Development of Norbornadiene Photoswitches for Molecular Solar Thermal Energy Storage

Mads Mansø

Development of Norbornadiene Photoswitches for Molecular Solar Thermal Energy Storage

Mads Mansø

Abstract

This thesis describes the synthesis and characterization of the properties of a large array of different functionalized norbornadienes (NBDs) aimed at optimising the properties for their use as a molecular solar thermal (MOST) systems. This includes; 1) optimization of the absorption spectrum to match the solar spectrum; 2) optimization of the photoisomerization quantum yield; 3) increasing the energy density of the metastable quadricyclane (QC) isomer. The first chapter gives a brief introduction to photochromism and the potentials of different photoswitches for the use in MOST systems, particularly with a focus on the NBD - QC photo/thermo-couple. The second chapter describes the synthesis of a series of dithiafulvene (DTF) functionalized NBDs with significantly redshifted absorption onsets (lonset) of up to 556 nm. Here a limit in the possible redshift of absorption, while maintaining a photoswitchable NBD unit, is existing. The least redshifted derivative showed reversible switching to the QC isomer, whereas no switching was observed for the most redshifted derivatives. This was rationalized by a computational study performed by collaborators. The third chapter includes the synthesis and spectroscopic characterization of two series of NBD oligomers linked by a shared donor-group. One of the series with carbon-based linkers showed increased absorption onsets, photoisomerization quantum yields as high as 94% and energy densities up to 559 kJ/kg. Exchanging the linker unit to heteroaryl-based donors (thiophene or carbazole) resulted in an even more redshifted absorption, with onsets as high as 468 nm. The fourth chapter describes the synthesis of a large array of cyano-aryl NBDs with varying aryl groups synthesized by a convenient, transition-metal free and scalable synthetic route in four steps. Among this series of 17 new NBDs it was found that substituents on the ortho-position of the aryl group resulted in greatly increased half-lives of the QC isomers. The fifth chapter involves a thorough investigation of the kinetics of the QC to NBD conversion. The basis was an expansion of the series of NBDs described in Chapter 4, affording 18 different para- or meta-substituted NBDs. By a Hammett correlation it was indicated that the isomerization from QC to NBD proceeds in a radical mechanism. The sixth chapter describes the synthesis of a series of benzo- and naphthofused NBDs in an attempt at stabilizing the NBD isomers, reaching higher energy storage potentials (difference in DHQC and DHNBD). It was found that the stability of the NBD was enhanced to such a degree that irradiation led only to decomposition, as opposed to isomerization to the corresponding QC. The synthesis of a phenanthrene analogue was initiated. The seventh chapter involves the synthesis of a series of six fused NBD - dihydroazulene (DHA) systems in collaboration with PhD student Martin Drøhse Kilde. Here it was found that switching of the individual photochromic components reaching the QC-VHF state could only be achieved for a selection of the derivatives, and the isomerization of the NBD component prior to the DHA component reaching the QC-DHA state was not possible for any of the systems. It was clear that the choice of linker has a detrimental impact on the sequential switching properties of the system.

Originalsprog	Engelsk

Forlag	Department of Chemistry, Faculty of Science, University of Copenhagen
Status	Udgivet - 2019

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title = "Development of Norbornadiene Photoswitches for Molecular Solar Thermal Energy Storage",

