detection of explosive nitroaromatic compounds (NACs). While all nitroaromatics are found to quench the fluorescence of MONs, the most electron-deficient trinitrotoluene (TNT) exhibited the highest efficiency; at 2 mM concentration of TNT, the fluorescence of 2D MONs was found to be quenched with an efficiency of 80% (permitting the detection of TNT at ca. 11 ppm level), while that of the unmetallated linker, i.e.HTPA, was quenched with only 5% efficiency. The unique attributes of MONs, namely the rigidity of the linker upon metallation and porosity that facilitates guest confinement within the pores, for efficient sensing of nitroaromatics are thus demonstrated for the first time.
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http://dx.doi.org/10.1039/c8nr04992kDOI Listing
December 2018

Nitrogen-Free Bifunctional Bianthryl Leads to Stable White-Light Emission in Bilayer and Multilayer OLED Devices.

ACS Omega 2018 Feb 2;3(2):1416-1424. Epub 2018 Feb 2.

Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India.

White organic light-emitting diodes (WOLEDs) are at the center stage of OLED research today because of their advantages in replacing the high energy-consuming lighting technologies in vogue for a long time. New materials that emit white light in simple devices are much sought after. We have developed two novel electroluminescent materials, referred to as and , based on a twisted bianthryl core, which are brilliantly fluorescent, thermally highly stable with high and , and exhibit reversible redox property. Although inherently blue emissive, leads to white-light emission (CIE ≈ 0.28, 0.33) with a moderate power efficiency of 2.24 lm/W and a very high luminance of 15 600 cd/m in the fabricated multilayer nondoped OLED device. This device exhibited excellent color stability over a range of applied potential. Remarkably, similar white-light emission was captured even from a double-layer device, attesting to the innate hole-transporting ability of despite it being non-nitrogenous, that is, lacking any traditional hole-transporting di-/triarylamino group(s). Similar studies with led to inferior device performance results, thereby underscoring the importance of dibenzofuryl groups in . Experimental as well as theoretical studies suggest the possibility of emission from multiple species involving and its exciplex and electroplex in the devices. The serendipitously observed white-light emission from a double-layer device fabricated with an unconventional hole-transporting material (HTM) opens up new avenues to create new non-nitrogenous HTMs that may lead to more efficient white-light emission in simple double-layer devices.
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http://dx.doi.org/10.1021/acsomega.7b01712DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6641470PMC
February 2018

Anionic merocyanine dyes based on thiazol-2-hydrazides: reverse solvatochromism, preferential solvation and multiparametric approaches to spectral shifts.

Phys Chem Chem Phys 2018 Feb;20(6):4149-4159

Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India.

Anionic merocyanine colored dyes based on (4-nitro/cyanophenyl)-substituted thiazol-2-hydrazides (THAs), which are donor-π-acceptor type push-pull molecular systems and characterized with a strong intramolecular charge transfer (ICT) in the ground state, have been examined as reverse solvatochromic systems. THAs are shown to exhibit both positive and negative solvatochromism with a reversal of the latter occurring for solvents of E(30) value of ca. 45. The observed behavior is traceable to relative contributions of benzenoid and quinonoid resonance forms of the THAs and their stabilization by solvents to different degrees. Solvatochromic studies in binary mixtures of polar aprotic and protic solvents reveal that the latter are always preferred in the solvation microsphere of THAs. Multiparametric treatment of the E(dye) parameters by Catalán and Kamlet-Taft linear solvation energy relationships (LSERs) compellingly bears out the remarkable influence of hydrogen-bond donating (HBD) acidity, dipolarity and polarizability of the media on the spectral properties of the anionic dyes; hydrogen-bond accepting (HBA) basicity of the solvents is found to influence the least.
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http://dx.doi.org/10.1039/c7cp06766fDOI Listing
February 2018

Helicity-Dependent Regiodifferentiation in the Excited-State Quenching and Chiroptical Properties of Inward/Outward Helical Coumarins.

