Conduction of molecular electronic devices: qualitative insights through atom-atom polarizabilities.

The atom-atom polarizability and the transmission probability at the Fermi level, as obtained through the source-and-sink-potential method for every possible configuration of contacts simultaneously, are compared for polycyclic aromatic compounds. This comparison leads to the conjecture that a positive atom-atom polarizability is a necessary condition for transmission to take place in alternant hydrocarbons without non-bonding orbitals and that the relative transmission probability for different configurations of the contacts can be predicted by analyzing the corresponding atom-atom polarizability. A theoretical link between the two considered properties is derived, leading to a mathematical explanation for the observed trends for transmission based on the atom-atom polarizability.

Spin-polarized conceptual density functional theory study of the regioselectivity in the [2+2] photocycloaddition of enones to substituted alkenes.

A study of the regioselectivity of the photochemical [2+2] cycloaddition of triplet enones with a series of ground-state electron-rich and electron-poor alkenes using density functional theory (DFT)-based reactivity descriptors is presented. Using the concepts of local softness combined with a local hard and soft acids and bases principle and a softness matching approach, the regioselectivity of this reaction can only be explained in the case of the interaction of the triplet enones with electron-rich alkenes. In the next part, the regioselectivity was assessed within the framework of conceptual spin-polarized conceptual DFT, considering response functions of the system's external potential v, number of electrons N, and spin number NS (with NS being the difference between the number of alpha and beta electrons in the spin-polarized system). Within this theory, the concepts of local spin philicity and donicity are introduced. Using the spin philicity concept, the regioselectivity can almost be completely interpreted as resulting from the interaction of the site on the alkene with the highest spin philicity (i.e., lowest destabilization upon increasing spin number) with the site showing the highest change of spin number on the enone expected to result in the largest stabilization of this species.