Development of new materials for information storage and retrieval at the molecular level offers a formidable challenge toward future technology. Azobenzene compounds are excellent candidates for the design of new molecular motors, their potential lies on the light-driven reversible isomerisation process upon a determinate wavelength radiation. This proposal is directed toward the application of a synthesis of chiral aromatic azobezene compounds. The method provides significant advantages due to the mild reaction conditions required and the accessibility of the starting materials: quinone acetals and aryl hydrazines. One of the more exciting aspects of this study that we will emphasize is the synthesis of azobenzenes with central and helical chirality. Despite the extensive use of sulfoxides in asymmetric synthesis, there are no examples of its incorporation in chiral molecular switches. Other chiral groups such as helicene derivatives will be also studied. The cis-trans photoisomerization of the resulting azobenzenes will be explored by irradiation with light of different wavelengths in solvents of different polarity and in Liquid Crystalline phases. The behavior deduced from this study will allow to design new structures for the applications of such systems as new chiroptical molecular switches. The photoisomerisation process will be investigated also in nematic liquid crystalline phases. It is well known that doping a nematic phase with a chiral non-racemic compound transforms it into a cholesteric (chiral) phase. When the chiral dopant contains a photoactive unit (as the azo group) the photoisomerisation will allow to modulate the optical properties of the LC phases. In particular a photochromic effect connected to the variation of the cholesteric pitch may be observed. This might lead to the possibility on writing and erasing on a LC matrix as well as of obtaining memory effect and tracing the thermal history of the sample.
Synthesis and photochromic properties of chiral aromatic azocompounds
SPADA, GIAN PIERO
2005
Abstract
Development of new materials for information storage and retrieval at the molecular level offers a formidable challenge toward future technology. Azobenzene compounds are excellent candidates for the design of new molecular motors, their potential lies on the light-driven reversible isomerisation process upon a determinate wavelength radiation. This proposal is directed toward the application of a synthesis of chiral aromatic azobezene compounds. The method provides significant advantages due to the mild reaction conditions required and the accessibility of the starting materials: quinone acetals and aryl hydrazines. One of the more exciting aspects of this study that we will emphasize is the synthesis of azobenzenes with central and helical chirality. Despite the extensive use of sulfoxides in asymmetric synthesis, there are no examples of its incorporation in chiral molecular switches. Other chiral groups such as helicene derivatives will be also studied. The cis-trans photoisomerization of the resulting azobenzenes will be explored by irradiation with light of different wavelengths in solvents of different polarity and in Liquid Crystalline phases. The behavior deduced from this study will allow to design new structures for the applications of such systems as new chiroptical molecular switches. The photoisomerisation process will be investigated also in nematic liquid crystalline phases. It is well known that doping a nematic phase with a chiral non-racemic compound transforms it into a cholesteric (chiral) phase. When the chiral dopant contains a photoactive unit (as the azo group) the photoisomerisation will allow to modulate the optical properties of the LC phases. In particular a photochromic effect connected to the variation of the cholesteric pitch may be observed. This might lead to the possibility on writing and erasing on a LC matrix as well as of obtaining memory effect and tracing the thermal history of the sample.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