Chemistry 2017 Oct 21;23(59):14797-14805. Epub 2017 Sep 21.

Department of Chemistry, Indian Institute of Technology, Kanpur, 208016, India.

Influence of helicity on the excited-state as well as chiroptical properties of two sets of regiohelical coumarins that are differentiated by "inward" and "outward" disposition of the pyran-2-one ring has been investigated. A subtle difference in the helicities manifests in divergent excited-state properties and significant differences in the dipole moments. The latter permit heretofore unprecedented regiodifferentiation in the O-H⋅⋅⋅O hydrogen-bond assisted electron-transfer quenching by phenols. Furthermore, the enantiopure hexahelical coumarins exhibit strong Cotton effects and lend themselves to a very high differentiation in the specific rotations and anisotropic dissymmetry factors. The specific rotation observed for 6-in turns out being the highest of the values reported for all hexahelicenes reported so far.
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http://dx.doi.org/10.1002/chem.201701787DOI Listing
October 2017

Robust MOFs of "tsg" Topology Based on Trigonal Prismatic Organic and Metal Cluster SBUs: Single Crystal to Single Crystal Postsynthetic Metal Exchange and Selective CO Capture.

Chemistry 2017 May 8;23(30):7297-7305. Epub 2017 May 8.

Department of Chemistry, Indian Institute of Technology, Kanpur, 208016, India.

The self-assembly of a rigid and trigonal prismatic triptycene-hexaacid H THA with Co(NO ) or Mn(NO ) leads to isostructural metal-organic frameworks (MOFs) that are sustained by 6-connecting metal cluster [M (μ -O)(COO) ] secondary building units (SBUs). The Co- and Mn-MOFs, constructed from organic and metal-cluster building blocks that are both trigonal prismatic, correspond to the heretofore unknown "tsg" topology. Due to the rigidity and concave attributes of H THA, the networks in the Co- and Mn-MOFs are highly porous and undergo 3-fold interpenetration. The interpenetration imparts permanent microporosity and high thermal stability to the MOFs to permit postsynthetic metal exchange (PSME) and gas sorption. The PSME occurs in a single crystal to single crystal fashion when the crystals of Co- or Mn-MOFs are immersed in a solution of Cu(NO ) in MeOH/H O. Further, the isostructural robust MOFs exhibit significant gas sorption and remarkable selectivity for CO over N (ca. 100 fold) at ambient conditions. In fact, the postsynthetically-engineered Cu-THA exhibits better CO sorption than Co-THA and Mn-THA. A composite of effects that include pore dimensions (ca. 0.7 nm), unsaturated metal centers, and basic environments conferred by the quinoxaline nitrogen atoms appears to be responsible for the observed high CO capture and selectivity. The high symmetry and structural attributes of the organic linker seemingly dictate adoption of the trigonal-prismatic metal cluster SBU by the metal ions in the MOFs.
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http://dx.doi.org/10.1002/chem.201700139DOI Listing
May 2017

Remarkable influence of 'phane effect' on the excited-state properties of cofacially oriented coumarins.

Phys Chem Chem Phys 2017 Feb;19(6):4758-4767

Department of Chemistry, Indian Institute of Technology, Kanpur-208016, India.

