One‐Pot Synthesis of Contracted and Expanded Porphyrins with meso‐CF3 Groups

Corrole and sapphyrin with the smallest meso‐substituents reported so far were prepared in a one‐pot synthesis that relies on a non‐aldehydic precursor for introducing CF₃ groups. The substantial amounts of products obtained by this facile pathway allowed for the full characterization of 5,10,15‐tris(trifluoromethyl)corrole, the access to a variety of stable chelates thereof and investigations that disclose the unique structural and chemical properties induced by the CF₃ substituents. The novel 5,10,15,20‐tetra(trifluoromethyl)sapphyrin undergoes only single protonation, which according to its crystal structure is stabilized by favorable non‐bonding F/H interaction between the meso‐CF₃ and the inverted pyrrolic NH.     

Research and Development with Stock-Dependent Spillovers and Price Competition in a Duopoly

This paper investigates the research and development accumulation and pricing strategies of two firms competing for consumer demand in a dynamic framework. A firm’s research and development is production-cost-reducing and can benefit from part of the competitor’s research and development stock without payment. We consider decisions in a game characterized by Nash equilibrium. In this dynamic game, a player’s action depends on whether the competitor’s current research and development stock are observable. If the competitor’s current research and development stock are not observable or observable only after a certain time lag, a player’s action can be solely based on the information on the current period t (open-loop strategy). In the converse case, it can also include the information on the competitor’s reaction to a change in the current value of the state vector (closed-loop strategy), which allows for strategic interaction to take place throughout the game. Given the cumulative nature of research and development activities, a primary goal of this paper is to determine whether, regardless of the observability of the competitor’s current research and development stock, free research and development spillovers generate a lower level of scientific knowledge than research and development appropriability. A second objective of the paper is to determine how the observability of the rival’s current research and development stock affects a firm’s research and development and pricing decisions and payoffs under imperfect research and development appropriability.     

PHOTOCATALYSIS, PHOTOREDUCTION, PHOTOOXIDATION AND PHOTOREDOX HYDROGEN TRANSFER REACTIONS OF METALLOPORPHYRINS

Abstract— Hydrogen transfer from tertiary amines to nitroaromatics is photocatalysed by Sn^IV and Ge^IV complexes of tetraphenylporphyrin. There are two photochemical steps, one involving hydrogen transfer to the catalyst, and the second being a hydrogen donation from the intermediate formed. The photoredox properties of para-substituted tin tetraphenyl porphyrin dichlorides can be correlated with the one electron oxidation-reduction potentials of the porphyrins and of the reduced intermediates. The steady-state concentration of intermediate and rate of product formation depend also on the electron donor and acceptor properties of, respectively, the amine and nitro-compound. Fluorescence results indicate that in both photochemical steps excited singlet states of porphyrins are involved and there is evidence for exciplex formation with ground state amine. Acetic anhydride has a cocatalytic effect but does not influence the quenching of porphyrin fluorescence by amine or the quertchirjg of the fluorescence of the intermediate by nitrobenzene.     

Crumpling a thin sheet

Crumpled sheets have a surprisingly large resistance to further compression. We have studied the crumpling of thin sheets of Mylar under different loading conditions. When placed under a fixed compressive force, the size of a crumpled material decreases logarithmically in time for periods up to three weeks. We also find hysteretic behavior when measuring the compression as a function of applied force. By using a pretreating protocol, we control this hysteresis and find reproducible scaling behavior for the size of the crumpled material as a function of the applied force.     

Postponed two-pricing and ordering opportunity for selling a single season inventoried product

Postponement strategies are becoming increasingly important in light of a global trend in which products’ life-cycles are decreasing, such that even products that are not traditionally considered seasonal become “obsolete” within a short period of time (e.g., electronic devices, new cars). Our work addresses postponed-pricing and ordering decisions for a retailer who sells a newsvendor-type inventoried product, in a selling season that is divided into two sub-periods. The division of the selling season enables the retailer to on-line adjust her decisions when faced with a scenario (one that is highly prevalent in reality) in which potential demand changes (increases or decreases) following consumers’ experiences of the product in early stages of the selling season. We assume that the retailer has two opportunities for receiving shipments: prior to the first sub-period and prior to the second one. The retailer determines each order quantity (base-stock level) on the basis of the demand distribution for the corresponding sub-period. In each sub-period, after observing additional market signals, the retailer determines the price of the product for that sub-period. With the aid of a stochastic programming approach, we develop optimization problems and solution methods in order to obtain pricing and ordering decisions that maximize the expected profit of the retailer. We present an extensive numerical example that compares the suggested strategy to three alternative strategies, and conclude that price postponement and responsiveness to demand changes can each reduce leftovers and lost sales as well as substantially increase expected profit.     

Theoretical studies of molecular complexes: a probe into basis set and correlation effects

We investigate the effect of basis set size, correlation effects and interplanar separation on the theoretical electronic structure of stacking complexes of para- and meta-hydroxyaruline with formamidinium cation, constructed as analogs for the complexes of 5- and 6-hydroxytryptamine with imidazolium cation.     

Electron charge redistribution following electrophilic attack on heterocycles: nitrogen as a charge transducer

It is shown that an electrophilic attack on the ring nitrogen in pyrrole or tryptamine produces an electron charge redistribution that is qualitatively different from the redistribution caused by an attack on the oxygen in furan. The electrophilic attacks are represented theoretically as interactions with a positive point charge and calculated by an ab-initio LCAO-SCF method with gaussian basis sets. Results show that an attacked nitrogen responds to the perturbation by moving electronic charge to the adjacent carbons whereas oxygen retains most of the charge polarized by the interaction. The nitrogen also acts as a charge transducer in other systems that are structurally very different. As a consequence of the charge redistribution, the comparative susceptibility of various sites in the heterocyclic molecules to an electrophilic attack may also depend on the response of the molecule to a prior attack on the heteroatom. The results indicate the need for dynamical reactivity considerations which reflect the variability in the molecular response to an incipient attack and the possibility that enhanced reactivity can be induced at certain sites by this response.     

QUANTUM MECHANICAL ANALYSIS OF ELECTRONIC TRANSITIONS IN SOME CYANINE DYE PHOTOSENSITIZERS

Abstract— INDO and CNDO/2 calculations of some cyanine dye photosensitizers are reported. The redistribution of electron charge density following various electronic transitions is analyzed and found to be localized mainly in the conjugated chains. The charge redistribution is shown to be strongly influenced by presence of the counter ion, which also proves to be a main factor in determination of the ionization energy values and symmetry of the molecular orbitals. The results suggest an ionization process different from the one considered in previous approaches, because the electron is shown here to leave the negative ion, with the conjugated cation acting as a "photon trap". This situation is shown to provide a link between different models of optical sensitization. Results and assumptions from other methods, including the 'electron gas' models for the conjugated chain, are discussed in view of the counter-ion effect and the chain–localized transitions found here.