Imine Derivatives on Au(111): Evidence for “Inverted” Thermal Isomerization

Abstract

Molecules that undergo reversible isomerization between trans and cis states, typically upon illumination with light at appropriate wavelengths, represent an important class of molecular switches. In this combined scanning tunneling microscopy (STM) and high-resolution electron energy loss spectroscopy (HREELS) study, we report on self-assembled arrays of imine derivatives on a Au(111) surface. Most of the molecules are found in the trans state after deposition at room temperature, but many of them change their conformation upon heating, which we assign to switching to the cis state. As for many molecular switches, the trans isomer is the energetically more stable compound in solution, resulting in thermal cis to trans relaxation upon sufficient heating. On the surface, however, the number of cis isomers increases with temperature, pointing toward an "inverted" thermal isomerization behavior. The reason for this surface-mediated effect could be a stronger coupling, as compared to the trans state, of the central imine part of the molecule to the gold surface, which is sterically only possible in the cis state.

Presence of π…π and C H…π interactions in the new Schiff base 2-{( E )-[(3- tert -butyl-1-phenyl-1 H -pyrazol-5-yl)imino]methyl}phenol: Experimental and DFT computational studies

“…6,7 This family of compounds have widely been studied because of their interesting physicochemical properties related to their structures, this fact, have made them the object of many theoretical and experimental investigations. [8][9] The most important features of the Schiff bases or their metal complexes it can be counted: their catalytic [10][11][12] and biological activities, [13][14][15] their application as metal ion sensors, 16-18 molecular disruptor [19][20][21][22] and also as anti-cancer agents, [23][24] among others.…”

Instability-induced pattern formation of photoactivated functional polymers

“…In other words, the local concentration c of trans or cis isomers serves as morphological order parameter controlling the undulation of the surface. The tendency to form ordered islands with all molecules in the trans state has been experimentally proven by ultrahigh vacuum scanning tunneling microscopy for a monolayer of photochromic molecules on Au(111) (5). Furthermore, the electronic structure of the isomer is altered as the trans ⇀ cis photoisomerization causes an increase of the dipole moment from p trans = 0 Debye to p cis = 3 Debye (6,24) in combination with an increased electrical resistance of the isomer (4).…”

“…Since the discovery of the unique photochemical properties of azobenzene in 1937 (1), azobenzenes have been mainly used in the chemical industry. Only recently, after studies of the molecular physics of the photoisomerization of azo dyes have revealed that the photoisomerization reaction occurs on the timescale of a few picoseconds (2,3), azobenzenes came back into focus as potential photoswitchable materials (4,5). Azobenzenes have been investigated in terms of ultrafast spectroscopy (4, 6, 7), mechanoisomerization (8), the effect of slow photons (9), two-photon absorption (10) and laser-induced periodic surface structuring (11)(12)(13)(14)(15)(16)(17).…”

Island formation and manipulation of prochiral azobenzene derivatives on Au(111)

“…By exchanging the azo with a C=N Figure 1. Chemical structures of the (a) para-TBA (2,2 ,5,5 -tetra-tert-butyl-azobenzene; studied in this work) and the (b) meta-TBA ( * studied previously [9,10] group, and thus moving to imine derivatives, a quite different isomerization behavior was observed [19]. Note that the concept of trans-cis isomerization has recently been applied to molecular machines that are driven by such a chemical process [20,21].…”