A comprehensive investigation of the photophysics of a cofacially oriented bis-coumarin based on naphthalene, i.e., Cou-Nap, designed and synthesized to examine the influence of π-electronic communication between the two fluorophores, reveals exceptional excited-state properties. While the anticipated [2 + 2] photocycloaddition is not observed despite the fact that the two reactive coumarin units are at a distance of 3.8 Å, the fluorescence quantum yields and singlet lifetimes in different solvents are found to be remarkably higher when compared to those of the parent coumarin and a mono-coumarin model system, i.e., Cou-Dur. In addition to large solvent-induced Stokes shifts, Cou-Nap displays intriguing temperature-dependent emission in a nonpolar solvent such as cyclohexane. The observed photophysical properties are reconciled based on the so-called 'phane effect' that is operative in cyclophanes. In the latter, an effective π-π interaction between the aromatic rings modifies the attributes of the chromophore in such a manner that the observed properties cannot be associated with the individual aromatic rings. The temperature-dependent emission is proposed to arise as a consequence of thermally activated ISC from the singlet-excited state to one of the higher energy triplet states. The results constitute, for the first time, the demonstration of modification of the excited-state properties of a fluorophore in a non-cyclophane system by 'phane effect'.
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http://dx.doi.org/10.1039/c6cp07720jDOI Listing
February 2017

Fluoride-Triggered Ring-Opening of Photochromic Diarylpyrans into Merocyanine Dyes: Naked-Eye Sensing in Subppm Levels.

J Org Chem 2016 09 9;81(17):7741-50. Epub 2016 Aug 9.

Department of Chemistry, Indian Institute of Technology , Kanpur 208016, India.

The fluoride-mediated desilylation reaction has been exploited, for the first time, to trigger ring-opening of photochromic diarylbenzo-/naphthopyrans into highly colored anionic merocyanine dyes with high molar absorptivities to permit naked-eye sensing. The absorption spectral shifts, i.e., differences in the absorption maxima of colorless and colored forms, observed for a rationally designed set of silyloxy-substituted diarylpyrans subsequent to fluoride-induced ring opening are remarkably high (330-480 nm), and are unknown for any colorimetric probe. In particular, the disilyloxy-substituted diphenylnaphthopyran and its analog, in which the diphenyl groups are fused in the form of fluorene, allows "naked-eye" detection of fluoride in subppm levels (<1.0 ppm) in THF as well as in DMSO-H2O. The sensing is specific for fluoride among various other anions. This approach for colorimetric sensing of fluoride by ring-opening of the otherwise photochromic benzo-/naphthopyrans is heretofore unprecedented.
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http://dx.doi.org/10.1021/acs.joc.6b01361DOI Listing
September 2016

o-Iodoxybenzoic Acid-Initiated One-Pot Synthesis of 4-Arylthio-1,2-naphthoquinones, 4-Arylthio-1,2-diacetoxynaphthalenes, and 5-Arylthio-/5-Aminobenzo[a]phenazines.

J Org Chem 2016 08 28;81(15):6472-80. Epub 2016 Jul 28.

Department of Chemistry, Indian Institute of Technology , Kanpur 208016, India.

1,2-Naphthoquiones and their derivatives constitute an important category of compounds of relevance in pharmaceutical and material chemistry. It is shown that 1,2-naphthoquinones generated by o-iodoxybenzoic acid-mediated oxidation of 2-naphthols can be subjected to a cascade of reactions, namely oxidation, Michael addition, reduction, acetylation, and cyclocondensation, in the same pot to afford diverse 4-arylthio-1,2-naphthoquinones 2, 4-arylthio-1,2-diacetoxynaphthalenes 3, and 5-arylthio-/5-aminobenzo[a]phenazines 4 in very good isolated yields. The multistep single-pot synthesis occurs smoothly in DMF at rt.
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http://dx.doi.org/10.1021/acs.joc.6b01105DOI Listing
August 2016

Helicenes as All-in-One Organic Materials for Application in OLEDs: Synthesis and Diverse Applications of Carbo- and Aza[5]helical Diamines.

Chemistry 2016 Jun 31;22(27):9375-86. Epub 2016 May 31.

Department of Chemistry, Indian Institute of Technology, Kanpur, 208016, India), Fax: (+91) 512-2596806.

