Patent ID: 8580142

Claim:
A compound represented by formula (a): wherein Ra and Rb are each independently hydrogen, alkyl having 1 to 12 carbons, alkenyl having 2 to 12 carbons, alkoxy having 1 to 11 carbons, alkoxyalkyl having 2 to 11 carbons, or alkenyloxy having 2 to 11 carbons, and in these alkyl, alkenyl, alkoxy, alkoxyalkyl, and alkenyloxy, arbitrary hydrogen may be replaced by fluorine; ring A 1 , ring A 2 , ring A 3 , and ring A 4 are each independently 1,4-cyclohexylene, 1,4-cyclohexenylene, tetrahydropyran-2,5-diyl, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, or 1,2,3,4-tetrahydronaphthalene-2,6-diyl; Z 1 and Z 2 are each independently a single bond, —(CH 2 ) 2 —, —(CH 2 ) 4 —, —CH═CH—, —C≡C—, —CH 2 O—, —OCH 2 —, —COO—, —OCO—, —CF 2 O—, or —OCF 2 —; W is —CH 2 —, —CO—, or —CF 2 —; and m and n are each independently 0, 1, or 2, and the sum of m and n is 1 or 2, provided that when the sum of m and n is 1, W is —CH 2 — or —CO—; when m=1 and n=0, ring A 3 is 1,4-cyclohexylene; when ring A 2 is 3-fluoro-1,4-phenylene, W is —CH 2 —.