abstract = "This thesis describes the synthesis and characterization of the properties of a large array of different functionalized norbornadienes (NBDs) aimed at optimising the properties for their use as a molecular solar thermal (MOST) systems. This includes; 1) optimization of the absorption spectrum to match the solar spectrum; 2) optimization of the photoisomerization quantum yield; 3) increasing the energy density of the metastable quadricyclane (QC) isomer. The first chapter gives a brief introduction to photochromism and the potentials of different photoswitches for the use in MOST systems, particularly with a focus on the NBD - QC photo/thermo-couple. The second chapter describes the synthesis of a series of dithiafulvene (DTF) functionalized NBDs with significantly redshifted absorption onsets (lonset) of up to 556 nm. Here a limit in the possible redshift of absorption, while maintaining a photoswitchable NBD unit, is existing. The least redshifted derivative showed reversible switching to the QC isomer, whereas no switching was observed for the most redshifted derivatives. This was rationalized by a computational study performed by collaborators. The third chapter includes the synthesis and spectroscopic characterization of two series of NBD oligomers linked by a shared donor-group. One of the series with carbon-based linkers showed increased absorption onsets, photoisomerization quantum yields as high as 94% and energy densities up to 559 kJ/kg. Exchanging the linker unit to heteroaryl-based donors (thiophene or carbazole) resulted in an even more redshifted absorption, with onsets as high as 468 nm. The fourth chapter describes the synthesis of a large array of cyano-aryl NBDs with varying aryl groups synthesized by a convenient, transition-metal free and scalable synthetic route in four steps. Among this series of 17 new NBDs it was found that substituents on the ortho-position of the aryl group resulted in greatly increased half-lives of the QC isomers. The fifth chapter involves a thorough investigation of the kinetics of the QC to NBD conversion. The basis was an expansion of the series of NBDs described in Chapter 4, affording 18 different para- or meta-substituted NBDs. By a Hammett correlation it was indicated that the isomerization from QC to NBD proceeds in a radical mechanism. The sixth chapter describes the synthesis of a series of benzo- and naphthofused NBDs in an attempt at stabilizing the NBD isomers, reaching higher energy storage potentials (difference in DHQC and DHNBD). It was found that the stability of the NBD was enhanced to such a degree that irradiation led only to decomposition, as opposed to isomerization to the corresponding QC. The synthesis of a phenanthrene analogue was initiated. The seventh chapter involves the synthesis of a series of six fused NBD - dihydroazulene (DHA) systems in collaboration with PhD student Martin Dr{\o}hse Kilde. Here it was found that switching of the individual photochromic components reaching the QC-VHF state could only be achieved for a selection of the derivatives, and the isomerization of the NBD component prior to the DHA component reaching the QC-DHA state was not possible for any of the systems. It was clear that the choice of linker has a detrimental impact on the sequential switching properties of the system.",

author = "Mads Mans{\o}",

year = "2019",

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publisher = "Department of Chemistry, Faculty of Science, University of Copenhagen",

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N2 - This thesis describes the synthesis and characterization of the properties of a large array of different functionalized norbornadienes (NBDs) aimed at optimising the properties for their use as a molecular solar thermal (MOST) systems. This includes; 1) optimization of the absorption spectrum to match the solar spectrum; 2) optimization of the photoisomerization quantum yield; 3) increasing the energy density of the metastable quadricyclane (QC) isomer. The first chapter gives a brief introduction to photochromism and the potentials of different photoswitches for the use in MOST systems, particularly with a focus on the NBD - QC photo/thermo-couple. The second chapter describes the synthesis of a series of dithiafulvene (DTF) functionalized NBDs with significantly redshifted absorption onsets (lonset) of up to 556 nm. Here a limit in the possible redshift of absorption, while maintaining a photoswitchable NBD unit, is existing. The least redshifted derivative showed reversible switching to the QC isomer, whereas no switching was observed for the most redshifted derivatives. This was rationalized by a computational study performed by collaborators. The third chapter includes the synthesis and spectroscopic characterization of two series of NBD oligomers linked by a shared donor-group. One of the series with carbon-based linkers showed increased absorption onsets, photoisomerization quantum yields as high as 94% and energy densities up to 559 kJ/kg. Exchanging the linker unit to heteroaryl-based donors (thiophene or carbazole) resulted in an even more redshifted absorption, with onsets as high as 468 nm. The fourth chapter describes the synthesis of a large array of cyano-aryl NBDs with varying aryl groups synthesized by a convenient, transition-metal free and scalable synthetic route in four steps. Among this series of 17 new NBDs it was found that substituents on the ortho-position of the aryl group resulted in greatly increased half-lives of the QC isomers. The fifth chapter involves a thorough investigation of the kinetics of the QC to NBD conversion. The basis was an expansion of the series of NBDs described in Chapter 4, affording 18 different para- or meta-substituted NBDs. By a Hammett correlation it was indicated that the isomerization from QC to NBD proceeds in a radical mechanism. The sixth chapter describes the synthesis of a series of benzo- and naphthofused NBDs in an attempt at stabilizing the NBD isomers, reaching higher energy storage potentials (difference in DHQC and DHNBD). It was found that the stability of the NBD was enhanced to such a degree that irradiation led only to decomposition, as opposed to isomerization to the corresponding QC. The synthesis of a phenanthrene analogue was initiated. The seventh chapter involves the synthesis of a series of six fused NBD - dihydroazulene (DHA) systems in collaboration with PhD student Martin Drøhse Kilde. Here it was found that switching of the individual photochromic components reaching the QC-VHF state could only be achieved for a selection of the derivatives, and the isomerization of the NBD component prior to the DHA component reaching the QC-DHA state was not possible for any of the systems. It was clear that the choice of linker has a detrimental impact on the sequential switching properties of the system.

