Six structurally related crown ethers have been studied by electron impact @I) mass spectrometry. From accurate mass measurements, metastabel ion and mass-analyzed ion kinetic energy (MIKE) spectra, plausible fragmentation pathways were deduced. All compounds showed very abundant molecular ions and some amount of the doubly charged molecular ions. The primary fragmentations always involved the catechol moiety and consequent loss of oxirane although the fragment(ation)s also showed a clear dependence on the functionalities X in one of the crown ether segments, -OCH2XCHzO-(compoundfi: l/-CHz-, 2/-C=C-, 3 / t r a n s P H = CH-, 4 / c i s P H = CH-, 5/-HC+H-, and 6/-C€12CHr).Besides studies on their ability to form complexes with cations and other organic molecules, crown ethers have been subjects of a number of mass spectrometric investigation~.'-~ In the context of pursuing our studies in the chemistry and complexational behaviour of macrocyclic compoundss the electron ionization mass spectra of six closely related dibenzo crown ethers (Scheme 1) were investigated. EXPERIMENTALThe samples were synthesized as described e1~ewhere.l~ The low resolution and metastable ion spectra were recorded on a VG Analytical Ltd (Manchester, UK) MM 7070E instrument equipped with a VG 11-250 data system. The mass-analyzed ion kinetic energy (MIKE) spectra were run on a AMD 402 double focusing instrument operating at 70eV. Samples were introduced by direct inlet. The elemental composition of the main fragment ions have been confirmed by accurate mass measurements at 10 000 resolution with perfluorokerosene (PFK) as internal standard.

The 'H and I3C NMR spectra of a series of structurally related crown ethers have been recorded, and the signals assigned by means of 'H/I3C heteronuclear correlated and 'H/'H homonuclear NOE difference spectroscopy. The NMR parameters so extracted have been used to discuss the preferred, rapidly interconverting solution conformations of the studied species The high-field shifts in the I3C NMR spectra, within the so-called y-fragments, and also the 'H/'H homonuclear NOES, are particularly informative in this respect. The T, relaxation times of the I3C atoms show segmental motions within the ether segments and suggest different intramolecular flexibilities for the studied compounds.

The 'H and "C NMR spectra of a series of structurally related crown ethers were recorded, and alkali metal complexation of the crown ethers was studied for different Li, Na and K salts. The alkali metal salt-induced 'H and "C chemical shifts are discussed in terms of conformational changes within the macrocyclic ring, and the results obtained were proved to be general by means of NOE enhancement factors and spin-lattice relaxation time measurements.

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Calamitic luminophores are presented based on an elongated aryl-substituted coumarin core. The substitution pattern at terminal and lateral positions were systematically modified. The new compounds exhibit smectic C and/or nematic liquid crystalline phases. The chromophores show fluorescence in the blue spectral region. The benzopyranones are miscible with acrylate-substituted reactive nematic mesogens. Uniaxial orientation of the mixed systems was achieved by surface-assisted alignment on polyimide orientation layers. The film anisotropy was stabilised by subsequent photocrosslinking. The crosslinked oriented films display linear polarised photoluminescence upon isotropic excitation