A set of eight helical diamines were designed and synthesized to demonstrate their relevance as all-in-one materials for multifarious applications in organic light-emitting diodes (OLEDs), that is, as hole-transporting materials (HTMs), EMs, bifunctional hole transporting + emissive materials, and host materials. Azahelical diamines function very well as HTMs. Indeed, with high Tg values (127-214 °C), they are superior alternatives to popular N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPB). All the helical diamines exhibit emissive properties when employed in nondoped as well as doped devices, the performance characteristics being superior in the latter. One of the carbohelical diamines (CHTPA) serves the dual function of hole transport as well as emission in simple double-layer devices; the efficiencies observed were better by quite some margin than those of other emissive helicenes reported. The twisting endows helical diamines with significantly high triplet energies such that they also function as host materials for red and green phosphors, that is, [Ir(btp)2 acac] (btp=2-(2'-benzothienyl)pyridine; acac=acetylacetonate) and [Ir(ppy)3 ] (ppy=2-phenylpyridine), respectively. The results of device fabrications demonstrate how helicity/ helical scaffold may be diligently exploited to create molecular systems for maneuvering diverse applications in OLEDs.
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http://dx.doi.org/10.1002/chem.201600668DOI Listing
June 2016

Remarkably selective and enantiodifferentiating sensing of histidine by a fluorescent homochiral Zn-MOF based on pyrene-tetralactic acid.

Chem Sci 2016 May 7;7(5):3085-3091. Epub 2016 Jan 7.

Department of Chemistry , Indian Institute of Technology , Kanpur-208016 , India . Email:

A highly luminescent and water-stable homochiral Zn-MOF, , , has been developed based on a pyrene-tetralactic acid, which inherently features concave shapes for guest inclusion, to explore sensing of amino acids by fluorescence quenching; the solid-state fluorescence quantum yield of the MOF was found to be 46%. The fluorescence of an aqueous suspension of was shown to be quenched specifically by histidine amongst all the other amino acids. Selective sensing of histidine is of prime importance due to its relevance in a variety of biological functions. The lack of quenching of fluorescence of by all the amino acids other than histidine has been rationalized based on the exchange of the cationic dimethylammonium species in the MOF crystals with histidine that is protonated in water; the latter is envisaged to quench the fluorescence charge transfer in the excited state. Furthermore, the homochiral crystals of were found to permit enantiodiscrimination in the quenching by the d- and l-forms such that the ratio of enantioselectivity, , /, is 1.8, as determined by Stern-Volmer quenching plots. The highly selective as well as enantiodifferentiating sensing of amino acids by MOFs is unprecedented for any sensor type.
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http://dx.doi.org/10.1039/c5sc03839aDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6005210PMC
May 2016

Mechanochemical solid-state synthesis of 2-aminothiazoles, quinoxalines and benzoylbenzofurans from ketones by one-pot sequential acid- and base-mediated reactions.

Org Biomol Chem 2016 Apr;14(17):4129-35

Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India.

α-Chloroketones - obtained by the atom-economical chlorination of ketones with trichloroisocyanuric acid (TCCA) in the presence of p-TSA under ball-milling conditions - were set up for a sequential base-mediated condensation reaction with thiourea/thiosemicarbazides, o-phenylenediamine and salicylaldehyde to afford 2-aminothiazoles, 2-hydrazinylthiazoles, quinoxalines and benzoylbenzofurans, respectively, in respectable yields. The viability of one-pot sequential acid- and base-mediated reactions in the solid state under ball-milling conditions is thus demonstrated.
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http://dx.doi.org/10.1039/c6ob00351fDOI Listing
April 2016

Hole-Transporting Materials Based on Twisted Bimesitylenes for Stable Perovskite Solar Cells with High Efficiency.

ChemSusChem 2016 Feb 15;9(3):274-9. Epub 2016 Jan 15.

Institute of Chemistry, Academia Sinica, Taipei, 115, Taiwan.

