Examples of the substituent of the above-mentioned aryl group represented by Ar2 and Ar7 include a halogen atom such as fluorine atom, chlorine atom, bromine atom and iodine atom, cyano group, nitro group, an alkyl group which may have a substituent, an alkoxyl group which may have a substituent, and an amino group represented by the following formula (X): ##STR22## in which R18 and R19 each is an