Understanding the Adsorption Energetics of Growth Polymorphs of Ferrocene Derivatives: Microscopic Thermal Desorption Analysis

Abstract

The ultrathin films of 2-ferrocenyl-1,3-dithiolane (FcS 2 C 3 ) and 2-ferrocenyl-1,3-dithiane (FcS 2 C 4 ) dropcasted from toluene on highly oriented pyrolytic graphite (HOPG) surface are investigated using atomic force microscopy (AFM). Two types of growth polymorphs have been observed, which are distinctly different based on their nature of growth and the molecular level packing. We have developed a new type of temperature-dependent desorption experiment named "microscopic thermal desorption analysis" (MTDA) for understanding the adsorption energetics related to the observed growth polymorphs on the surface. Using MTDA, we have calculated the adsorption energies of growth polymorphs of both molecules and further revealed that their formation requires an activation energy. The subtle relation between the adsorption energies and activation energies of growth polymorphs account for their average abundance on the surface. The experimental observations are further supported by density functional theory (DFT) calculations.

Solvent‐ and Temperature‐Dependent Assembly in Monolayer Films of a Ferrocene‐Naphthyridine Hybrid on HOPG

“…The comparable relative percentage suggests, as per Boltzmann statistics, that both phases should be equally favorable (should have comparable formation energy). [17,26] This may appear contradictory to the observation made above (ambient temperature). Therefore, a question arises here about the observation of the selection of Phase-I on the surface when deposited from methanol, ethanol, acetonitrile and DMF at ambient temperature.…”

“…Statistically, this suggests that both the phases are thermodynamically driven. [17,26] c) After drop casting the film at ambient temperature, we have applied pumping for several hours to ensure proper drying or removal of solvent molecules from the films. We observed high instability while imaging the films prepared from DMF/acetonitrile after annealing.…”

“…E d , E ads and E a are the desorption energy, adsorption energy and activation barrier for the formation of Phases. The activation barrier is attributed to the associative adsorption of molecules; the energy required to rearrange molecules on the surface to reach the final adsorption geometry in a phase [17b] . ΔE a shows the difference in the activation barrier between Phase‐II and Phase‐I.…”

“…[16] Solvent controlled selection of adlayer pattern has been also shown for Fc derivatives at solid-air interface. [17] The studies related to the inclusion of conformational flexibility in the formation of adlayer patterns at the solid-air interface are scarce.…”

Revealing the Limits of Intermolecular Interactions: Molecular Rings of Ferrocene Derivatives on Graphite Surface

“…We have shown previously that 1D islands are energetically favorable compared to 2D islands. 22,23 Upon annealing, the relative abundance of 2D islands (∼35% at RT and ∼11% at 353 K) diminishes drastically compared to 1D islands (∼65% at RT and ∼64% at 353 K). In addition, it is observed that the remaining amount of 2D islands (indicated with orange lines; cf.…”