Oriented inclusion complexes of chloroform@cryptophane-A and chloroform@bis-cryptophane were prepared using a nematic thermotropic liquid crystal (ZLI 1132), and the alignment and magnetic resonance properties of these host-guest systems were studied via 13C NMR of the labeled guests. Large 1H-13C dipolar splittings for 13CHCl3 guests indicated significantly enhanced (∼2-fold) ordering for the trapped vs. free ligands under all conditions studied, with similar ordering observed for the two complexes - despite significant differences in size and motional freedom between the hosts. For each environment, variable-temperature studies permitted the sign and magnitude of the order parameter for chloroform's C-H bond to be independently determined from the 13C chemical shift anisotropy (CSA) shifts (via the gradient method) and the restored 1H-13C dipolar couplings. In both systems, the results are consistent with overall alignment of the complexes such that the cage principal axis lies roughly perpendicular to the LC director.
Bibliographical noteFunding Information:
It is a pleasure to acknowledge our colleagues, Prof. Jean-Pierre Dutasta and Dr. Thierry Brotin (ENS Lyon), for their assistance, and for generously providing samples of cryptophane-A and bis -cryptophane. We thank Prof. Jukka Jokisaari (U. Oulu) for helpful correspondence concerning the use of the gradient method, and Prof. Cynthia Jameson (UIC) for helpful discussions. B.M.G. is a Cottrell Scholar of Research Corporation. Work at SIUC is supported by the National Science Foundation (CAREER Award, Grant No. CHE-03492550), the ACS Petroleum Research Fund, Research Corporation, the Oak Ridge Associated Universities (ORAU), and SIUC's Materials Technology Center and Office of Research Development and Administration (ORDA).
- Dipolar couplings
- Dynamic coupling
- Gradient method
- Inclusion complexes
- Liquid crystals
- ZLI 1132