Homochiral helices of oligonaphthalenes inducing opposite-handed cholesteric phases.
The helical structure of the chiral nematic phases (cholesterics) obtained by doping nematic solvents with chiral non-racemic compounds is a macroscopic proof of the solute chirality. Oligonaphthalene (tetra-, hexa-, octa-) derivatives linked at the 1,4-positions have been used as chiral dopants: When the chirality axes are configurationally homogeneous (that is, all-S), the molecular structures correspond to right-handed helices. Yet, we have found series of derivatives with the surprising property that the handedness of the induced cholesteric phase alternates from positive to negative and to positive again, on passing from tetra- to hexa- and to octanaphthalene. A comparison with oligonapthalene derivatives, which do not exhibit this twisting ability, points to the importance of the substitution pattern. Both the possibility of inducing oppositely-handed cholesteric phases by homochiral helices of different length, and the role played of substituents, are confirmed by calculations performed with the surface chirality model.
Pieraccini
Silvia
S
Alma Mater Studiorum-Università di Bologna, Dipartimento di Chimica Organica A. Mangini, Via San Giacomo 11, 40126 Bologna, Italy.
Ferrarini
Alberta
A
Fuji
Kaoru
K
Gottarelli
Giovanni
G
Lena
Stefano
S
Tsubaki
Kazunori
K
Spada
Gian Piero
GP
D002942:Circular Dichroism; D008958:Models, Molecular; D008968:Molecular Conformation; D009281:Naphthalenes / Q000737:chemistry*; D013237:Stereoisomerism
D009281:Naphthalenes