A copolymer having two or more repeating units selected from the group consisting of arylene groups, divalent heterocyclic groups and divalent aromatic amine groups wherein the copolymer has, on at least one of molecular chain ends, a monovalent heterocyclic group, a monovalent group derived from a heterocyclic group coordinated metal complex, and an aromatic end group selected from aryl groups having a formula weight of 90 or more, and the copolymer shows fluorescence in the solid state and has a polystyrene-reduced weight-average molecular weight of 103 to 108.