Rewritable paper based on switchable molecules has attracted great attention in both academic research and marketplace. However, most available switchable dyes have single switchable color state only, which cannot meet the longawaited multicolor reversible displays. Herein, through simple introduction of phenolic hydroxyl group, we develop a series of new oxazolidines with one switch unit, which could reversibly display two different as well as their mix-gradient colors by treating with water and mild acid, respectively, both in solution and solid substrate. The structures and mechanism for the formation of two colors had been studied in detail via UV−vis/NMR spectroscopy, skillfully designing contrast molecules, and kinetics experiments. This multiple switchable colors of the dyes have been further applied to construct a rewritable paper for ink-free printing with multi/gradient-color display.

A new absorption/fluorescence dual-mode hydrochromic dye and its latent applications in a water-jet rewritable paper and encrypting information have been developed.

Reversible multicolor displays on solid media created from single-molecule pigments are a long-awaited goal. Herein, a new and simple molecular dyad, which can undergo switchable cyan (C), magenta (M), and yellow (Y) color changes in both solution and the solid state upon exposure to light, water/acid, and nucleophiles, has been designed and synthesized. The stimuli used herein can be applied independent of each other, which is beneficial for color changes without mutual interference. For comparison, mixtures of the two molecular switching motifs that form the basis of the dyad were also studied. The dyad greatly outperforms the corresponding mixed system with respect to reversible color switching on the paper substrate. Its potential for full-color rewritable paper with excellent reversibility has been demonstrated. Legible multicolor prints, that is, high color contrast and resolution, good dispersion, and excellent reversibility, were achieved by using common water-jet and light-based printers. This work provides a very promising approach for the further development of full-color switchable molecules, materials, and displays.

Ring-closing of ROF+X− generated biomimetic inverse proton gradient was successfully achieved via varying microenvironment for improved performance of water-jet rewritable paper.