The improvement of lysosome targetability with oligoethyleneoxy chains linked benzo[a]phenoxazine

[Display omitted] •The introduction of oligoethyleneoxy chains improves biocompatibility of probes.•Comparative study of the probes connecting different oligoethyleneoxy groups.•Good biocompatibility of benzo[a]phenoxazine derivatives improves its lysosome targetability. In order to improve lysosome targetability of probes, fluorescent probes based on benzo[a]phenoxazine attaching different length oligoethyleneoxy chains were designed and prepared. Probes 2a–c containing N-pyridineium-3-yl exhibited almost ON-OFF near-infrared emission responses at 697–701 nm from pH 2.8 to 7.2, and the calculated pKa values of 2a–c were 4.90, 4.92 and 5.03 respectively. More importantly, fluorescent imaging experiments indicated that probes 2a–c were all lysosome biomarkers for Ges-1 and HeLa cells, which was because the introduction of oligoethyleneoxy groups improved the biocompatibility of probes, so that the probes 2a–c were better transported to lysosomes via the endocytosis pathway of the cells. Moreover, the probe 2a was selected as a representative, which not only showed good reversibility and selectivity, but used to successfully image lysosomal pH increases induced by chloroquine.