A new anionic conjugated polymer containing a fluorene group in the main chain was designed and synthesized from poly(2,7-(9,9'-dihexylfluorene)-5,5'-bibenzimidazole) (PFBI). The polymer showed strong blue emission with high quantum efficiency (0.64) at 450 nm in MeOH and the dramatic quenching effect by Methyl Viologen (MV2+). The fluorescence-quenching effect results from the weak complex formation between an anionic polymer and electron acceptors such as bipyridinium derivatives. The linear Stern-Volmer constant (K-sv) was 3.7x10(5) M-1 for MV2+. The newly synthesized polymer is expected to show the applicability for biological and chemical sensors. (C) 2003 Wiley Periodicals, Inc.