A bis(2-aryl-5-pyridyl) compound having formula (1) or a salt thereof: wherein A is a substituted or unsubstituted aromatic hydrocarbon group, and X is a substituent having one of the following formulas (2) to (4): wherein, in formula (2), R1 is a hydrogen atom or a di(lower alkyl)amino(lower alkyl) group, and m is an integer of 1 or 2; in formula (3), Y1 and Y2 each is a nitrogen atom or a CH group, and n is 0 or an integer of 1 to 6; in formula (4), R2 and R3 each is a hydrogen atom or a lower alkyl group, Z represents a single bond, a substituted methylene group, a substituted imino group, an oxygen atom or a cycloalkylene group, and p and q each is 0 or an integer of 1 to 6.