Homologous series of 4"-nitro- and 4"-cyano-derivatives of 1-(4’-alkoxyphenylamino)-3-phenyl-1-propen-3-ones and a structurally similar series of 1-(4’-alkoxyphenylamino)-3-(4"-pyridyl-N-oxide)-1-propen-3-ones were synthesized and studied by DSC and optical methods. The compounds behave typically for strongly polar mesogens : the smectic A(d) phase exists above a critical chain length and the reentrant nematic phase is observed in the vicinity of the critical double point. For pyridyl N-oxides, a second-order SmA(d) - SmCd phase transition line is observed.