The present invention relates to a photoaligning compound of formula (I), to a process for the preparation of this compound, to a photoaligning composition, obtained by this process, to the use of said compositions as orienting layer for liquid crystals and in the construction of unstructured and structured optical elements and multi-layer systems, especially liquid crystal displays.

Optionally polymerizable mesogen compounds are disclosed that include a polyvalent non-mesogenic core X to which is bonded three or four separate extensions, where each extension independently includes, in sequence, a linking group -L-, and a mesogen group[Mesogen]. The mesogen compounds are represented by the following Formula (I), ##STR00001##
With reference to Formula (I), v is 3 or 4; t is 0 or 1; at least one Mesogen includes at least four cyclic groups; each -L- independently has an average chain length of at least 15 bonds; and at least one -L- has an average chain length of at least 25 bonds. Liquid crystal compositions are disclosed that include such mesogen compounds, and optical elements that include such mesogen compounds.