a compound is represented by the following formula : in the formula , x is a chalcogen atom . z is carbon or an aromatic ring structure having at least one sulfur , at least one oxygen , or at least one nitrogen in an aromatic ring to which a substituent is attached . n is an integer of 1 to 3 . r 1 and r 2 are independently selected from a hydrogen atom , a halogen atom , a straight , branched , or cyclic alkyl group , a straight , branched , or cyclic alkoxy group , and a substituted or unsubstituted aryl group .