Synthesis and Photochemical Characterisation of Photoactive Compounds for Molecular Electronics
Doctoral thesis, 2018
In this modern age of technology, communication is highly reliant on computing devices such as mobile phones and computers. The advent of artificial intelligence (AI) and internet of things (IoT) as well as the widespread use of user-generated contents (UGC) are demanding more computing power and large data storage. However, traditional silicon based semiconductor technology is struggling to fulfill the required infrastructure due to fundamental physics and fabrication challenges. To overcome these challenges, molecular electronics has been proposed as potentially viable solution. With judicious design, organic molecules can be synthesized with tailored properties that can emulate the functions of conventional electronics devices such as diodes, switches and transistors.
To this end, photochromic molecules attract significant attention since they can be switched with light/voltage between a less conducting and highly conducting forms. This property can be exploited to perform logic operations similar to transistors. This thesis explore the potential of norbornadiene-quadricyclane (NBD-QC)-based photochromic system, to serve as a switch for molecular electronics application. Four NBD derivatives, terminated with a thiol and thiophene groups, to enable tethering between gold electrodes, were synthesized. The compounds photochemical and photophysical properties were investigated using absorption and fluorescence spectroscopy. The results showed the compounds ability to switch between the NBD form and QC form upon photoirradiation. Moreover, the compounds were found to exhibit intrinsic emission. In particular, the long conjugated NBD form were found to be highly emissive, FF= 49%. Moreover, it was discussed that the emission can be tuned by the use of light, this makes them a potential candidate for optical memory device application. To test the robustness of the switching, more than 100 switching cycles were performed in solution and little or no degradation was observed, particularly under inert atmosphere. Additionally, the charge transport through the molecules were studied as well, using Scanning Tunneling Microscope-Break Junction (STM-BJ) technique. The results showed higher conductance values for the NBD forms and lower conductance values for the QC forms.
Furthermore, we tested the potential of 2-nitrobenzyl-based photocleavable protection group (PPG) to release terminal alkynes on plasmonic surfaces by selective light activation. The terminal alkynes may then react, for example, with azido groups embedded on nanoparticles to create a dimer linked by a single molecule. By using the tools of template self-assembly the dimers can be aligned and placed on electrodes made by lithography. Initial findings showed promising result moving us closer to create single molecule devices based on parallel fabrication.
To this end, photochromic molecules attract significant attention since they can be switched with light/voltage between a less conducting and highly conducting forms. This property can be exploited to perform logic operations similar to transistors. This thesis explore the potential of norbornadiene-quadricyclane (NBD-QC)-based photochromic system, to serve as a switch for molecular electronics application. Four NBD derivatives, terminated with a thiol and thiophene groups, to enable tethering between gold electrodes, were synthesized. The compounds photochemical and photophysical properties were investigated using absorption and fluorescence spectroscopy. The results showed the compounds ability to switch between the NBD form and QC form upon photoirradiation. Moreover, the compounds were found to exhibit intrinsic emission. In particular, the long conjugated NBD form were found to be highly emissive, FF= 49%. Moreover, it was discussed that the emission can be tuned by the use of light, this makes them a potential candidate for optical memory device application. To test the robustness of the switching, more than 100 switching cycles were performed in solution and little or no degradation was observed, particularly under inert atmosphere. Additionally, the charge transport through the molecules were studied as well, using Scanning Tunneling Microscope-Break Junction (STM-BJ) technique. The results showed higher conductance values for the NBD forms and lower conductance values for the QC forms.
Furthermore, we tested the potential of 2-nitrobenzyl-based photocleavable protection group (PPG) to release terminal alkynes on plasmonic surfaces by selective light activation. The terminal alkynes may then react, for example, with azido groups embedded on nanoparticles to create a dimer linked by a single molecule. By using the tools of template self-assembly the dimers can be aligned and placed on electrodes made by lithography. Initial findings showed promising result moving us closer to create single molecule devices based on parallel fabrication.
photoswitch
norbornadiene
photocleavable protection
Molecular electronics
KE
Opponent: Prof.Dr. Hermann A. Wegner, Justus-Liebig University Giessen, Germany
Author
Behabitu Ergette Tebikachew
Chalmers, Chemistry and Chemical Engineering, Applied Chemistry
Vårt moderna liv är starkt bereoende utav elektronik. Vi använder elektroniska enheter för att se hur vädret skall bli, läsa nyheter, ringa och skicka meddelanden till våra närstående. Den senaste tidens ökning utav användargenererat innehåll (user-generated contents, USG) i sociala medier, samt den snabba framfarten utav ny teknik såsom artificiell intelligens (AI) kräver dock kraftfulla och snabba enheter med stor datalagringskapacitet.
