Abstract
This thesis describes the development of a versatile synthetic protocol for preparation of a large selection of dihydroazulenes (DHAs) with both electron withdrawing and donating groups. By UV-Vis and NMR spectroscopies and even in a single-molecule junction, their ability to undergo a light-induced ring-opening reaction to vinylheptafulvenes (VHFs) and a thermally induced back-reaction (VHF → DHA) were studied in detail.
The first chapter briefly introduces photoswitches with focus, in particular, on the most well-known photoswitches. Then, the synthesis and properties of the DHA/VHF system will be discussed in detail.
The second chapter describes the design and synthesis of DHA/VHFs intended for use in molecular electronics and their solution and single-molecule junction switching properties. By the expansion of the recently reported procedure for functionalization of this system by Suzuki cross-coupling reactions, systems with either one or two “molecular alligator clips” were prepared. These were studied in solution by UV-Vis absorption spectroscopy and in a single-molecule junction, the latter by the group of Danilov and Kubatkin at the Chalmers University of Technology. A single-molecule device was prepared in which reversible switching between states of conductance could be accomplished by either light/heat or light/bias.
The third chapter describes the synthesis of a large number of donor and/or acceptor functionalized DHA/VHFs and the systematic dependence of the rate of the thermally induced back-reaction (VHF → DHA), studied by UV-Vis absorption spectroscopy. In seven different model systems, the rate of back-reaction was found to obey a Hammett correlation when plotting ln(k) against the appropriate σ-values. These plots were used to estimate the σ-value of substituents which have not yet been determined such as heteroaromatics (furan, thiophene, and 1,2,3-triazole) and alkynes (triisopropylsilylethyne, trimethylsilyl- 1,3-butadiyne, and 1,3-butadiyne). It was also shown that the absorption maximum of the VHF and the rate of back-reaction can be conveniently fine-tuned by these donor or acceptor groups.
The fourth chapter describes the synthesis and study of a VHF containing two sites for ring-closure in an attempt to overcome the problem of the VHF taking an unreactive conformation which was speculated to cause the relatively slow back-reaction (VHF → DHA). The study showed that the rate of back-reaction was increased with close to a factor of 2 which is only the statistical improvement of having two possible sites for back-reaction as supposed to just one.
The fifth chapter describes, in short, my contributions to an additional seven papers published.
Figure 1. Structure of proposed transition state (TS) for the thermally induced ring-closure (VHF → DHA). This strongly polarized TS is responsible for substituent-dependency of this reaction (left). Reversible switching between the states of the DHA/VHF trapped in a silver nano-gap (right).
The first chapter briefly introduces photoswitches with focus, in particular, on the most well-known photoswitches. Then, the synthesis and properties of the DHA/VHF system will be discussed in detail.
The second chapter describes the design and synthesis of DHA/VHFs intended for use in molecular electronics and their solution and single-molecule junction switching properties. By the expansion of the recently reported procedure for functionalization of this system by Suzuki cross-coupling reactions, systems with either one or two “molecular alligator clips” were prepared. These were studied in solution by UV-Vis absorption spectroscopy and in a single-molecule junction, the latter by the group of Danilov and Kubatkin at the Chalmers University of Technology. A single-molecule device was prepared in which reversible switching between states of conductance could be accomplished by either light/heat or light/bias.
The third chapter describes the synthesis of a large number of donor and/or acceptor functionalized DHA/VHFs and the systematic dependence of the rate of the thermally induced back-reaction (VHF → DHA), studied by UV-Vis absorption spectroscopy. In seven different model systems, the rate of back-reaction was found to obey a Hammett correlation when plotting ln(k) against the appropriate σ-values. These plots were used to estimate the σ-value of substituents which have not yet been determined such as heteroaromatics (furan, thiophene, and 1,2,3-triazole) and alkynes (triisopropylsilylethyne, trimethylsilyl- 1,3-butadiyne, and 1,3-butadiyne). It was also shown that the absorption maximum of the VHF and the rate of back-reaction can be conveniently fine-tuned by these donor or acceptor groups.
The fourth chapter describes the synthesis and study of a VHF containing two sites for ring-closure in an attempt to overcome the problem of the VHF taking an unreactive conformation which was speculated to cause the relatively slow back-reaction (VHF → DHA). The study showed that the rate of back-reaction was increased with close to a factor of 2 which is only the statistical improvement of having two possible sites for back-reaction as supposed to just one.
The fifth chapter describes, in short, my contributions to an additional seven papers published.
Figure 1. Structure of proposed transition state (TS) for the thermally induced ring-closure (VHF → DHA). This strongly polarized TS is responsible for substituent-dependency of this reaction (left). Reversible switching between the states of the DHA/VHF trapped in a silver nano-gap (right).
| Originalsprog | Engelsk |
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| Forlag | Department of Chemistry, Faculty of Science, University of Copenhagen |
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| Antal sider | 137 |
| Status | Udgivet - 2013 |