A new class of hole-transport materials (HTMs) based on the bimesitylene core designed for mesoporous perovskite solar cells is introduced. Devices fabricated using two of these derivatives yield higher open-circuit voltage values than the commonly used spiro-OMeTAD. Power conversion efficiency (PCE) values of up to 12.11% are obtained in perovskite-based devices using these new HTMs. The stability of the device made using the highest performing HTM (P1) is improved compared with spiro-OMeTAD as evidenced through long-term stability tests over 1000 h.
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http://dx.doi.org/10.1002/cssc.201501392DOI Listing
February 2016

Benzophenones as Generic Host Materials for Phosphorescent Organic Light-Emitting Diodes.

ACS Appl Mater Interfaces 2016 Jan 8;8(2):1527-35. Epub 2016 Jan 8.

Department of Chemistry, Indian Institute of Technology , Kanpur 208016, India.

Despite the fact that benzophenone has traditionally served as a prototype molecular system for establishing triplet state chemistry, materials based on molecular systems containing the benzophenone moiety as an integral part have not been exploited as generic host materials in phosphorescent organic light-emitting diodes (PhOLEDs). We have designed and synthesized three novel host materials, i.e., BP2-BP4, which contain benzophenone as the active triplet sensitizing molecular component. It is shown that their high band gap (3.91-3.93 eV) as well as triplet energies (2.95-2.97 eV) permit their applicability as universal host materials for blue, green, yellow, and red phosphors. While they serve reasonably well for all types of dopants, excellent performance characteristics observed for yellow and green devices are indeed the hallmark of benzophenone-based host materials. For example, maximum external quantum efficiencies of the order of 19.2% and 17.0% were obtained from the devices fabricated with yellow and green phosphors using BP2 as the host material. White light emission, albeit with rather poor efficiencies, has been demonstrated as a proof-of-concept by fabrication of co-doped and stacked devices with blue and yellow phosphors using BP2 as the host material.
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http://dx.doi.org/10.1021/acsami.5b11232DOI Listing
January 2016

A fluorescent paramagnetic Mn metal-organic framework based on semi-rigid pyrene tetra-carboxylic acid: sensing of solvent polarity and explosive nitroaromatics.

IUCrJ 2015 Sep 14;2(Pt 5):552-62. Epub 2015 Aug 14.

Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India.

An Mn metal-organic framework (Mn-MOF), Mn-L, based on a pyrene-tetraacid linker (H4 L), displays a respectable fluorescence quantum yield of 8.3% in spite of the presence of the paramagnetic metal ions, due presumably to fixation of the metal ions in geometries that do not allow complete energy/charge-transfer quenching. Remarkably, the porous Mn-L MOF with ∼25% solvent-accessible volume exhibits a heretofore unprecedented solvent-dependent fluorescence emission maximum, permitting its use as a probe of solvent polarity; the emission maxima in different solvents correlate excellently with Reichardt's solvent polarity parameter (E T (N)). Further, the applicability of Mn-L to the sensing of nitroaromatics via fluorescence quenching is demonstrated; the detection limit for TNT is shown to be 125 p.p.m. The results bring out the fact that MOFs based on paramagnetic metal ions can indeed find application when the quenching mechanisms are attenuated by certain geometries of the organic linkers of the MOF.
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http://dx.doi.org/10.1107/S2052252515012506DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4547823PMC
September 2015

Synthesis of o-Carboxyarylacrylic Acids by Room Temperature Oxidative Cleavage of Hydroxynaphthalenes and Higher Aromatics with Oxone.

J Org Chem 2015 Aug 4;80(16):8354-60. Epub 2015 Aug 4.

Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, INDIA.

A simple procedure for the synthesis of a variety of o-carboxyarylacrylic acids has been developed with Oxone (2KHSO5·KHSO4·K2SO4); the oxidation reaction involves the stirring of methoxy/hydroxy-substituted naphthalenes, phenanthrenes, anthracenes, etc. with Oxone in an acetonitrile-water mixture (1:1, v/v) at rt. Mechanistically, the reaction proceeds via initial oxidation of naphthalene to o-quinone, which undergoes cleavage to the corresponding o-carboxyarylacrylic acid. The higher aromatics are found to yield carboxymethyl lactones derived from the initially formed o-carboxyarylacrylic acids.
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http://dx.doi.org/10.1021/acs.joc.5b00292DOI Listing
August 2015

Carbon Dioxide Capture by a Metal-Organic Framework with Nitrogen-Rich Channels Based on Rationally Designed Triazole-Functionalized Tetraacid Organic Linker.

