Multiple organic solvent soluble lignin-based macromolecular fluorescent probes for the detection of 4-nitrophenol

Lignin is a kind of natural polymer with high yield, low cost, and easy availability. It is necessary to expand the application range of lignin and reduce the waste of lignin resources. In this work, boron dipyrromethene (BODIPY) with iodine (BO-I) was prepared. Secondly, BODIPY fluorophore with an aldehyde group (BO-CHO) and BODIPY fluorophore with two iodide groups (I-BO-I) were prepared by Vilsmeier-Haack reaction and Iodination reaction based on BO-I. Subsequently, the dealkalized lignin (DAL) with carbon-carbon double bonds (DAL-O-1) and the dealkalized lignin with acetylenic bonds (DAL-O-2) were modified by Williamson ether synthesis reaction. Finally, a lignin-based fluorescent probe (BO-DAL-1) with carbon-carbon double bonds (C--C) and another lignin-based fluorescent probe (BO-DAL-2) with acetylenic bonds (C---C) were prepared by Heck reaction and Sonogashira coupling reaction. In this article, a simple and high-yield synthesis method was used to prepare the lignin-based fluorescent probes. The modified DAL was introduced into BODIPY by design, and lignin-based fluorescent probes were obtained. BO-DAL-1 and BO-DAL-2 could be easily dissolved in a variety of organic solvents (DCM, THF, EtOH, DMF, and DMSO). Moreover, the as-prepared lignin-based fluorescent probes can recognize 4-nitrophenol (4-NP) with high selectivity and sensitivity. The limit of detection (LOD) reaches 0.13 mu M. At the same time, the fluorescence intensity of lignin-based fluorescent probes can be maintained in the solutions with different pH (pH= 2-11). This work provides us with a facile method to enlarge the application scope of lignin.