Fig. 4. (A) Photoluminescence (PL) intensity and (B) absolute fluorescence quantum yields of PIP–TPE in pH aqueous buffer solutions (λex = 360 nm), inset: photographs of PIP–TPE in pH buffer solutions taken under illumination of a UV lamp at 365 nm; (C) the absolute fluorescence quantum yields of PIP–TPE in different acidic buffer solutions at various viscosities (λex = 360 nm), inset: photographs of PIP–TPE in pH 5.59 solution at a viscosity of 32.46 cP and in pH 5.35 solution at a viscosity of 7.94 cP taken under illumination of a UV lamp at 365 nm; (D) the normalized PL intensities of PIP–TPE in acidic buffer solutions of different viscosities (λex = 360 nm), and protonated PIP–TPE in a thin film (λex = 360 nm) and in THF (λex = 300 nm). All of the data for solutions in 0.8 × 10–5 M were collected at 25 °C.
