Substrate-Directed Growth of N-Heteropolycyclic Molecules on a Metal Surface

Abstract

N-Heteropolycyclic compounds are promising organic n-channel semiconductors for applications in field effect transistors. The adsorption behavior of these molecules on inorganic substrates is of great interest, since it affects the transport properties. Utilizing high-resolution electron energyloss spectroscopy (HREELS) and density functional theory (DFT), we determined the adsorption geometry of three different N-heteropolycyclic molecules as a function of coverage on Au(111). All three π-conjugated aromatic molecules adopt a planar geometry with respect to the substrate in both the monolayer (ML) and thin films (up to 10 ML). Contrary, in their crystal structure the molecules are tilted up to 82°between the molecular planes in neighboring stacks. Electronic HREELS and DFT calculations allowed the determination of the optical gaps of the molecules which are unaffected by the nitrogen substitution of the polycyclic aromatic hydrocarbons, while the frontier orbitals of the N-heteropolycyclic compounds are stabilized. The present study provides important aspects such as adsorption and electronic properties which are essential for designing organic-molecules-based electronic devices.

Influence of N-introduction in pentacene on the electronic structure and excited electronic states

“…15–28 High-resolution electron energy loss spectroscopy (HREELS) provides the required insight into both adsorption and electronic properties of molecular compounds at interfaces to (semi)conducting surfaces and within thin films. 11,29–39 Depending on the primary energy of the incident electrons molecular vibrations or electronic transitions can be excited, including optically forbidden transitions (singlet to triplet states) as already successfully demonstrated for some organic compounds 40–42 including also the N-heteropolycycle 6,13-diazapentacene (6,13-DAP). 12 While the adsorption and electronic properties of pentacene (PEN) and its derivatives adsorbed on various metallic substrates have been investigated in great detail (see for example ref.…”

Quinoxalinophenanthrophenazine Based Cruciforms

“…The electronic band gaps range from E g =2.8 eV for 12‐Ph t Bu 2 , E g =3.0 eV for 11‐Th , E g =3.2 eV for 11‐Ph t Bu and 11‐Ph t Bu 2 , and E g =3.6 eV for 11‐Ph i Pr . The calculated frontier orbital energies are in the same range as the energies of tert ‐butyl substituted and unsubstituted derivatives [37,41–42] …”

“…In QPPs the cross‐conjugation across the pyrene rings can best be described with additional Clar sextets, [13–14] by which an exceptionally high stability can be explained. In recent years, a great variety of QPP derivatives has been synthesized in order to modify optoelectronic properties, solid state packing and solubility [15–46] . To adjust optoelectronic properties of QPPs, various electron‐donating or ‐withdrawing substituents were introduced to the QPP backbone, but to the best of our knowledge exclusively on the peripheral rings fused with the pyrazine units, rather than at remaining positions of the pyrene core [18–19,22,28−29,47−49] .…”

Recent Advances in Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds

“…In another report, Tegeder et al investigated the adsorption geometry and electronic properties of C15.3a and its 2,11-di- tert- butyl analogue C15.4a as a function of coverage on Au(111). 303 Both molecules adopted a planar geometry with respect to the substrate in both a single monolayer and thin films (up to 10 monolayers thick). In contrast, in the crystal structures, a tilt of up to 82° was observed between molecular planes in neighboring stacks.…”