Periodic Reporting for period 1 - Photo SCO LCs (Photoresponsive spin-crossover liquid crystals)
Okres sprawozdawczy: 2021-11-01 do 2023-10-31
Since the end of the 20th century, digital information has been permeating every aspect of our lives and society, leading to the exploding growth of information production. A recent study reported the total amount of data created, captured, copied and consumed worldwide in 2018 was 33 zettabytes (ZB), equivalent to 33 trillion gigabytes (GB). In 2020, this number grows to 59 ZB and is expected to reach an unimaginable 175 ZB by 2025. Therefore, scientists face a big challenge to develop more lightweight and high-density information storage materials.
With the rapid development of the field of microelectronics, electronic components at the molecular level have attracted more and more attention and become one of the research hotspots in materials science. Professor O. Kahn has defined bistability at the molecular level as follows: molecular bistability means that under certain external conditions, the molecule will exist two stable or metastable electronic states. Spin-crossover (SCO) complex is a kind of typical bistable material, which can change electron configuration between high spin (HS) state and low spin (LS) state in response to light, temperature, pressure and other external stimuli, resulting in a series of physical and chemical properties such as magnetism, color, dielectric constant, density and so on. As a result, the high-low spin state is compared to the binary encoding 0 and 1 in electronics and show attractive application prospect in the fields of information storage.
Since the first observation of SCO behavior in a mononuclear Fe(III) complex in 1932, numerous SCO complexes with different SCO characteristic, such as abruptness, step and hysteresis, have be observed. At present, most of the research on SCO is mainly limited to the properties of the crystalline compounds themselves, however, the research on SCO functional devices has been difficult because the mechanical strength and processing properties of SCO materials are limited by the nature of their coordination compounds. Therefore, the developing of soft SCO materials are of particular importance to realize the industrial application. For obtained this goal, the combination of SCO behaviour with liquid crystal (LC) properties in a single material has been preliminarily explored by researchers because of the advantages in potential applications such as process ability in thin films. In 2001, Galyametdinov et al reported the first example of coexistence of thermal spin transition and liquid-crystal (LC) properties. The compound displays a gradual spin conversion between 300 and 80 K, while the smectic phase forms around 400 K. This study first demonstrated the possibility of coexistence of spin crossover and liquid-crystalline (LC) properties in a single compound. This result motivated several groups to decorate the long alkyl chain on the SCO molecules to obtain the SCO LCs and study the synergy between SCO and LC properties. However, so far, the reported examples are still rare.
In 2018, the hosting group at Centre de Recherche Paul Pascal (CRPP), in collaboration with Institute for Solid State Chemistry Bordeaux (ICMCB) has used this strategy and synthesized mononuclear Fe(II) based SCO molecules with decyl chains to demonstrate the synergetic behavior between conformational changes of alkyl groups and SCO behavior. Based on the preliminary work, the objective of this fellowship was to modify the decoration position and numbers of alkyl groups to realize the LCs in the selected SCO molecular system. Then, by introducing photochromic azobenzene group in the system, the spin state of SCO molecules could be optically controlled through structural trans-cis photoisomerism.
With the rapid development of the field of microelectronics, electronic components at the molecular level have attracted more and more attention and become one of the research hotspots in materials science. Professor O. Kahn has defined bistability at the molecular level as follows: molecular bistability means that under certain external conditions, the molecule will exist two stable or metastable electronic states. Spin-crossover (SCO) complex is a kind of typical bistable material, which can change electron configuration between high spin (HS) state and low spin (LS) state in response to light, temperature, pressure and other external stimuli, resulting in a series of physical and chemical properties such as magnetism, color, dielectric constant, density and so on. As a result, the high-low spin state is compared to the binary encoding 0 and 1 in electronics and show attractive application prospect in the fields of information storage.
Since the first observation of SCO behavior in a mononuclear Fe(III) complex in 1932, numerous SCO complexes with different SCO characteristic, such as abruptness, step and hysteresis, have be observed. At present, most of the research on SCO is mainly limited to the properties of the crystalline compounds themselves, however, the research on SCO functional devices has been difficult because the mechanical strength and processing properties of SCO materials are limited by the nature of their coordination compounds. Therefore, the developing of soft SCO materials are of particular importance to realize the industrial application. For obtained this goal, the combination of SCO behaviour with liquid crystal (LC) properties in a single material has been preliminarily explored by researchers because of the advantages in potential applications such as process ability in thin films. In 2001, Galyametdinov et al reported the first example of coexistence of thermal spin transition and liquid-crystal (LC) properties. The compound displays a gradual spin conversion between 300 and 80 K, while the smectic phase forms around 400 K. This study first demonstrated the possibility of coexistence of spin crossover and liquid-crystalline (LC) properties in a single compound. This result motivated several groups to decorate the long alkyl chain on the SCO molecules to obtain the SCO LCs and study the synergy between SCO and LC properties. However, so far, the reported examples are still rare.
In 2018, the hosting group at Centre de Recherche Paul Pascal (CRPP), in collaboration with Institute for Solid State Chemistry Bordeaux (ICMCB) has used this strategy and synthesized mononuclear Fe(II) based SCO molecules with decyl chains to demonstrate the synergetic behavior between conformational changes of alkyl groups and SCO behavior. Based on the preliminary work, the objective of this fellowship was to modify the decoration position and numbers of alkyl groups to realize the LCs in the selected SCO molecular system. Then, by introducing photochromic azobenzene group in the system, the spin state of SCO molecules could be optically controlled through structural trans-cis photoisomerism.
The fellow firstly compares the relationship between the decoration of alkyl groups ligands and the corresponding magnetic properties for the obtained mononuclear Fe(II) complex. It was found decoration of the alkyl groups on the pyridine group will always lead to a disappearance of SCO properties and only HS state was observed due to the weak ligand field. Thus, for retaining the SCO properties, it was better to introduce the alkyl groups at the groups which are far from the SCO center. On the other hand, several obtained Fe(II) complexes display interesting SCO behavior. During the SCO process, the structural isomerism of the alkyl groups was observed, showing a synergy effect between SCO and structural isomerism. Moreover, this compound can be then photo excited to give the initial paramagnetic state. This part of work is under preparation and will be published in the future.
The results on alkyl chain decorated mononuclear Fe(II) SCO Analogues have been presented in the following conferences: Scientific conferences Les journées scientifiques de l’Association Française de Magnétisme Moléculaire JAM2 2022 (22-24 November 2022, Dourdan, France) and The 18th International Conference on Molecule-Based Magnets (10-14 September 2023, Nanjing, China). The results have been presented in two joint group meetings to the collaborated teams in ICMCB and several visiting researchers.
The results on alkyl chain decorated mononuclear Fe(II) SCO Analogues have been presented in the following conferences: Scientific conferences Les journées scientifiques de l’Association Française de Magnétisme Moléculaire JAM2 2022 (22-24 November 2022, Dourdan, France) and The 18th International Conference on Molecule-Based Magnets (10-14 September 2023, Nanjing, China). The results have been presented in two joint group meetings to the collaborated teams in ICMCB and several visiting researchers.
Through the decoration of hydrazone ligands with alkyl groups, the effect of the decoration position and numbers on SCO and LC properties were studied in detail, and thus directing the further designing of Fe(II) SCO LCs complexes. Additionally, we observed the synergy effect between the spin state and alkane chain configuration isomerism, which could be potentially used to control the spin state of SCO complexes. However, it should be noted that the SCO LCs project deals with fundamental research and there is no expected short-term potential impact at this moment.