Two-Dimensional, Acene-Containing Conjugated Polymers That Show Ratiometric Fluorescent Response to Singlet Oxygen

This paper describes two-dimensional conjugated poly(phenylene-ethynylene)s (PPEs) linked to singlet oxygen-reactive diethynyltetracene units through phenylene ethynylene (PE) bridges that are conjugated to the polymer backbones. Successive Sonogashira coupling reactions enabled the preparation of the tetracene-containing PE pendants, the linking of the pendants to the monomer unit, and the polymerization reactions. Small molecule models of the polymers showed ratiometric responses of fluorescence upon exposure to photogenerated singlet oxygen due to cyclo-addition reactions increasing the excited state of individual chromophores. The fluorescent responses of the tetracene-linked PPEs, however, showed markedly different behavior: (i) an initial increase in fluorescence intensity and fluorescence lifetime of the side-chain tetracenes upon exposure to O-1(2) indicated an analyte-induced slowing of self-quenching due to high local acene concentration, and (ii) ratiometric blue-shifted response did not occur until approximately 75% of pendant acenes were oxidized, highlighting the potential utility of analyte-induced removal of traps in light-harvesting fluorescent materials.