4‐Di­methyl­amino­pyridinium bromide

The crystal and molecular structure of 4‐di­methyl­amino­pyridinium bromide, C₇H₁₁N₂^+.Br^?, (I), is built up by hydrogen‐bonded dimers of crystallographic 222 symmetry and four short C—H...halogen contacts. It is remarkable that (I) and 4‐di­methyl­amino­pyridinium chloride are not isostructural.     

2H‐Tetrakis(3,5‐di‐tert‐butyl)phenylporphyrin on a Cu(110) Surface: Room‐Temperature Self‐Metalation and Surface‐Reconstruction‐Facilitated Self‐Assembly

The adsorption behavior of 2H‐tetrakis(3,5‐di‐tert‐butyl)phenylporphyrin (2HTTBPP) on Cu(110) and Cu(110)–(2×1)O surfaces have been investigated by using variable‐temperature scanning tunneling microscopy (STM) under ultrahigh vacuum conditions. On the bare Cu(110) surface, individual 2HTTBPP molecules are observed. These molecules are immobilized on the surface with a particular orientation with respect to the crystallographic directions of the Cu(110) surface and do not form supramolecular aggregates up to full monolayer coverage. In contrast, a chiral supramolecular structure is formed on the Cu(110)–(2×1)O surface, which is stabilized by van der Waals interactions between the tert‐butyl groups of neighboring molecules. These findings are explained by weakened molecule–substrate interactions on the Cu(110)–(2×1)O surface relative to the bare Cu(110) surface. By comparison with the corresponding results of Cu–tetrakis(3,5‐di‐tert‐butyl)phenylporphyrin (CuTTBPP) on Cu(110) and Cu(110)–(2×1)O surfaces, we find that the 2HTTBPP molecules can self‐metalate on both surfaces with copper atoms from the substrate at room temperature (RT). The possible origins of the self‐metalation reaction at RT are discussed. Finally, peculiar irreversible temperature‐dependent switching of the intramolecular conformations of the investigated molecules on the Cu(110) surface was observed and interpreted.     

Physics perspectives of heavy-ion collisions at very high energy

The structure of stretchable electronics is based on the buckling of a thin film on a compliant substrate. Under anisotropic biaxial prestrains, this structure may buckle into several patterns, including cylindrical, checkerboard, and undulating patterns. The displacement and energy of each pattern are deduced analytically. By comparing their minimum potential energies, the critical buckling condition of each pattern is determined. After secondary bifurcation, the checkerboard pattern occurs just above the critical prestrains, but the undulating pattern dominates other regions. The buckling amplitude and wavenumber of the undulating pattern are shown under biaxial prestrains. Even if the structure is under equi-biaxial prestrains, it may buckle into an asymmetric undulating pattern.