För närvarande är elektroniska enheter i allmänhet konstruerade enligt ‘top-down’ konceptet, dvs att man bygger de elektroniska komponenterna ifrån ett bulkmaterial. Denna teknik står inför allvarliga utmaningar på grund av fysiska begränsningar och fysikaliska lagar. Därför arbetar många forskare, inklusive vår forskargrupp, med att ta itu med dessa utmaningar genom en ’bottom-up’ metod, dvs att utgå ifrån atomer eller molekyler för att bygga upp fungerande elektroniska enheter.
I denna avhandling har jag, för att demonstrera ‘bottom-up’metoden, framställt olika organiska molekyler som kan fungera som omkopplare (switchar) för att reglera strömflöde. Molekylerna kan ha olika former, där den ena formen är mer ledande (1) och den andra mindre ledande (0). Detta betyder att vi kan skapa logiska operationer baserade på binära siffor, en metod som liknar det som används i elektronik just nu. Dessutom kan vi kan styra dessa operationer med ljus. Med våra molekyler till hands strävar vi efter att byga proof-of-concept enskilda molekylenheter baserade på organiska molekyler.
För närvarande är elektroniska enheter i allmänhet konstruerade enligt ‘top-down’ konceptet, dvs att man bygger de elektroniska komponenterna ifrån ett bulkmaterial. Denna teknik står inför allvarliga utmaningar på grund av fysiska begränsningar och fysikaliska lagar. Därför arbetar många forskare, inklusive vår forskargrupp, med att ta itu med dessa utmaningar genom en ’bottom-up’ metod, dvs att utgå ifrån atomer eller molekyler för att bygga upp fungerande elektroniska enheter.
I denna avhandling har jag, för att demonstrera ‘bottom-up’metoden, framställt olika organiska molekyler som kan fungera som omkopplare (switchar) för att reglera strömflöde. Molekylerna kan ha olika former, där den ena formen är mer ledande (1) och den andra mindre ledande (0). Detta betyder att vi kan skapa logiska operationer baserade på binära siffor, en metod som liknar det som används i elektronik just nu. Dessutom kan vi kan styra dessa operationer med ljus. Med våra molekyler till hands strävar vi efter att byga proof-of-concept enskilda molekylenheter baserade på organiska molekyler.
Our modern way of life is highly reliant on electronic devices. We use these devices to check the news and the weather, or call and send text messages to the people closest to us. However, the recent rise in user-generated contents (UGC) in social medias as well as the emergence of new technologies such as artificial intelligence (AI) are demanding powerful and fast devices with large data storage capability.
Currently, electronic device are built using the “top-down” concept i.e. building small electronic components starting from bulk material. This technology is facing serious challenges due to basic physical limitations and physics laws. Therefore, many researchers, including our research group, are working towards addressing those challenges by following the “bottom-up” approach i.e. by starting from small atoms or molecules and build up to create functioning electronic devices.
In this thesis, to demonstrate the “bottom-up” approach, we synthesised various organic molecules that can serve as a switch to regulate the flow of current. In one form, these molecules are more conducting (1) and in the other form less conducting (0). That means, we can create logic operations based on binary digits, similar to the current technology. We can regulate this operation using light. With our molecules at hand, we are aiming at building proof-of-concept “single” molecule devices based on organic molecules.
Currently, electronic device are built using the “top-down” concept i.e. building small electronic components starting from bulk material. This technology is facing serious challenges due to basic physical limitations and physics laws. Therefore, many researchers, including our research group, are working towards addressing those challenges by following the “bottom-up” approach i.e. by starting from small atoms or molecules and build up to create functioning electronic devices.
In this thesis, to demonstrate the “bottom-up” approach, we synthesised various organic molecules that can serve as a switch to regulate the flow of current. In one form, these molecules are more conducting (1) and in the other form less conducting (0). That means, we can create logic operations based on binary digits, similar to the current technology. We can regulate this operation using light. With our molecules at hand, we are aiming at building proof-of-concept “single” molecule devices based on organic molecules.
Single Molecule Nano Electronics (SIMONE)
European Commission (EC) (EC/FP7/337221), 2014-02-01 -- 2019-01-31.
Areas of Advance
Information and Communication Technology
Nanoscience and Nanotechnology (SO 2010-2017, EI 2018-)
Energy
Materials Science
Driving Forces
Sustainable development
Innovation and entrepreneurship
Subject Categories
Physical Chemistry
Physical Sciences
Chemical Sciences
Organic Chemistry
Roots
Basic sciences
Infrastructure
Chalmers Materials Analysis Laboratory
Nanofabrication Laboratory
ISBN
978-91-7597-784-3
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4465
Publisher
Chalmers
KE
Opponent: Prof.Dr. Hermann A. Wegner, Justus-Liebig University Giessen, Germany