Ester compounds, liquid crystal compositions and liquid crystal display devices

An ester compound expressed by the general formula (1)

• wherein R1represents hydrogen atom, cyano group, nitro group, amino group, a halogen atom, a straight chain or branched alkyl group having 1 to 20 carbon atoms, or a straight chain or branched alkenyl group having 2 to 20 carbon atoms;
• one or more hydrogen atoms in these alkyl group and alkenyl group may be replaced by halogen atoms;
• one or more —CH2— in these alkyl group and alkenyl group may be replaced by oxygen atoms or sulfur atoms, but there is no case where oxygen atoms are adjacent;
• and one or more carbon atoms in these alkyl group and alkenyl group may be replaced by silicon atoms;
• A1 to A5 each independently represent 1,4-cyclohexylene, 1,4-phenylene, 1-cyclohexene-1,4-diyl, 3-cyclohexene-1,4-diyl, 1-sila-1,4-cyclohexylene, or 4-sila-1,4-cyclohexylene;
• one or more —CH2— in the 1,4-cyclohexylene, 1-cyclohexene-1,4-diyl, and 3-cyclohexene-1,4-diyl may each independently be replaced by oxygen atoms, sulfur atoms, —CO—, —CS—, SiH2—, —NH—, —CF2—, or —CFH—, but there is no case where oxygen atoms are adjacent;
• hydrogen atoms which bond to carbon atoms at position 2 and position 3, respectively, in the 1-cyclohexene-1,4-diyl or 3-cyclohexene-1,4-diyl may each independently be replaced by fluorine atoms;
• one or more hydrogen atoms in the 1,4-phenylene may each independently be replaced by halogen atoms, halogenated alkyl groups having 1 to 3 carbon atoms, methyl groups, cyano groups, or nitro groups;
• and one or more —CH═ in the 1,4-phenylene may each independently be replaced by nitrogen atoms;
• bonding groups Za to Zd each independently represent single bond, —CH2—, —O—, —C≡C—, —COO—, —OCO—, or an alkylene group or alkenylene group having 2 to 4 carbon atoms;
• one or more hydrogen atoms in these groups may be replaced by halogen atoms;
• and —CH2— in these groups may each independently be replaced by oxygen atom, sulfur atom, —CS—, —NH—, —CF2—, or —CFH—, but there is no case where oxygen atoms are adjacent;
• bonding group Ze represents single bond, an alkylene group or alkenylene group having 1 to 10 carbon atoms;
• and —CH2— in these groups may each independently be replaced by, oxygen atom, sulfur atom, —CF2—, —CFH—, —CH═CH—, —CF═CF—, —CF═CH—, or —C≡C—, but there is no case where oxygen atoms are adjacent;
• n1 to n3 are each independently 0 or 1, but n1≦n2≦n3;
• Y1 and Y2 each independently represent oxygen atom or sulfur atom;
• R2 represents a halogen atom, a straight chain alkyl group having 1 to 20 carbon atoms, or straight chain alkenyl group having 2 to 20 carbon atoms, one or more hydrogen atoms in these alkyl group and alkenyl group are replaced by halogen atoms;
• one or more —CH2— in these groups may be replaced by oxygen atoms or sulfur atoms, but there is no case where oxygen atoms are adjacent;
• and one or more carbon atoms in these groups may be replaced by silicon atoms;
• provided that when A5 represents unsubstituted 1,4-phenylene in this compound, then Zd is single bond, Ze is single bond or an alkylene group having 1 to 10 carbon atoms in which alkylene group —CH2— may independently be replaced by oxygen atom, sulfur atom, —CF2—, —CFH—, —CH═CH—, —CF═CF—, —CF═CH—, or —C≡C—, but there is no case where oxygen atoms are adjacent, and A4 is not 1,4-phenylene;
• and
• each atom which constitutes this compound may be replaced by its isotope.