ed divalent aromatic group or heterocyclic group; Ar30 and Ar31 are each independently a substituted or unsubstituted aromatic group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted fused polycyclic aromatic group, or a substituted or unsubstituted fused heteropolycyclic group, or Ar30 and Ar31 can be joined to form a ring; and x is an integer of 1 to 10.