Water-Soluble Conjugated Polymers for Amplification of One- and Two-photon Properties of Photosensitizers

Two new water-soluble polyfluorene-based conjugated polymers have been designed and synthesized to act as two-photon light harvesting complexes to amplify the two-photon property of photosensitizers and organic dyes through fluorescence resonance energy transfer (FRET). The two-photon absorption cross sections of the conjugated polymers at 800 nm have been significantly improved by inserting ethynylene and vinylene groups as the bridges, which extend the conjugation length and electron delocalization. By using these conjugated polymers as two-photon light harvesting complexes, the two-photon excitation emission of the photosensitizer, Rose Bengal, was found to be significantly enhanced (by up to 85 fold) through FRET. These studies are expected to provide insight on designing systems with further improved performance for potential applications in two-photon photodynamic therapy, sensing, and imaging.