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Volumn 127, Issue 41, 2005, Pages 14208-14222

Light-driven molecular motors: Stepwise thermal helix inversion during unidirectional rotation of sterically overcrowded biphenanthrylidenes

Author keywords

[No Author keywords available]

Indexed keywords

CHEMICAL BONDS; DATA ACQUISITION; ISOMERIZATION; NUCLEAR MAGNETIC RESONANCE; PHOTOCHEMICAL REACTIONS; X RAY ANALYSIS;

EID: 26844577334     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja052201e     Document Type: Article
Times cited : (72)

References (85)
  • 1
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    • Schliwa, M., Ed.; Wiley-VCH: Weinheim.
    • Molecular Motors; Schliwa, M., Ed.; Wiley-VCH: Weinheim. 2003.
    • (2003) Molecular Motors
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    • Molecular machines
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    • "Molecular Machines." Stoddart, J. F., Ed.: Special Issue. Acc. Chem. Res. 2000, 100, 409-522.
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    • Stoddart, J.F.1
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    • Photochromism: Memories and switches
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    • (b) "Photochromism: Memories and Switches." Irie, M., Ed.; Special Issue. Chem. Rev. 2000, 100, 1683-1890.
    • (2000) Chem. Rev. , vol.100 , pp. 1683-1890
    • Irie, M.1
  • 58
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    • note
    • The overall conformation of the i-propyl substituted alkene 4 is identical to that of the methyl 2 and ethyl 3 substituted alkenes. However, due to an extra carbon present in the i-propyl substituent, the priority of the substituents attached to the stereogenic center alters. Therefore, the stable trans-isomer of 4 consists of the (3S,3′S)-(P,P)-trans-4 and (3R,3′R)-(M,M)-trans-4 enantiomers and not of the (3S,3′S)-(M,M)- trans and (3R,3′R)-(P,P)-trans enantiomers as is the case with stable trans-isomers of methyl 2 and ethyl 3 substituted alkenes.
  • 66
    • 26844483814 scopus 로고    scopus 로고
    • note
    • The use of an asterisk (*) throughout this paper denotes the use of racemic compounds and is used to clarify the relation between the helicity of the molecule and the absolute configuration of the carbon atom of the stereogenic center. For example, for an alkene with a methyl substituent, (3′R*,3′R*)-(P*,P*)-trans means that the alkene is a racemic mixture of two enantiomers, (3R,3′R)-(P,P)-trans and (3S,3′S)-(M,M)-trans, of a stable frans-isomer, whereas for the same alkene, (3R*,3′R*)-(M*,M*)-trans would indicate that the molecule is a racemic mixture of an unstable trans-isomer consisting of the (3R,3′R)-(M,M)-trans and (3S,3′S)-(P,P)-trans enantiomers. From this example, it is important to note that a combination of the absolute configuration at the stereogenic carbon atom (R or S) and the overall helicity of the molecule (P or M) is only valid for certain combinations, because different isomers, stable or unstable, can be meant.
  • 69
    • 26844560782 scopus 로고    scopus 로고
    • note
    • See the Supporting Information for more detailed information.
  • 73
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    • note
    • See ref 34; the crystal structure of (3S,3′S)-(M,M)-trans-2 has been published previously and is included here for comparison.
  • 77
    • 26844468051 scopus 로고    scopus 로고
    • note
    • The absolute configuration of the enantiomerically pure alkene (35,3′S)-(M,M)-trans-2 was assigned on the basis of the stereochemical control excelled by the Evans' auxiliary. The assigned configuration was confirmed by comparison of the CD spectra of (3S,3′S)-(M,M)-trans-2 and (3R,3′R)-(P,P)-trans-1 and the CD spectra of the parent ketones.
  • 78
    • 26844518017 scopus 로고    scopus 로고
    • note
    • A chemoselective photoisomerization takes place as is evident from NMR analysis and the observation of clear isosbestic points in UV-vis and CD measurements during the photochemical steps. The quantum yields for the photochemical steps of motors 2-4 have not been determined yet. For molecular switches based on structurally related sterically overcrowded alkenes, quantum yields for photoisomerization in the range of 0.07-0.55, depending on the structure and solvent used, were found (Jager, W. F. Ph.D. Thesis, University of Groningen, 1994).
  • 79
    • 26844462989 scopus 로고    scopus 로고
    • note
    • The photochemical properties of (3S,3′S)-(M,M)-cis-2 and (3R,3′R)-(P,P)-cis-3 are expected to be identical in dodecane and n-hexane. The higher boiling point of dodecane (180 °C) is, however, suitable to determine the rate of the thermal helix inversion.
  • 80
    • 26844563245 scopus 로고    scopus 로고
    • note
    • 8.
  • 81
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    • note
    • Throughout this paper, (3S*,3′S*)-(M*.M*)- trans-4 and (3R*,3′R*)-(P*,P*)-trans-4 are referred to as unstable isomers. However, this trails-corner of 4 is stable at room temperature and is converted to the other rrans-isomers only at elevated temperatures.
  • 84
    • 26844441839 scopus 로고    scopus 로고
    • note
    • 4′.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.