AB - This thesis describes the synthesis and characterization of the properties of a large array of different functionalized norbornadienes (NBDs) aimed at optimising the properties for their use as a molecular solar thermal (MOST) systems. This includes; 1) optimization of the absorption spectrum to match the solar spectrum; 2) optimization of the photoisomerization quantum yield; 3) increasing the energy density of the metastable quadricyclane (QC) isomer. The first chapter gives a brief introduction to photochromism and the potentials of different photoswitches for the use in MOST systems, particularly with a focus on the NBD - QC photo/thermo-couple. The second chapter describes the synthesis of a series of dithiafulvene (DTF) functionalized NBDs with significantly redshifted absorption onsets (lonset) of up to 556 nm. Here a limit in the possible redshift of absorption, while maintaining a photoswitchable NBD unit, is existing. The least redshifted derivative showed reversible switching to the QC isomer, whereas no switching was observed for the most redshifted derivatives. This was rationalized by a computational study performed by collaborators. The third chapter includes the synthesis and spectroscopic characterization of two series of NBD oligomers linked by a shared donor-group. One of the series with carbon-based linkers showed increased absorption onsets, photoisomerization quantum yields as high as 94% and energy densities up to 559 kJ/kg. Exchanging the linker unit to heteroaryl-based donors (thiophene or carbazole) resulted in an even more redshifted absorption, with onsets as high as 468 nm. The fourth chapter describes the synthesis of a large array of cyano-aryl NBDs with varying aryl groups synthesized by a convenient, transition-metal free and scalable synthetic route in four steps. Among this series of 17 new NBDs it was found that substituents on the ortho-position of the aryl group resulted in greatly increased half-lives of the QC isomers. The fifth chapter involves a thorough investigation of the kinetics of the QC to NBD conversion. The basis was an expansion of the series of NBDs described in Chapter 4, affording 18 different para- or meta-substituted NBDs. By a Hammett correlation it was indicated that the isomerization from QC to NBD proceeds in a radical mechanism. The sixth chapter describes the synthesis of a series of benzo- and naphthofused NBDs in an attempt at stabilizing the NBD isomers, reaching higher energy storage potentials (difference in DHQC and DHNBD). It was found that the stability of the NBD was enhanced to such a degree that irradiation led only to decomposition, as opposed to isomerization to the corresponding QC. The synthesis of a phenanthrene analogue was initiated. The seventh chapter involves the synthesis of a series of six fused NBD - dihydroazulene (DHA) systems in collaboration with PhD student Martin Drøhse Kilde. Here it was found that switching of the individual photochromic components reaching the QC-VHF state could only be achieved for a selection of the derivatives, and the isomerization of the NBD component prior to the DHA component reaching the QC-DHA state was not possible for any of the systems. It was clear that the choice of linker has a detrimental impact on the sequential switching properties of the system.

UR - https://rex.kb.dk/primo-explore/fulldisplay?docid=KGL01012010255&context=L&vid=NUI&search_scope=KGL&tab=default_tab&lang=da_DK

M3 - Ph.D. thesis

BT - Development of Norbornadiene Photoswitches for Molecular Solar Thermal Energy Storage

PB - Department of Chemistry, Faculty of Science, University of Copenhagen

ER -