Surface Vacancy Generation by STM Tunneling Electrons in the Presence of Indigo Molecules on Cu(111)

Abstract

Herein, we invesOgate the consequence of local voltage pulses on the adsorpOon state of single indigo molecules on the Cu(111) surface as well as on the atomic structure underneath the molecule. With a scanning tunneling microscope, at 5 K, intact molecules are imaged as two lobes corresponding to the electron density of each indoxyl moiety of the molecule which are connected by a carbon double bond. Then, two short successive voltage pulses with the Op placed above the molecule generate irreversible modificaOons, as revealed by consecuOve scanning tunneling microscopy (STM) imaging. Density-funcOonal theory calculaOons coupled to STM image calculaOons indicate the creaOon of a double surface vacancy of copper surface atoms below the oxygen atom of the indigo molecule as the most plausible scenario. These extracted copper atoms are stabilized as adatoms by the indigo oxygens, oxidizing each copper adatom to 0.32 electron. Introduc0onThe indigo molecule is an ancient organic dye molecule that has been used for centuries to dye colorful blue color texOles, and they even appear in recipes of Babylonian transcripts. 1 Nowadays, it is widely used as a pigment to dye billions of blue jeans per year. 2 On the other hand, due to the electronic, opOcal, and chemical properOes of the indigo molecule and its derivaOves, several applicaOons are explored such as field-effect transistors, 3,4 solar cells, 5,6 diodes, 7-9 memory storage devices, 10 diesel markers, 11 DNA biosensors, 12 or chemical detectors of NO 2 . 13 Also, the chemical structure of indigo moOvates exploring new chromophores with greater optoelectronic features. 14,15 There exist wide literature reports on indigo and its derivaOves with regard to the high photostability of the compounds. Three phenomena are invoked to account for an intramolecular change causing photostability: (1) photoexcitaOon of an excited state of the molecule for trans-cis isomerizaOon through the C═C bond; (2) isomeric change from the keto to monoenol configuraOon (Figure 1) by excited-state intramolecular proton (ESIP) transfer, where the hydrogen atom of the nitrogen atom is transferred to the oxygen; finally, (3) the isomeric dienol configuraOon resulOng from excited-state dual proton (ESDP) transfer, where both hydrogen atoms of the amine central groups are transferred to both oxygen atoms of the carbonyl groups. The first mechanism appears less favorable due to steric crowding between hydrogen atoms in the final form and the important interacOon of the hydrogen bonding between the carbonyl and N-H groups. [16][17][18][19][20] However, some thioindigo derivaOves show trans-cis isomerizaOon and the involvement of a triple state in the photoisomerizaOon 21,22 and parOcularly N,N′-di(tbutoxycarbonyl)indigo 23 shows the absence of intramolecular N-H•••O bonding. The photostability of indigo is thus been aiributed to the ESIP transfer from the keto to enol intramolecular isomerizaOon ajer irradiaOon (Figure 1), where the proton transfer occurs from the nitrogen to the oxygen atoms at th...

On‐Surface Isomerization of Indigo within 1D Coordination Polymers

“…Notably, the S-shaped protrusion is consistent with the STM imaging of indigo on Cu(111). [30] CPÀ B is comprised of a clearly distinguishable monomer: a U-shaped and a round protrusion, indicated on Figure 1a by a U-line and a dot, respectively. Interestingly, further annealing of the sample at 623 K, leads to CPs comprised predominantly of extended CPÀ B, which aggregate into self-assembled islands (see Figure S1).…”

On‐Surface Isomerization of Indigo within 1D Coordination Polymers

“…Notably, the S-shaped protrusion is consistent with the STM imaging of indigo on Cu(111). [30] CPÀ B is comprised of a clearly distinguishable monomer: a U-shaped and a round protrusion, indicated on Figure 1a by a U-line and a dot, respectively. Interestingly, further annealing of the sample at 623 K, leads to CPs comprised predominantly of extended CPÀ B, which aggregate self-assembled islands (see Figure S1).…”

Tunneling electronic excitations spatial mapping of a single graphene nanoribbon on Ag(111)

“…[18,19] The so-called ASED+ code [20] is a powerful numerical tool to describe reasonably well the structural properties of various types of molecules adsorbed on surfaces or in the gas phase. [21][22][23][24] . Standard DFT codes are not appropriate in the present case due expensive computational needs to address the 7-aGNR adsorption.…”