Abstract:A trans-azobenzene derivative with a long alkyl chain and a TEMPO radical showed photo-induced isomerization to become the corresponding cis-isomer with a significant change of its intermolecular magnetic interaction from a weak ferromagnetic one based on the CW model to a relatively strong antiferromagnetic one based on the ST model with the J-value of 36.7 K.
“…More recently, trans ‐azobenzene derivatives carrying a nitroxide radical with some spacer units ([II] in Fig. 9a–d) were prepared and all of them showed the photo‐isomerization by irradiation in solution to the corresponding cis ‐isomers, which could be isolated as relatively stable solid substances when kept in the dark and stored in a refrigerator and reverted back to the starting trans ‐isomers when exposed to a diffused light or a fluorescent lamp for several hours (68–70).…”
Section: Dual Nitroxide Probes For Photoswitching Magnetic Materialsmentioning
Over the last decades scientists have faced growing requirements in novel methods of fast and sensitive analysis of antioxidant status of biological systems, spin redox probing and spin trapping, investigation of molecular dynamics, and of convenient models for studies of photophysical and photochemical processes. In approaching this problem, methods based upon the use of dual chromophore-nitroxide (CN) compounds have been suggested and developed. A CN consists of two molecular sub-functionality (a chromophore and a stable nitroxide radical) tethered together by spacers. In the dual compound the nitroxide is a strong intramolecular quencher of the fluorescence from the chromophore fragment. Reduction to hydroxylamine, oxidation of the nitroxide fragment or addition of an active radical yield the fluorescence increase and the parallel decay of the fragment electron spin resonance (ESR) signal. At certain conditions the dual molecules undergo photomagnetic switching and form excited state multi-spin systems. These unique properties of CN were intensively exploited as the basis for several methodologies, which include molecular probing, modeling intramolecular photochemical and photophysical processes, and construction of new magnetic materials.
“…More recently, trans ‐azobenzene derivatives carrying a nitroxide radical with some spacer units ([II] in Fig. 9a–d) were prepared and all of them showed the photo‐isomerization by irradiation in solution to the corresponding cis ‐isomers, which could be isolated as relatively stable solid substances when kept in the dark and stored in a refrigerator and reverted back to the starting trans ‐isomers when exposed to a diffused light or a fluorescent lamp for several hours (68–70).…”
Section: Dual Nitroxide Probes For Photoswitching Magnetic Materialsmentioning
Over the last decades scientists have faced growing requirements in novel methods of fast and sensitive analysis of antioxidant status of biological systems, spin redox probing and spin trapping, investigation of molecular dynamics, and of convenient models for studies of photophysical and photochemical processes. In approaching this problem, methods based upon the use of dual chromophore-nitroxide (CN) compounds have been suggested and developed. A CN consists of two molecular sub-functionality (a chromophore and a stable nitroxide radical) tethered together by spacers. In the dual compound the nitroxide is a strong intramolecular quencher of the fluorescence from the chromophore fragment. Reduction to hydroxylamine, oxidation of the nitroxide fragment or addition of an active radical yield the fluorescence increase and the parallel decay of the fragment electron spin resonance (ESR) signal. At certain conditions the dual molecules undergo photomagnetic switching and form excited state multi-spin systems. These unique properties of CN were intensively exploited as the basis for several methodologies, which include molecular probing, modeling intramolecular photochemical and photophysical processes, and construction of new magnetic materials.
“…SI-1, Figure A; SI = Supporting Information), and the corresponding cis -isomer 6b could also be isolated as a relatively stable solid. Even the azobenzenes with a long alkyl group and a TEMPO or a PROXYL group ( 7a or 8a ) were also found to occur by a similar irradiation to give the corresponding cis -isomers 7b and 8b as relatively stable solids, while irradiation on the para -substituted derivatives 9a − 12a under various conditions resulted in photobleaching and/or recovery of the starting materials in solution, and hence, the isolation of the corresponding cis -isomers was unsuccessful so far as examined in these cases. 1 (Left) Time dependence of the absorption spectra for trans -isomer 2a to cis -isomer 2b every 5 min from the original absorption in dichloromethane.…”
Section: Resultsmentioning
confidence: 99%
“…On the other hand, some cis -azobenzenes with a nitroxide group have been found to be isolable in the solid state, exhibiting differences in their magnetic properties compared with the corresponding trans -isomers. We herein describe the details of the preparation of such azobenzene derivatives carrying a nitroxide group that show photoresponsive properties together with the differences in their magnetic properties derived from the structural differences 1 1 …”
Several trans-azobenzene derivatives carrying a nitroxide (aminoxyl) radical (2a, 6a-12a) were prepared, and their photoisomerization reactions to the corresponding cis-isomers were investigated. Although no fruitful results could be obtained for the photoisomerizations of the derivatives with para-subsituents (9a-12a), the unsubstututed derivatives at the para-position (2a, 6a, 7a, 8a) were found to show photoisomerizations by irradiation to give the corresponding cis-isomers (2b, 6b, 7b, 8b), being isolated as relatively stable solid materials, and the change of the intermolecular magnetic interactions was apparently observed by the structural change for each photochromic couple.
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