A water-soluble, ratiometric fluorescent pH probe, L-SRhB, was synthesized via grafting spirolactam Rhodamine B (SRhB) to lignosulfonate (LS). As the ring-opening product of L-SRhB, FL-SRhB was also prepared. The pH-response experiment indicated that L-SRhB showed a rapid response to pH changes from 4.60 to 6.20 with a pK of 5.35, which indicated that L-SRhB has the potential for pH detection of acidic organelle. In addition, the two probes were internalized successfully by living cells through the endocytosis pathway and could distinguish normal cells from cancer cells by different cell staining rates. In addition, L-SRhB showed obvious cytotoxicity to cancer cells, whereas it was nontoxic to normal cells in the same condition. L-SRhB might have potential in cancer therapy. L-SRhB might be a promising ratiometric fluorescent pH sensor and bioimaging dye for the recognition of cancer cells. The results also provided a new perspective to the high-value utilization of lignin.

Lignosulfonates obtained from pulping spent liquor are nontoxic and renewable polymers with excellent dispersibility as disperse dye dispersants. In order to reveal its dispersion mechanism on the dye, the adsorption characteristics of sodium lignosulfonate (NaLS) and sodium naphthalenesulfonic acid formaldehyde (NSF) were investigated using a quartz crystal microbalance with dissipation (QCM-D) and an atomic force microscope (AFM). The results showed that the adsorption of dispersant onto the dye film layer was low and unstable without salt, but the adsorption amount of NaSL or NSF onto dye film was increased significantly with the increase in ionic strength. This indicated that hydrophobic effect was the main interaction between dispersant and dye. The adsorption amounts of both dispersants were decreased with the increase in temperature. NaLS exhibited the better dispersion and improved stability at high temperature than NSF due to higher adsorption amount and the viscoelastic adsorption layer.

Inspired by the p-doped PEDOT:PSS, a traditional anode modifier, we proposed to prepare polydopamine:polystyrenesulfonate (PDA:PSS) via the self-polymerization of dopamine in aqueous PSS initially. However, DA and its semiquinone radical were dispersed by PSS to form DA:PSS successfully. Interestingly, a strong electron spin resonance signal was detected in DA:PSS, suggesting the stable semiquinone radical was formed. More importantly, water-soluble DA:PSS exhibited stable and quasireversible electrochemical oxidation behavior, and excellent filmformation capability. Consequently, as an indium tin oxide (ITO) anode modifier, solution processed DA:PSS film showed hole injection property in organic light emitting diodes. Our results open a new avenue for the design of semiconductor and organic electronic application inspired by the electron transfer of phenol derivatives such as DA. Phenol-based organic electronic material has showed potential and it should be taken into consideration in the future.

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