. . "To be more specific, the present invention provides, in one aspect, an organic compound shown by the following formula (1): ##STR3## wherein R1 is a hydrogen atom, an alkyl group or a halogen atom, and R2 is X--Ar1 ; X is NH, O or S, and Ar1 is a substituted or unsubstituted aromatic ring having a partial structure represented by formula (2): ##STR4## or a substituted or unsubstituted heterocyclic" . . . . .