The invention relates to compounds of formula I wherein M 1 , M 2 and M 3 have the meanings of claim 1, to liquid crystalline mixtures and polymers containing them, and to the use of the compounds of formula I, the liquid crystalline mixtures and the polymers containing them in optical and electrooptical devices like liquid crystal displays or projection systems, patterned films and optical elements like polarizers, retardation films, compensators, colour filters, holographic elements or polarization beam splitters, for photoswitching, in anisotropic membranes for the permeation of gases or fluids, adhesives, synthetic resins with anisotropic mechanical properties, cosmetic or pharmaceutical compositions, UV absorbers and sunscreens, diagnostics or liquid crystal pigments, for decorative and security applications, in nonlinear optics, optical information storage or as dopants.