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Photoinversion of cisoid/transoid binaphthyls
Kazuto Takaishi1, Atsuya Muranaka, Masuki Kawamoto
1RIKEN, Hirosawa 2-1, Wako, Saitama 351-0198, Japan. ktakaishi@riken.jp
Organic Letters
|December 14, 2011
Summary
Synthesized novel binaphthyl-azobenzene cyclic dyads. Photoirradiation induced significant changes in circular dichroism and optical rotation, revealing a strong coupling between azobenzene photoisomerization and binaphthyl dihedral angles.
Area of Science:
- Organic Chemistry
- Photochemistry
- Supramolecular Chemistry
Background:
- Axially chiral molecules like binaphthyl derivatives are crucial in asymmetric synthesis and molecular recognition.
- Azobenzene-containing compounds are widely studied for their photoresponsive properties and potential in molecular switches.
- The integration of chiral scaffolds with photochromic units offers opportunities for developing advanced functional materials.
Purpose of the Study:
- To synthesize novel axially chiral binaphthyl-azobenzene cyclic dyads with varying linker lengths.
- To investigate the impact of photoirradiation on the circular dichroism (CD) spectrum and optical rotation of these dyads.
- To elucidate the relationship between azobenzene photoisomerization and the conformational changes of the binaphthyl moiety.
Main Methods:
- Synthesis of binaphthyl-azobenzene cyclic dyads via established organic synthesis protocols.
- Photochemical studies involving UV-Vis spectroscopy and irradiation to induce azobenzene isomerization.
- Chiroptical measurements including circular dichroism (CD) spectroscopy and polarimetry.
- Computational modeling (e.g., Density Functional Theory) to analyze structural and electronic properties.
Main Results:
- Successful synthesis of binaphthyl-azobenzene cyclic dyads connected by linkers of differential lengths.
- Photoirradiation of benzylated-binaphthyl analogue 2b led to substantial alterations in its CD spectrum and optical rotation.
- Experimental and theoretical analyses demonstrated a strong coupling: cis-azobenzene induced a transoid binaphthyl structure, while trans-azobenzene induced a cisoid binaphthyl structure.
Conclusions:
- The synthesized binaphthyl-azobenzene cyclic dyads exhibit photo-tunable chiroptical properties.
- Azobenzene photoisomerization effectively controls the dihedral angle of the binaphthyl unit within the cyclic structure.
- These findings pave the way for designing sophisticated photoresponsive chiral materials and molecular switches.
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