A Perspective Looking Backward and Forward on the 25th Anniversary of Conjugated Polyelectrolytes.

Conjugated polyelectrolytes are π-conjugated polymers that contain ionic charged groups such as sulfonate (R-SO 3 - ), carboxylate (R-COO - ), or ammonium (R-NR 3 + ) combined with a π-conjugated backbone. This perspective provides a summary review of the key developments in the field, starting from the first reports of their synthesis and properties to application-focused developments. The applications include optical sensors for molecular and biomolecular targets, organic electronic applications, and specific biological applications including cellular imaging and photodynamic therapy. This perspective concludes with a discussion of where the field of conjugated polyelectrolytes is expected to lead in the coming years.