Lock and Key Adsorption Chemistry: Preferential Absorption of an Isomer of Di-iodobenzene on Molecular Films of Quinonoid Zwitterions

Abstract

We have investigated the absorption and adsorption of three isomers of di-iodobenzene on molecular films of a zwitterionic p-benzoquinonemonoimine-type molecule which is characterized by a large intrinsic dipole of 10 D. Specifically, we compared the reversible adsorption and absorption of 1,2-di-iodobenzene, 1,3-di-iodobenzene, and 1,4-di-iodobenzene on molecular films of (6Z)-4-(butylamino)-6-(butyliminio)-3-oxocyclohexa-1,4-dien-1-olate C6H2(···NHR)2(···O)2 where R = n-C4H9. We provide unequivocal evidence that molecular adsorption and absorption of 1,3-di-iodobenzene are strongly favored at 150 K over that of the other isomers of di-iodobenzene.

Approaching an organic semimetal: Electron pockets at the Fermi level for a p‐benzoquinonemonoimine zwitterion

“…3a and 1.63 eV from DFT. Although the vertical energy gap is much larger than the DFT calculated band gap, this remains much smaller than for other similar zwitterions [20,21], and this is in better agreement than previously observed for any DFT calculation for a zwitterion of this class of molecules. It is more typical that the HOMO to LUMO shows far better agreement with the larger gap calculated through semiempirical modeling [20, 21].…”

“…Combined ultraviolet photoemission (UPS) and inverse photoemission (IPES) spectra were taken in a single ultrahigh vacuum chamber to study the placement of both occupied and unoccupied molecular orbitals of the zwitterions, as has been done elsewhere for other p -benzoquinonemonoimine zwitterion molecular films [20, 21]. The IPES were obtained by using variable kinetic energy incident energy electrons while detecting the emitted photons at fixed energy (9.7 eV) using a Geiger–Müller detector.…”

“…The IPES were obtained by using variable kinetic energy incident energy electrons while detecting the emitted photons at fixed energy (9.7 eV) using a Geiger–Müller detector. The IPES was limited by an instrumental line width of approximately 400 meV, as described elsewhere [20, 21]. Key to this work, however, are the angle resolved photoemission spectroscopy (ARPES) measurements that employed plane polarized synchrotron radiation dispersed by a 3m toroidal grating monochromator [26, 27], at the Center for Advanced Microstructures and Devices (CAMD) [28–30].…”

“…Recently, we reported fabrication and characterization of well-packed ultra-thin films made of dipolar molecules [20, 21]. Large dipole molecules tend to be good dielectrics, but obviously molecular packing and orientation can enhance or suppress the dielectric properties.…”

Simulations of Molecular Packing on a Non-Interacting Hexagonal Lattice Substrate

“…If the molecules possess intrinsic dipoles, as is the case for many molecules, the physics of the adsorption process is further complicated, by both the dipole and the frontier orbital symmetry. This has been recently demonstrated by comparing the adsorption and crystallization of the di®erent isomers of di-iodobenzene 6,7 and pentacene 8À11 as well as in the cross-linking of halogen substituted benzenes 12 on substrates where the chemisorption with the substrate is very weak. There are compelling evidences that di®erent isomers have preferential adsorption that is dependent on an interplay between symmetry and dipole.…”