Heterogeneous Catalytic Oxidations with In Situ-Generated Hypervalent Iodine-Based Porous Organic Polymers.

Porous organic polymers (POPs) are novel emergent materials for heterogeneous organocatalysis owing to their remarkable physicochemical stabilities. Through a bottom-up approach entailing diligent design of twisted biaryl building blocks with in-built o-iodobenzoic acid (IA) moieties, a series of POP precatalysts, p-OMeIA-POP, DiMeIA-POP, and m-OMeIA-POP, were synthesized by employing Friedel-Crafts alkylation. These IA-POP precatalysts can undergo in situ oxidation in the presence of Oxone® to generate hypervalent iodine(V) species (λ5-iodanes), in particular, modified o-iodoxybenzoic acid, popularly termed IBX, which mediates diverse oxidative transformations.

Synthesis of Acridone-Based Zn-Metal-Organic Framework (Zn-MOF) as a Photocatalyst: Application for Visible Light-Mediated Oxidation of Sulfides and Enaminones.

Acridone, a cyclic analogue of benzophenone that undergoes efficient intersystem crossing (ISC) to the triplet-excited state with near-unity quantum yield, was elaborated as a 3-connecting triacid linker, i.e., , to develop a photocatalytic metal-organic framework (MOF) for energy transfer applications; the triacid linker inherently features concave shapes, an attribute that is important for the construction of MOFs with significant porosity.

Synthesis and Excited-State Properties of Donor-Acceptor Azahelical Coumarins.

A set of three azahelical coumarins (s), namely, , , and , were rationally designed and synthesized, and their excited-state properties were comprehensively investigated. All three s are shown to display very high fluorosolvatochromic shifts as a result of significant intramolecular charge transfer in their excited states. The -quinoidal forms of the latter apparently contribute predominantly to large dipole moments in their excited states.

Visible Light-Induced Decomposition of Acyl Peroxides Using Isocyanides: Synthesis of Heteroarenes by Radical Cascade Cyclization.

Visible light-mediated facile synthesis of heteroarenes, namely, isoquinolines, benzothiazoles, and quinazolines, is demonstrated by employing isocyanides and inexpensive acyl peroxides. It is shown for the first time that singlet-excited isocyanides decompose acyl peroxides into aryl/alkyl radicals. The latter attack isocyanides, yielding imidoyl radicals that subsequently cyclize to afford heteroarene products.

Zwitterionic Luminescent 2D Metal-Organic Framework Nanosheets (LMONs): Selective Turn-On Fluorescence Sensing of Dihydrogen Phosphate.

While a plethora of organic linkers based on carboxylic acids have been utilized in the construction of MOFs, zwitterionic linkers that typify the attributes of naturally occurring amino acids have been exploited only scarcely to the best of our knowledge. Zwitterionic interior characteristics should be expected to impart unique properties to the resultant MOFs with a high potential to interact with guest species through electrostatic interactions. In our investigations with bis(-carboxyphenyl)imidazolylarenes as a novel class of linkers for the development of functional MOFs, we have found that bisimidazole-tetracarboxylic acid undergoes metal-assisted self-assembly with Zn(NO) to yield a layered MOF ().

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

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.

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

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.

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.

A zinc metal-organic framework, i.e., Zn-MOF (Zn-DBC), with ca.

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

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.

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

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.

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

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.

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

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.

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

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.

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

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.

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

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.

Influence of Cations on the Fluorescence Quenching of an Ionic, Sterically Congested Pyrenyl Moiety by Iodide in Water.

Quenching of the excited singlet states of a water-soluble, sterically congested tetraarylpyrene, 1,3,6,8-tetrakis(2,6-dimethyl-4-(α-carboxy)methoxyphenyl)pyrene (Py4C), by a series of iodide salts has been investigated by steady-state and time-resolved fluorescence measurements. Access to the pyrenyl group of Py4C is restricted sterically as a result of the four flanking (2,6-dimethylphenoxy)acetic acid groups and the energy costs associated with their rotation. Deprotonation of the carboxylic acid groups of Py4C permits examination of ion-ion electrostatic interactions on the rates of quenching by iodide salts in which different steric and electrostatic factors are introduced by varying the cationic portions.

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

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.

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.

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.

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

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.

New Insights into an Old Problem. Fluorescence Quenching of Sterically-Graded Pyrenes by Tertiary Aliphatic Amines.

Although the quenching of singlet-excited states of aromatic molecules by amines has been studied for several decades, important aspects of the mechanism(s) remain nebulous. To address some of the unknowns, steric, and electronic factors associated with the quenching of the singlet-excited states of three electronically related aromatic molecules, pyrene, 1,3,6,8-tetraphenylpyrene (TPPy), and 1,3,6,8-tetrakis(4-methoxy-2,6-dimethylphenyl)pyrene (PyOMe), by a wide range of tertiary aliphatic amines have been assessed quantitatively. Correlations among the steric and electronic properties of the amines and the pyrenes (e.

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

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.

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.

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.

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

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).

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

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.

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

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.