Tolane derivatives and liquid crystalline medium

A tolane compound of the formula I

• wherein
• R1 is an alkenyl group with 2 to 12 C-atoms,
• R2 is H, halogen, CN, or alkyl with 1 to 12 C-atoms, wherein one or more CH2-groups are optionally replaced by —O—, —S—, —CO—, —O—CO—, —CO—O—, —CH═CH— and/or —C≡C—, and/or wherein one or more H-atoms are optionally replaced by halogen,
• L1, L2 and L3 are independently of each other H or F, with the proviso that, if L3=H, then L1 and L2=F.