Preparation Of Photochromic And Hydrochromic Materials And Application In Rewritable Paper

"Paper"has made a great contribution to the development and spread of civilization.Even in today’s"digitization"world,paper still plays a key role in all aspects of office and life,and global paper consumption continues to grow quickly every year.However,the manufacture and use of paper will bring many energy and environmental problems.Nowadays,large amounts of paper are usually discarded after only one use,and the current printed matter is not well deinking and recycled,which has caused huge solid waste and environmental pollution problems.To solve these problems,rewritable technology which can help to reduce paper consumption has been widely reported by researchers.However,there are still some problems to be solved,such as single color change of color-developing materials,poor fatigue resistance of materials,and difficulty in water and black printing.Based on these,we designed and synthesized two types of discoloration materials for rewritable paper.1.The carboxyl spiropyran（SP-COOH）and the molecule 1（Rh-NH₂）are covalently combined by amidation reaction to synthesize a new organic discoloration molecule C with photochromic,halochromic and mechanochromic properties.The molecule C has excellent photochromic and halochromic properties in both solution and solid state,as well as excellent stability and reversible discoloration properties.The film CPMMAF prepared by doping molecule C with polymethyl methacrylate can show a clear pattern after 120 s of ultraviolet radiation.After 100 cycles,the performance will not be weakened.In addition,the rewritable paper CP loaded with molecule C can realize UV light and acid printing.Excellent discoloration properties and fatigue resistance make it a promising candidate in UV printing and rewritable papers.2.Two kinds of hydroresponsive covalent organic frameworks（COF1 and COF2）are designed and synthesized.Both frameworks show good hydrochromic properties and excellent fatigue resistance.The COFs are loaded on the filter paper by vacuum filtration to prepare rewritable papers.This rewritable paper will change its color obviously when it contacts with water,and not fade for at least 10 hours in the daily environment.This properties ensures that the retention of the content on the rewritable paper,and then heating it at 75℃for 7 minutes can erase the contents.It not only has excellent hydrochromic properties,but also has excellent stability and fatigue resistance without obvious fatigues during 20 times of water writing/thermal erasing.In addition,we synthesize COF2 film by interfacial polymerization,and adsorb it on paper,thus obtaining rewritable papers.The film not only adheres to cellulose papers with good adhesion,but also has the same discoloration performance.The system exhibits excellent hydrochromic properties and fatigue resistance,making it a potential application in the field of rewritable paper.