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 cycloaddition reactions increasing the excited state of individual chromophores. The fluorescent responses of the tetracenelinked PPEs, however, showed markedly different behavior: (i) an initial increase in fluorescence intensity and fluorescence lifetime of the side-chain tetracenes upon exposure to 1 O 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.

This paper describes conjugated polymers with 2,5diarylfuran moieties as nonconjugated pendants that respond to singlet oxygen ( 1 O 2 ) by fluorescence quenching. By oxidizing the diarylfurans to more electron-poor moieties such as enol esters, singlet oxygen causes poly(fluorene-co-phenylene) conjugated backbones to donate excited electrons to the oxidized pendants, resulting in quenching of up to 93% of the initial fluorescence of the polymer, while an analogous furan-substituted poly(phenylene−ethynylene) showed no quenching upon furan− 1 O 2 reaction. All furan derivatives reacted rapidly with 1 O 2 (k = 10 7 −10 8 M −1 s −1 ), with more electron-poor furans reacting more slowly, but yielding more efficient fluorescence quenching, than less electron-poor furans.

Although acenes with more than three fused rings can both fluoresce efficiently and react with singlet oxygen ( 1 O 2 ) rapidly, their hydrophobic nature presents a challenge to their use in aqueous environments. Herein we report a series of fluorescent, water-soluble random copolymers that each comprise (oligoethylene glycol) methacrylate (OEGMA) and one of several diarylacene methacrylates, including a tetracene methacrylate and a tetraceneothiophene methacrylate. Exposure to 1 O 2 in water oxidizes the pendant acenes, resulting in diminution of their fluorescence intensities. The observed rate of oxidation of the tetracene-containing polymers compares favorably with a commercial 1 O 2 -sensitive dye. Polymers that also include energy-donating coumarin side chains show ratiometric fluorescence changes in response to 1 O 2 .

This account describes progress in the author's laboratory in the area of new fluorescent polymers that respond to the reactive oxygen species singlet oxygen ( 1 O 2 ). Key to the development of these materials are the [4+2] cycloaddition reactions between singlet oxygen and dienes such as acenes and furans. When covalently bound to conjugated polymer backbones, cycloadditions of these dienes with singlet oxygen can yield dramatic changes in the wavelength and intensity of luminescence: three such examples are given here. The account also summarizes our work to understand how changing the chemical structures of acenes affects reactivity with singlet oxygen as well as the cycloreversion of the resulting endoperoxides.

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