A chiral, tilted, smectic liquid crystal phase comprising a mixture of at least two compounds, wherein at least one compound is an achiral fluorinated biphenyldiole compound of formula I ##STR1## whereinR.sup.1 and R.sup.2 are each independently alkoxy or alkanoyloxy with 1 to 15 C atoms, ##STR2## denotes a 4,4-phenylene group optionally substituted by up to four F atoms, and is 1.