Inorg Chem 2015 Jul 6;54(14):6829-35. Epub 2015 Jul 6.

Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India.

A semirigid tetraacid linker H4L functionalized with 1,2,3-triazole was rationally designed and synthesized to access nitrogen-rich MOFs for selective adsorption of CO2. The cadmium MOF, that is, Cd-L, obtained by the reaction of H4L with Cd(NO3)2, is found to be a 3D porous framework structure that is robust to desolvation. Crystal structure analysis reveals channels that are decorated by the triazole moieties of L. Gas adsorption studies show that Cd-L MOF permits remarkable CO2 uptake to the extent of 99 and 1000 cc/g at 1 and 30 bar, respectively, at 0 °C. While literature survey reveals that MIL-112, constructed from a 1,2,3-triazole functionalized linker, exhibits no porosity to gas adsorption due to structural flexibility, the results with Cd-L MOF described herein emphasize how rigidification of the organic linker improves gas uptake properties of the resultant MOF.
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http://dx.doi.org/10.1021/acs.inorgchem.5b00722DOI Listing
July 2015

Amorphous host materials based on Tröger's base scaffold for application in phosphorescent organic light-emitting diodes.

ACS Appl Mater Interfaces 2015 Feb 27;7(5):3298-305. Epub 2015 Jan 27.

Department of Chemistry, Indian Institute of Technology , Kanpur 208016, India.

Tröger's bases (TBs) functionalized with carbazoles (TB-Czs) and phosphine oxides (TB-POs) were designed and synthesized as host materials for application in phosphorescent organic light-emitting diodes. The TB scaffold is shown to impart thermal stability with high Tg values (171-211 °C) as well as high triplet energies in the range of 2.9-3.0 eV. With a limited experimentation of the devices, it is shown that the TBs doped with a green phosphor, namely, Ir(ppy)3, permit impressive external efficiencies on the order of ca. 16% with a high brightness of ca. 3000-4000 cd/m2. Better device performance results are demonstrated by a small structural manipulation of the TB scaffold involving substitution of methyl groups in the core scaffold.
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http://dx.doi.org/10.1021/am508004nDOI Listing
February 2015

Single crystal-to-single crystal site-selective postsynthetic metal exchange in a Zn-MOF based on semi-rigid tricarboxylic acid and access to bimetallic MOFs.

Chemistry 2015 Feb 22;21(7):2759-65. Epub 2014 Dec 22.

Department of Chemistry, Indian Institute of Technology, Kanpur-208016 (India), Fax: (+91) 512-2597436.

The metal ions in a neutral Zn-MOF constructed from tritopic triacid H3 L with inherent concave features, rigid core, and peripheral flexibility are found to exist in two distinct SBUs, that is, 0D and 1D. This has allowed site-selective postsynthetic metal exchange (PSME) to be investigated and reactivities of the metal ions in two different environments in coordination polymers to be contrasted for the first time. Site-selective transmetalation of Zn ions in the discrete environment is shown to occur in a single crystal-to-single crystal (SCSC) fashion, with metal ions such as Fe(3+) , Ru(3+) , Cu(2+) , Co(2+) , etc., whereas those that are part of 1D SBU sustain structural integrity, leading to novel bimetallic MOFs, which are inaccessible by conventional approaches. To the best of our knowledge, site-selective postsynthetic exchange of an intraframework metal ion in a MOF that contains metal ions in discrete as well as polymeric SBUs is heretofore unprecedented.
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http://dx.doi.org/10.1002/chem.201406098DOI Listing
February 2015

Porous coordination polymers of diverse topologies based on a twisted tetrapyridylbiaryl: application as nucleophilic catalysts for acetylation of phenols.

