Mono-hydroxylated perylene diimide derivative radical anion (PDI2•−) was synthesized in the presence of Potassium carbonate, dimethylformamide with trace H2O. PDI2•− and PDI2 can convert to each other by regulating pH value and solvents. Furthermore, the PDI2•− can be applied in colorimetric chemodosimeter for the rapid detection of some heavy metal ion, and show high sensitivity for Fe3+. The limits of detection of Fe3+ was 1.38 ppm and response time of 1 min.