Patent ID: 8435422

Claim:
A compound represented by formula (1): wherein R 1 and R 2 are each independently hydrogen, alkyl having 1 to 10 carbons, alkenyl having 2 to 10 carbons, alkoxy having 1 to 9 carbons, alkoxyalkyl having 2 to 9 carbons or alkenyloxy having 2 to 9 carbons; the ring A 1 , the ring A 2 and the ring A 3 are each independently 1,4-cyclohexylene, 1,4-cyclohexenylene, 1,4-phenylene or 2,3-difluoro-1,4-phenylene; when one of the ring A 1 , the ring A 2 and the ring A 3 is 1,4-phenylene or 2,3-difluoro-1,4-phenylene, the other two are 1,4-cyclohexylene or 1,4-cyclohexenylene; and Z 1 is a single bond, —(CH 2 ) 2 —, —CH 2 O—, —OCH 2 —, —COO— or —OCO—.