EPITAXIAL-GROWTH AND MOLECULAR-ORIENTATION OF TETRAPHENYLPORPHYRIN THIN-FILM VACUUM-EVAPORATED ON KCL

5,10,15,20-Tetraphenylporphyrin (H2TPP; C44H30N4, M(r) = 614.75) films were vacuum-evaporated onto a KCl (001) surface. High-resolution electron microscopy and electron diffraction patterns indicated that the H2TPP crystal in the film is monoclinic with dimensions a = 1.20, b = 1.90, c = 1.47 nm, beta = 91-degrees and Z = 4. The rectangular crystallites grow epitaxially along four directions, the (101) plane of the crystal making parallel contact with the substrate surface and the b axis making an angle of +/- 18.5-degrees with the KCl [100] or [010] directions. A high-resolution electron micrograph of the film showed fine structure in a thin crystal. Lattice fringes are aligned parallel with a spacing of 0.95 nm, and short parallel bands with a spacing of 0.38 nm are arranged obliquely in the lattice fringe. The optical diffraction pattern of the fine structure showed a long-period structure with an interval of 1.91 nm for every five bands. It is suggested that the planar molecules of H2TPP orient themselves nearly perpendicular to the substrate surface.