An Important Key to Design Molecules with Small Internal Reorganization Energy: Strong Nonbonding Character in Frontier Orbitals

For an electron to move between molecules (reactants), structural reorganizations of the reactants and their surrounding molecules are needed. The energy cost of the reorganizations, which is determined by structural and electronic features of molecules involved, contributes to the energy barrier of an electron transfer reaction. Finding the factors affecting the energy cost is of fundamental and technological importance. It is believed that extended π-conjugation and a rigid molecular framework are beneficial for minimizing the energy cost. We prove with phenalenyl and phthalocyanine derivatives that the extent of local nonbonding character in frontier molecular orbitals is in fact more crucial than extended π-conjugation; unprecedented small energy cost for reorganization has been found with the help of the nonbonding character. This finding provides a much better understanding of the literature data, as well as a new focus of the molecular design of cutting-edge organic electronics materials

Alkyl(quinolin-8-yl)phosphine Oxides as Hemilabile Preligands for Palladium-Catalyzed Reactions

Preligands of quinolyl-substituted secondary phosphine oxides (SPOs, <b>2a</b>–<b>d</b>) were prepared and characterized. The unique palladium complex <b>3</b>, having a distorted-square-pyramidal structure, was obtained from the reaction of 2 equiv of <b>2c</b> with Pd­(COD)­Cl₂ or [Pd­(μ₂-Cl)­(η³-allyl)]₂. In the crystal structure of <b>3</b>, an apical chloride ligand and a supramolecular tetradentate ligand composed of a deprotonated <b>2c</b>′ and a neutral <b>2c</b>′ were resolved (<b>2c</b>′: PA form of <b>2c</b>). Intriguingly, the gas-phase optimized geometry of <b>3</b> converged to a distorted-square-planar structure, which was predicted by density functional calculations. The solid-state distorted-square-pyramidal structure of <b>3</b> can only be explained with the consideration of environmental effects (i.e., the electrostatic interactions between the surrounding molecules). As also evidenced by ³¹P NMR experiments performed in different deuterated solvents, the crystal structure of <b>3</b> is retained in solution. In the crystal structure of <b>3</b>, a long Pd–Cl bond was analyzed by energy decomposition analysis, showing that the bond is dominated by electrostatic character. Furthermore, application of these SPOs using the Heck reaction shows good reactivity toward common aryl bromides. The hemilabile preligand <b>2c</b> also tautomerizes to the competent ligand <b>2c</b>′ for palladium-catalyzed three-component reactions

Angular-Shaped Naphthalene Bis(1,5-diamide-2,6-diylidene)­malononitrile for High-Performance, Air-Stable <i>N</i>‑Type Organic Field-Effect Transistors

The synthesis, characterization, and application of two angular-shaped naphthalene bis­(1,5-diamide-2,6-diylidene)­malono­nitriles (NBAMs) as high-performance air-stable <i>n</i>-type organic field effect transistor (OFET) materials are reported. NBAM derivatives exhibit deep lowest-unoccupied molecular orbital (LUMO) levels, suitable for air-stable <i>n</i>-type OFETs. The OFET device based on <b>NBAM-EH</b> fabricated by vapor deposition exhibits a maximum electron mobility of 0.63 cm² V^–1 s^–1 in air with an on/off current ratio (<i>I</i>_on/<i>I</i>_off) of 10⁵