A water-soluble sunlight erasable ink based on [4 + 4] cycloaddition of 9-substituted anthracene

Over the past few decades, global paper consumption has continued to increase. The growing demand for paper has aggravated the negative impact on the environment. Therefore, the development of an erasable ink or rewritable paper seems to be an ideal way to alleviate this crisis. In this work, a hydrophilic anthracene derivative with nucleophilic substitution at position 9 was designed and synthesized. Such an anthracene derivative could disperse in aqueous solution and dimerize fast under irradiation of UV or visible light, accompanied by fluorescence quenching. Its aqueous solution could be used as a novel ink to be written on conventional paper, of which the handwriting was only visible under ultraviolet light. When exposed to sunlight, the handwriting would gradually disappear and not reappear after irradiating with ultraviolet light or heating. Therefore, it can be used as an erasable ink for applications in data confidentiality or paper reuse.