Red-Emitting, Acene-Doped Conjugated Polymer Nanoparticles that Respond Ratiometrically to Photogenerated 1O2

Fluorophores that respond to external stimuli on demand have numerous applications in imaging and chemical or biological sensing. In this paper, we describe conjugated polymer nanoparticles (CPNs) that comprise a donor polymer matrix and a red-fluorescent, singlet oxygen-reactive heteroacene dopant (DE-TMT) that display a ratiometric response upon photo-oxidation. This ratiometric response can be tuned by the level of doping of DE-TMT, the identity of the conjugated polymer matrix used, and the blending of two conjugated polymers together to access red-shifted emission wavelengths. We followed a rational design process that combined (i) fundamental understanding of the influence of the chemical structure on luminescence spectra and efficiencies, energy transfer efficiencies, and reactivity and (ii) systematically determining how blending multiple chromophores in nanoparticles influences energy transfer efficiencies and the speed of optical responses to irradiation. Our approach of refining the compositions of these nanoparticles has yielded materials that combine many desirable characteristics for analytical applications—utility in aqueous environments, high quantum yield, emission of red light, and ratiometric luminescent responses. We anticipate that the type of approach described herein can be of use to others in designing CPNs for luminescence applications.