Specific examples of R1 to R8 are described below. [0053] Specific examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. [0054] Specific examples of the substituted or unsubstituted alkyl group include a linear, branched or cyclic alkyl group, an alkoxyalkyl group, an alkoxyalkoxyalkyl group, an alkoxyalkoxyalkoxyalkyl group, an alkoxycarbonylalk