. "xy group (preferably containing 2 to 7 carbon atoms). [0263] As a substituent of the alkyl group, a halogen atom, particularly a fluorine atom, is preferred. [0264] Ar may be bonded with at least either Y3 or Y4 to form a ring, or Ar may be bonded with R6 to form a ring. [0265] In such cases, the group formed by combining Ar with at least eith" . . .