Unusually high fluorescence quantum yield of a homopolyfluorenylazomethine – towards a universal fluorophore

Abstract

The absolute fluorescence quantum yield (Φ_fl) of a polyfluorenyl azomethine homopolymer was measured as a function of solvent polarity. The solvent induced and temperature dependent fluorescence of the homopolymer were also investigated and they were compared to the corresponding monomer and copolymer. The Φ_fl of the homopolymer was consistent (45–70%), regardless of solvent polarity with Stokes shifts up to 7460 cm⁻¹ in ethanol. In contrast, the Φ_fl of its corresponding monomer decreased from 60% in ethanol to 1% in toluene, whereas a Φ_fl < 5% for its analogous copolymer was measured. Moderate fluorescence yields (Φ_fl ≈ 25%) were also possible in thin film when co-depositing the homopolymer with PMMA. Cryofluorescence was used to probe the excited state deactivation modes. Deactivation by internal conversion was found to compete with fluorescence. The fluorescence deactivation pathways of the homopolymer and its corresponding monomer could be suppressed at 77 K, resulting in fluorescence turn-on. Both fluorophores were found to detect nitroaromatics.