Of the compounds represented by formula (I), particularly preferable compounds are represented by formula (II) or (III): ##STR3## wherein R1 has the same meaning as defined for formula (I), R0 has the same meaning as R1, and R1 and R0 may be the same or different, provided that when R1 is a hydrogen atom, a halogen atom, or a cyano group, R0 is not a hydrogen atom, a halogen atom, or a cyano group