Provided are (1) a terpyridine monomer that has a strong ability to coordinate with metal atoms, and (2) a polymer material that can be readily switched between a colored state and a colorless state by controlling the electrical potential applied to it and that can be processed.A bis-terpyridine monomer of a first invention comprises a first terpyridyl substituent (A), a second terpyridyl substituent (B), and a spacer that contains at least one benzene ring and links the substituents (A) and (B).A polymer material of a second invention comprises a bis-terpyridine derivative derived from the monomer according to the first invention, a metal ion and a counter anion, or comprise first to Nth bis-terpyridine derivatives (N is an integer of 2 or greater), first to Nth metal ions (N is an integer of 2 or greater) and first to Nth counter anions (N is an integer of 2 or greater).