. "In the formula (II), each of R7 and R8 independently is an alkyl group (e.g., methyl, ethyl, propyl), an alkoxy group (e.g., methoxy, ethoxy), an aryloxy group (e.g., phenoxy, p-chlorophenoxy), a halogen atom (Cl, Br, F), an alkoxycarbonyl group (e.g., ethoxycarbonyl), a carbon halide group (e.g., trifluoromethyl), an alkylthio group (e.g., methylthio, ethylthio, butylthio), an arylthio group (e.g" . . . .