AMPHIPHILIC ALTERNATING CARBAZOLE COPOLYMERS - PHOTOPHYSICAL PROPERTIES OF POLY[N-VINYLCARBAZOLE-ALT-CITRACONIC ACID] IN AQUEOUS-SOLUTION

Amphiphilic polyelectrolytes containing carbazolyl chromophores (a-CzCa) were prepared by hydrolysis of alternating copolymers of N-vinylcarbazole (VCz) and citraconic anhydride and their fluorescence properties were compared with those for alternating copolymers of VCz and maleic acid (a-CzMa) and random copolymers of VCz and methacrylic acid (r-CzMA(x)) in aqueous solution. The fluorescence spectrum of a-CzCa, derived from the anhydride copolymer with the equimolar monomer feed ratio, showed a predominant monomer emission in both organic and aqueous solutions, while the fluorescence intensity changed drastically upon dissociation of carboxyl groups in aqueous solution and had a minimum value at acidic pH which was rather smaller than that for the corresponding random copolymer. The solution behavior showed that a-CzCa had a less hydrophobic character and thus retained a loose form even at low pH. Therefore, the remarkable self-quenching occurring in a-CzCa may be caused primarily by efficient energy migration to very few quenching sites. Quenching experiments gave additional evidence for hydrophilicity of a-CzCa. The fluorescence of a-CzCa at pH 3 was found to be quenched less efficiently by an amphiphilic quencher, bis(2-hydroxyethyl) terephthalate (BHET), compared with the corresponding random copolymer.