Accommodating unwelcome guests in inorganic layered hosts: inclusion of chloranil in a layered double hydroxide

The host-guest chemistry of most inorganic layered solids is limited to ion-exchange reactions. The guest species are either cations or anions to compensate for the charge deficit, either positive or negative, of the inorganic layers. Here, we outline a strategy to include neutral molecules like ortho- and para-chloranil, that are known to be good acceptors in donor-acceptor or charge-transfer complexes, within the galleries of a layered solid. We have succeeded in including neutral ortho- and para-chloranil molecules within the galleries of an Mg-Al layered double hydroxide (LDH) by using charge-transfer interactions with preintercalated p-aminobenzoate ions as the driving force. The p-aminobenzoate ions are introduced in the Mg-Al LDH via ion exchange. The intercalated LDH can adsorb ortho- and para-chloranil from chloroform solutions by forming charge-transfer complexes with the p-aminobenzoate anions present in the galleries. We use X-ray diffraction, spectroscopy, and molecular dynamics simulations to establish the nature of interactions and arrangement of the charge-transfer complex within the galleries of the layered double hydroxide.     

Baeyer–Villiger rearrangement of a substituted pyrrole by Oxone

Pyrroloxyls have been reported to exhibit very narrow EPR spectral lines, essential for in vivo imaging. En route to pyrroloxyls, we observed an unexpected Baeyer–Villiger rearrangement, leading to loss of aromaticity and formation of a 4,5-dihydro-1H-ketopyrrole.     

Amine attack on coordinated alkenes: an interconversion from anti-Markovnikoff to Markovnikoff products

A sequence of alkene complexes of platinum, PtCl(2)(PPh(3))(alkene) (alkene = ethylene, propene, 1-butene, cis-2-butene, 1-hexene, 1-octene, and 1-decene), has been prepared. These complexes are characterized by NMR spectroscopy, including assignment of each proton, and X-ray crystal structures of the 1-propene and 1-hexene complexes. Each complex was reacted with diethylamine. For the 1-hexene, 1-octene, and 1-decene complexes, the amine displaces the alkene. For the smaller alkenes, the diethylamine nucleophilically attacks the coordinated alkene. For propene and 1-butene, the low-temperature addition leads to the anti-Markovnikoff nucleophilic attack, which slowly converts at room temperature to the Markovnikoff product. The transformation from anti-Markovnikoff to Markovnikoff addition occurs without diethylamine dissociation.     

The tetrafluoro analogue of DMABN: anomalous fluorescence and mechanistic considerations

Absorption and emission properties of DMABN-F4, the tetrafluoro analogue of DMABN, have been investigated and compared with the parent compound. Unlike in DMABN, this new compound exhibits only a highly solvatochromic and strongly red-shifted charge transfer (CT) fluorescence and is characterized by the absence of an LE band even in nonpolar solvents. This evidences the faster formation of CT in the excited state as compared to DMABN. The low quantum yield values of DMABN-F4 suggest that the high rate of nonradiative decay takes place via internal conversion (IC) rather than intersystem crossing (ISC) as no phosphorescence is observed in rigid glass solvents at 77 K in contrast to DMABN. The emission transition moment and radiative rate constant values of DMABN-F4 in medium and highly polar solvents point to a forbidden emission in the excited state similar to that of DMABN. Electronic structure and twist potentials were also studied by quantum chemical calculations using ab initio and semiempirical methods. In contrast to DMABN, the dimethylamino group in DMABN-F4 is found to be twisted by around 30-50 degrees, but the photophysics are concluded to be analogous to DMABN with the addition of a very fast IC channel.     

Oligothiophene-Ring-Strapped Perylene Bisimides: Functionalizable Coaxial Donor–Acceptor Macrocycles

Aesthetic designs from nature enable new knowledge to be gained and, at the same time, inspire scientific models. In this context, multicomponent macrocycles embody the advantage of precisely positioning the structural units to achieve efficient communication between them. However, the construction of a functionalizable macrocycle for ultrafast charge separation and stabilization has not been attempted. Herein, we report the synthesis, crystal structure, and transient absorption of a new functionalizable macrocycle consisting of an oligothiophene-ring-strapped perylene bisimide. Transient absorption results point to a sequential improvement in charge separation and stabilization from the macrocycle to the corresponding linear dimer and 2D polymer due to the unique design. Our macrocycle design with a supportive spatial arrangement of the donor and acceptor units will inspire the development of more complex synthetic systems with exciting electron-transfer and charge-separation features.     

Markovian representation of a bilinear time series model and maximum likelihood estimation of the parameters

A bilinear time series (BLTS) model is expressed in the form of Akaike's Markovian representation in order to use the Kalman recursive estimation approach. It is shown that Akaike's Markovian representation of autoregressive moving average models of orderp and q (ARMA(p,q)) and that of the bilinear model are equivalent. This equivalence facilitates the maximum likelihood estimation of the parameters involved in the bilinear model, which otherwise is an unwieldy problem. The present approach can easily be extended to take into account missing observations     

Quantitative investigations of aggregate systems

Nanomaterials with disordered, ramified structure are increasingly being used for applications where low cost and enhanced performance are desired. A particular example is the use in printed electronics of inorganic conducting and semiconducting nanoparticles. The electrical, as well as other physical properties depend on the arrangement and connectivity of the particles in such aggregate systems. Quantification of aggregate structure and development of structure∕property relationships is difficult and progress in the application of these materials in electronics has mainly been empirical. In this paper, a scaling model is used to parameterize the structure of printed electronic layers. This model has chiefly been applied to polymers but surprisingly it shows applicability to these nanolayers. Disordered structures of silicon nanoparticles forming aggregates are investigated using small angle x-ray scattering coupled with the scaling model. It is expected that predictions using these structural parameters can be made for electrical properties. The approach may have wide use in understanding and designing nano-aggregates for electronic devices.