Chemistry 2015 Jan 27;21(5):2241-9. Epub 2014 Nov 27.

Department of Chemistry, Indian Institute of Technology, Kanpur 208016 (India), Fax: (+91) 512-2597436.

Porous coordination polymers (CPs) with partially uncoordinated pyridyl rings based on rationally designed polypyridyl linkers are appealing from the point of view of their application as nucleophilic catalysts. A D2d -symmetric tetradentate organic linker L, that is, 2,2',6,6'-tetramethoxy-3,3',5,5'-tetrakis(4-pyridyl)biphenyl, was designed and synthesized for metal-assisted self-assembly aimed at porous CPs. Depending on the nature of the metal ion and the counter anion, the ligand L is found to function as a 3- or 4-connecting building block leading to porous CPs of diverse topologies. The reaction of L with Zn(NO3 )2 and Cd(NO3 )2 yields porous 2 D CPs of "fes" topology, in which the tetrapyridyl linker L serves as a 3-connecting unit with its free pyridyl rings well exposed into the pores. The functional utility of these porous CPs containing uncoordinated pyridyl rings is demonstrated by employing them as efficient heterogeneous nucleophilic catalysts for acetylation of a number of phenols with varying electronic properties and reactivities.
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http://dx.doi.org/10.1002/chem.201404552DOI Listing
January 2015

Oxidative cleavage of olefins by in situ-generated catalytic 3,4,5,6-tetramethyl-2-iodoxybenzoic acid/oxone.

J Org Chem 2014 Dec 17;79(23):11431-9. Epub 2014 Nov 17.

Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur 208016, India.

Oxidative cleavage of a variety of olefins to the corresponding ketones/carboxylic acids is shown to occur in a facile manner with 3,4,5,6-tetramethyl-2-iodobenzoic acid (TetMe-IA)/oxone. The simple methodology involves mere stirring of the olefin and catalytic amount (10 mol %) of TetMe-IA and oxone in acetonitrile-water mixture (1:1, v/v) at rt. The reaction mechanism involves initial dihydroxylation of the olefin with oxone, oxidative cleavage by the in situ-generated 3,4,5,6-tetramethyl-2-iodoxybenzoic acid (TetMe-IBX), and oxidation of the aldehyde functionality to the corresponding acid with oxone. Differences in the reactivities of electron-rich and electron-poor double bonds have been exploited to demonstrate chemoselective oxidative cleavage in substrates containing two double bonds.
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http://dx.doi.org/10.1021/jo502002wDOI Listing
December 2014

Excited-state properties of fluorenones: influence of substituents, solvent and macrocyclic encapsulation.

Phys Chem Chem Phys 2014 Aug;16(31):16436-45

Jacobs University Bremen, Campus Ring 1, D-28759 Bremen, Germany.

A comprehensive investigation of the photophysics of a broad set of fluorenones substituted with methoxy groups at different positions brings out the importance of the location of substituents on the fluorenone core in modulating fluorescence and radiationless deactivation by way of modification of the singlet-excited state energy and its character. While the substituents at para positions are found to affect neither the fluorescence quantum yield nor the lifetime, those at meta positions are found to significantly modify the latter. A cumulative effect is observed for the substituents in that the nonradiative decay (knr) becomes progressively dominant with an increasing number of meta-methoxy substituents. For example, the trimethoxy substitution in 2,4,7-trimethoxyfluorenone (8) is found to increase knr by ca. 30 fold relative to that of the parent fluorenone (1) in a polar aprotic solvent such as acetonitrile. The predominance of nonradiative decay (knr) is rationalized from stabilization of the singlet-excited state via partial charge transfer from meta-methoxy substituents to the carbonyl group. Accordingly, a nice correlation is observed for the nonradiative (knr) rate constants versus singlet-excitation energies derived from fluorescence emission maxima of all fluorenones in acetonitrile. The macrocyclic host cucurbit[7]uril (CB7) is found to not only enhance the fluorescence of the parent fluorenone (1) significantly, but also increase the singlet lifetime considerably. Based on the changes observed in the absorption spectra and the lifetimes determined, a 1:1 host–guest complex has been proposed with CB7. The fluorescence lifetime observed in the presence of CB7 suggests that the hydrophobic fluorenone (1) can be employed as a probe to report on a polar microenvironment shielded from hydrogen bonding interactions in a polar protic solvent.
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http://dx.doi.org/10.1039/c4cp01724bDOI Listing
August 2014

