Molecular engineering | EPFL Graph Search

Molecular engineering is an emerging field of study concerned with the design and testing of molecular properties, behavior and interactions in order to assemble better materials, systems, and processes for specific functions. This approach, in which observable properties of a macroscopic system are influenced by direct alteration of a molecular structure, falls into the broader category of “bottom-up” design. Molecular engineering is highly interdisciplinary by nature, encompassing aspects of chemical engineering, materials science, bioengineering, electrical engineering, physics, mechanical engineering, and chemistry. There is also considerable overlap with nanotechnology, in that both are concerned with the behavior of materials on the scale of nanometers or smaller. Given the highly fundamental nature of molecular interactions, there are a plethora of potential application areas, limited perhaps only by one's imagination and the laws of physics. However, some of the early succes

Molecular Engineering Strategies for Morphology Control in Organic Semiconductors for Optoelectronics

Muhammad Aiman Bin Rahmanudin Hamdan

It is understood that the optoelectronic performance of organic electronic devices is determinant on the macroscopic solid state self-assembly of organic semiconductors (OSC), which is driven by the supramolecular Ï-Ï stacking interactions between the conjugated segments in its molecular structure. Molecular engineering approaches directly impacts the intrinsic self-assembling properties of the OSCs, but the flexibility of organic chemistry on modulating the backbone architecture of the Ï-conjugated system has led a vast library of OSCs with various functionalities, which fundamentally changes the electronic properties of the Ï-conjugated system. It is highlighted that introducing conjugation break spacers (flexible linkers) between the Ï-conjugated segments in the OSC, showed great promise in controlling supramolecular self-assembly without altering the semiconducting core of the OSC. Previous examples on controlling the morphology of the molecular OSC, DPP(TBFu)2 using horizontal and vertical dimers, and a horizontal flexibly linked polymer analogues, have shown great promise in effecting the self-assembly behaviour and stabilizing the morphology of the parent (non-flexibly linked) DPP(TBFu)2 molecule, when used as an additive. In this thesis, an extension of this work is presented whereby the flexible linking approach is used to design and synthesize two molecular compatibilizers that consists of the donor component, DPP(TBFu)2 that is linked with an aliphatic spacer to an acceptor component, based on a fullerene and perylenediimde small molecule OSC. In chapter 2, a comparison between the compatiblizer (CP) and an in-situ linker approach (ISL) was explored to elucidate the impact of stabilizing a multi-component bulk heterojunction (BHJ) morphology and its device performance for organic photovoltaics (OPVs). It was concluded that the CP approach shows the most promise in stabilizing the BHJ morphology for OPVs, which was then applied onto a highly crystalline BHJ system with a perylenediimde acceptor to demonstrate its versatility as described in chapter 3. Taking leverage from this demonstration, chapter 4 discusses how the CP approach is used to tune the phase-domain size of the BHJ that is processed from a homogeneous single-phase melt, to obtain a photoactive BHJ in an OPV device. This unique demonstration, ultimately opens up vast new possibilities for solvent free âgreenâ processing of OPVs. Lastly in Chapter 5, the approached used to address BHJ morphological stabilization is slightly different from that of previous chapters, where the (kinetic) stability of a binary donor-acceptor BHJ is addressed. In this chapter, a fully-conjugated block copolymer (BCP) consisting of donorâacceptor blocks is used to demonstrate its applicability for a single-component BHJ for OPVs. However, the main challenge for this approach is in the synthetic methodology, and to overcome this, a modular synthetic strategy using Heck coupling between two functionalized donor and accepting marcromonomers showed promise in obtaining a fully conjugated BCP for OPVs

EPFL2018

Molecular Engineering of Electrode Surfaces for Electrocatalysis

Patrick Eduard Alexa

Electrocatalysts play an important part on the route towards environmental friendly energy sources. They support modern technologies like fuel cells to move further away from the utilization of fossil fuels and the resulting CO2 emission into our atmosphere. The main principle of such energy conversion technologies is to store chemical energy within chemical bonds and to release it as electric energy to fulfill the energy demand of today's society. However energy conversion chemistry in such technologies requires catalysts in order to be effective by providing an alternative reaction pathway that lowers activation energies and maximizes the energy output. Providing suitable catalyst surfaces requires a fundamental knowledge of the interaction of reactants and reaction intermediates with the catalyst surfaces. This concern is addressed in this thesis by fabricating specifically tailored molecular components on metal surfaces, which act as organic/inorganic hybrid electrodes for various energy conversion reactions in electrocatalysis. Characterizing the electrode surface is crucial in order to identify active sites of the catalyst. The molecular structure is investigated by surface sensitive techniques, such as STM and XPS in combination with a home-build transfer system, which enables electrode fabrication in UHV and electrocatalytic experiments in a liquid environment. A detailed characterization of organic polymer components on electrode surfaces is obtained by combining experimental data with MD simulations. The morphology of polymer networks can be successfully mimicked and depending on the chemical composition and the structure, spatial correlations on short length scales are reported. Hybrid electrodes with organic polymer co-catalysts reveal an increased catalytic activity for the HER by providing suitable docking sites that act as catalytic active sites. Reactants and reaction intermediates are stabilized via hydrogen bonding, which results in a higher catalytic turnover. The specific designed structure of the organic co-catalyst helps to identify a fraction of the reaction mechanism and highlights the importance of molecular components in electrocatalysis. The utilization of organic units on electrocatalysts provides also an excellent opportunity in order to use single metal atoms as catalysts. Engineering large pi-systems has no significant impact on the ORR activity, while the distance between active sites and the underlying electrode are crucial for enhancing the catalytic activity. A significant factor in using molecular components in electrocatalysis is the stability of the organics. Using electrografting allows to design organic/inorganic hybrid electrodes with covalent bonds between the molecular component and the metal substrate. Attaching empty porphyrin molecules to substrates introduces a powerful technique in molecular engineering, since empty porphyrin cycles can be metallized with various metal centers that can act as electrocatalysts for different electrochemical reactions. In summary, this thesis provides multiple engineering aspects, which are useful in designing molecular components on metal electrodes for energy conversion. Such hybrid catalyst surfaces are capable of improving the catalytic activity and allow to study the mechanism of catalytic reactions. Implementing organic components provides new routes for tailoring novel materials, which deliver new insight into the complex field of electrocatalysis.

EPFL2020

Enhancing Hydrogen Evolution Activity of Au(111) in Alkaline Media through Molecular Engineering of a 2D Polymer

Patrick Eduard Alexa, Klaus Kern

The electrochemical splitting of water holds promise for the storage of energy produced intermittently by renewable energy sources. The evolution of hydrogen currently relies on the use of platinum as a catalyst-which is scarce and expensive-and ongoing research is focused towards finding cheaper alternatives. In this context, 2D polymers grown as single layers on surfaces have emerged as porous materials with tunable chemical and electronic structures that can be used for improving the catalytic activity of metal surfaces. Here, we use designed organic molecules to fabricate covalent 2D architectures by an Ullmann-type coupling reaction on Au(111). The polymer-patterned gold electrode exhibits a hydrogen evolution reaction activity up to three times higher than that of bare gold. Through rational design of the polymer on the molecular level we engineered hydrogen evolution activity by an approach that can be easily extended to other electrocatalytic reactions.

WILEY-V C H VERLAG GMBH2020