Infrared spectra and thermal decompositions of metal acetates and dicarboxylates

The infrared spectra of rare earth acetates have been studied to examine the metal-acetate bonding. The thermal decomposition of rare earth acetates as well as lead and copper acetates have been investigated in detail by employing thermogravimetric analysis and differential thermal analysis. Thermal decomposition of calcium dicarboxylates (malonate to sebacate) have been studied employing t.g.a. and d.t.a. Infrared spectra of the dicarboxylates have also been studied. Preliminary results on the products of decomposition of dicarboxylates have been reported

Nafion-TMS- and TMS-trifluoroacetate-induced rearrangements of cyclopropyl ketones - a procedure for the regioselective conversion of semibullvalenes to barrelenes

Trimethylsilyl trifluoroacetate (TMSTFA) and the polymer-supported sulfonate Nafion-TMS exhibit selective reaction modes in the opening of cyclopropyl ketones. The yields are generally high. Nafion-TMS rearranges the tricyclooctanones 1a and 1b to the bicyclooctenones 4a and 4b (while TMSTFA gives ring-opened adducts 6a,b) with high regioselectivity. Aro-semibullvalenes (8a, 14, 17a,b) are efficiently rearranged to arobarrelenes (7a, 13, 20a,b) by both reagents. The latter rearrangements have also been achieved in mixtures of trifluoroacetic acid and tetramethylsilane (TMS), where the acid combines with an unidentified impurity of commercial TMS to form a strong electrophilic agent. The electrophile-assisted rearrangement of the naphtho-semibullvalenes 14a+b resulted in conversion to the naphthobarrelenes 13a+b with the opposite regioselectivity to that observed for the thermal equilibration at 220°

Photoinduced electron-transfer processes in fullerene-based donor-acceptor systems

Photoinduced electron-transfer processes in fullerene-based donor-acceptor dyads (DBA) in homogeneous and cluster systems are summarized. Stabilization of charge has been achieved through the use of fullerene substituted-aniline/heteroaromatic dyads with tunable ionization potentials and also by using fullerene clusters. The rate constants for charge separation (kCS) and charge recombination (kCR) in fullerene substituted-aniline/heteroaromatic dyads show that forward electron transfer falls in the normal region of the Marcus curve and the back electron transfer in the inverted region of the Marcus parabola. Clustering of fullerene-based dyads assists in effective delocalization of the separated charge and thereby slows down the back electron transfer in these cases

Organic nanomaterials: morphological control for charge stabilization and charge transport

How grows it? Organic nanostructured materials have been projected as active components in optoelectronic devices. Recent efforts in manipulating the morphology of organic nanomaterials, particularly on their size and shape, are summarized in this Focus Review. Potential application of organic nanostructured materials in charge stabilization and transporting are also discussed. Chromophoric systems with proper recognition motifs can organize into well-defined arrays forming supramolecular assemblies and further into nanoscopic materials. The optical and electrical properties of organic nanomaterials depend upon the stacking modes of organic molecules and also on the kind of interaction between different chromophore units (such as H- and J-type aggregates). These types of aggregates can dramatically alter the opto-electronic properties of organic nanostructures. Hence efforts are currently directed towards manipulating the morphology of organic nanomaterials, particularly on their size and shape by adopting different techniques and these aspects are discussed. Recent studies have shown that such nanostructures are extremely important in the development of optoelectronic systems such as photovoltaic devices. This Focus Review also discusses the potential application of organic nanomaterials in charge stabilization and transport

Alkali metal-induced transformations of cis-1,2-dibenzoylalkenes: transformation of 11,12-dibenzoyl-9,10-dihydro-9,10-ethenoanthracene

The unexpected transformation of the title compound (1) into the hydroxycarboxylic acid (2) can be explained in terms of transformations of radical anions

Photochemistry of squaraine dyes. 1. Excited singlet, triplet, and redox states of bis[4-(dimethylamino)phenyl]squaraine and bis[4-(dimethylamino)-2-hydroxyphenyl]squaraine

Singlet and triplet excited states and the reduced and oxidized forms of two squaraine dyes, bis[4-(dimethylamino)- phenyllsquaraine (SQH) and bis[4-(dimethylamino)-2-hydroxyphenyl]squaraine (SQOH), have been investigated by picosecond and nanosecond laser flash photolysis. Both singlet and triplet excited states of SQH and SQOH have distinct and intense absorption maxima in the visible region. The lifetime of ISQOH (Ts= 3.0 ns) is considerably higher than %QH ( Ts= 1.5 ns) as the substituent OH group restricts rotational relaxation of the excited state. Both squaraine dyes exhibit poor intersystem crossing efficiency (Φisc <0.001). However, the excited triplets of SQH and SQOH can be generated by triplet-triplet sensitization. The oxidized forms of these dyes, which were generated by photolytic and pulse radiolytic methods, exhibit absorption maxima in the vicinity of the ground-state absorption. The cation radical of SQOH can also be generated by charge transfer between excited dye and Ti02 semiconductor colloids

Rearrangement of 1,3-dipolar cycloadducts derived from bis(phenylazo)stilbene: a DFT level mechanistic investigation

The 1,3-dipolar cycloaddition of bis(phenylazo)stilbene with activated ethene and ethyne derivatives and the subsequent rearrangement of the cycloadducts have been studied using model compounds at the B3LYP/6-31G(d) level of density functional theory (DFT). From the structural and electronic features, a five-membered zwitterionic ring system 9 (1,2,3-triazolium-1-imide system) formed from bis(phenylazo)ethylene is confirmed as the active 1,3-dipole species in the reaction. Formation of the 1,3-dipolar cycloadduct from the alkyne derivative is found to be 26.0 kcal/mol exergonic, and it requires an activation free energy of 19.4 kcal/mol. The 1,3-cycloadduct formed in the reaction undergoes a very facile migration of a nitrogen-bearing fragment, passing through a zwitterionic transition state. A small activation free energy of 8.2 kcal/mol is observed for this step of the reaction, and it is 19.6 kcal/mol exergonic. Further activation of the newly formed rearranged product is possible under elevated temperatures, again passing through a zwitterionic transition state and resulting in the formation of 2,5-dihydro-1,2,3-triazine derivatives. Such derivatives have been recently reported by Butler et al. (J. Org. Chem. 2006, 71, 5679). The charge separation in 9 and the zwitterionic transition states are stabilized through the p-system of the phenyl rings and the carbonyl groups. Similar structural, electronic, and mechanistic features are obtained for the reaction of 9 with the ethylenic dipolarophile acrylonitrile. Molecular electrostatic potential analyses of the 1,3-dipole and the zwitterionic transitions states are found to be very useful for characterizing their electron delocalization features. The solvation effects can enhance the feasibility of these reactions as they stabilize the zwitterionic transition states to a great extent

Thermal and photochemical transformations of hetero-1,3,5-hexatrienes into five-membered rings-possible pericyclic reactions

Heterosubstituted 1,3,5-hexatrienes undergo thermal and photochemical cyclizations, most of which can be viewed as pericyclic reactions. Numerous cyclizations of this type have been reported in the literature. This article presents a systematic account of such reactions, classified according to the number and nature of the heteroatoms

Steady-state and laser flash photolysis studies of 1-aziridinyl-1,2-dibenzoylalkenes

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