Helicity as a steric force: stabilization and helicity-dependent reversion of colored o-quinonoid intermediates of helical chromenes.

J Am Chem Soc 2013 May 23;135(18):6872-84. Epub 2013 Apr 23.

Department of Chemistry, Indian Institute of Technology, Kanpur, India.

Photolysis of regioisomeric helical chromenes 1 and 2 leads to colored reactive intermediates. While the latter generally decay quite rapidly, they are found to be longer lived in 1 and highly persistent in 2. The remarkable stability of the otherwise fleeting transient in 2 allowed isolation and structural characterization by X-ray crystallography. The structural analyses revealed that steric force inherent to the helical scaffold is the origin of stability as well as differentiation in the persistence of the intermediates of 1 and 2 (1Q and 2Q). The structure further shows that diphenylvinyl moiety in the TT isomer of 2Q gets splayed over the helical scaffold such that it is fraught with a huge steric strain to undergo required bond rotations to regenerate the precursor chromene. Otherwise, reversion of 2Q was found to occur at higher temperatures. Aazahelical chromenes 3 and 4 with varying magnitudes of helicity were designed in pursuit of o-quinonoid intermediates with graded activation barriers. Their photogenerated intermediates 3Q and 4Q were also isolated and structurally characterized. The activation barriers for thermal reversion of 2Q-4Q, as determined from Arrhenius and Eyring plots, are found to correlate nicely with the helical turn, which decisively determines the steric force. The exploitation of helicity is thus demonstrated to develop a novel set of photoresponsive helicenes 2-4 that lead to colored intermediates exhibiting graded stability. It is further shown that the photochromism of 2-4 in conjunction with response of 2Q-4Q to external stimuli (acid, heat, and visible radiation) permits development of molecular logic gates with INHIBIT function.
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http://dx.doi.org/10.1021/ja312027cDOI Listing
May 2013

Crystal engineering: lattice inclusion based on O-H···O hydrogen-bonded self-assembly and guest-induced structural mimicry.

J Org Chem 2012 Sep 4;77(18):7858-65. Epub 2012 Sep 4.

Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India.

Pyrene-tetraphenol TP2 constitutes a molecular system with inherent features for inclusion of two or more guest molecules that are complementary in terms of size and shape. Hydrogen-bonded self-assembly of TP2 in the solid state is shown to lead to voids within which the guest molecules are incorporated. A large aromatic expanse extant to the pyrene core in TP2 permits inclusion of two different types of guest species interchangeably. The robust association manifests in packing equivalence in all of the inclusion compounds of TP2 with the exception of the compound formed with pyridine and o-dichlorobenzene guests; in the latter, pyridine terminates the otherwise 3-dimensional hydrogen-bonded organization. The half-component of TP2, i.e., 4,6-bis(4-hydroxyphenyl)-m-xylene (BX), deduced by simple structural reduction, is shown to exhibit guest inclusion, but with considerably less guest accessible volume. The limited yet meaningful set of guests allows mimicry of the two expected patterns of molecular organization based on hydrogen bonding for both TP2 and BX in the solid state.
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http://dx.doi.org/10.1021/jo3010292DOI Listing
September 2012
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