Tatiana Fernandez Landaluce

Light-driven altitudinal molecular motors on surfaces

A Cu(I)-catalyzed 1,3-dipolar cycloaddition was used to construct a monolayer of an altitudinal molecular motor on quartz and silicon substrates, which represents the fastest light-driven molecular motor, to date, grafted to a solid surface.

Photochromism and Electrochemistry of a Dithienylcyclopentene Electroactive Polymer

A bifunctional substituted dithienylcyclopentene photochromic switch bearing electropolymerisable methoxystyryl units, which enable immobilization of the photochromic unit on conducting substrates, is reported. The spectroscopic, electrochemical, and photochemical properties of a monomer in solution are compared with those of the polymer formed through oxidative electropolymerization. The electroactive polymer films prepared on gold, platinum, glassy carbon, and indium titanium oxide (ITO) electrodes were characterized by cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The thickness of the films formed is found to be limited to several monolayer equivalents. The photochromic properties and stability of the polymer films have been investigated by UV/vis spectroscopy, electrochemistry, and XPS. Although the films are electrochemically and photochemically stable, their mechanical stability with respect to adhesion to the electrode was found to be sensitive to both the solvent and the electrode material employed, with more apolar solvents, glassy carbon, and ITO electrodes providing good adhesion of the polymer film. The polymer film is formed consistently as a thin film and can be switched both optically and electrochemically between the open and closed state of the photochromic dithienylethene moiety.

Adhesion of Photon-Driven Molecular Motors to Surfaces via 1,3-Dipolar Cycloadditions: Effect of Interfacial Interactions on Molecular Motion

We report the attachment of altitudinal light-driven molecular motors to surfaces using 1,3-dipolar cycloaddition reactions. Molecular motors were designed containing azide or alkyne groups for attachment to alkyne- or azide-modified surfaces. Surface attachment was characterized by UV-vis, IR, XPS, and ellipsometry measurements. Surface-bound motors were found to undergo photochemical and thermal isomerizations consistent with unidirectional rotation in solution. Confinement at a surface was found to reduce the rate of the thermal isomerization process. The rate of thermal isomerization was also dependent on the surface coverage of the motors. In solution, changes in the UV-vis signal that accompany thermal isomerization can be fit with a single monoexponential decay. In contrast, thermal isomerization of the surface-bound motors does not follow a single monoexponential decay and was found to fit a biexponential decay. Both one- and two-legged motors were attached to surfaces. The kinetics of thermal isomerization was not affected by the valency of attachment, indicating that the changes in kinetics from solution to surface systems are related to interactions between the surface-bound motors.

Intermolecular repulsion through interfacial attraction: toward engineering of polymorphs.

Understanding the formation of crystalline polymorphs is of importance for various applications of materials science. Polymorphism of Schiff base derivatives has recently attracted considerable attention because of its influence on photochromic and thermochromic properties of their 3D crystals. The present investigation extends the study of Schiff base polymorphism to the molecular level by using a combination of scanning tunneling microscopy at the liquid/solid interface and molecular modeling. It is demonstrated that polymorphism of 4-(dodecyloxy)-N-(4-dodecylphenyl)-2-hydroxybenzaldimine (PHB), a Schiff base substituted by alkyl side chains, can occur in 2D crystals when PHB is adsorbed on a surface that is able to exchange charge with the molecule. In particular, on Au(111), PHB molecules self-organize not only into a columnar packing but also in dimer structures. Theoretical and experimental results demonstrate that the dimer-based structure observed on Au(111) originates from molecule/surface interactions, which in turn modify molecule/molecule interactions. The results highlight that the Au(111) substrate is far from being a passive part of the self-assembled system and plays a crucial role in the morphology of 2D polymorphs.

Rotary Molecular Motors: A Large Increase in Speed through a Small Change in Design

Reducing the steric interaction between the upper-half and the lower-half of a light-driven rotary molecular motor by decreasing the size of the aromatic moiety in the upper-half from a naphthalene to a benzothiophene results in an almost 3500 times faster rotation.