Absorption/Fluorescence Dual-mode Hydrochromic Rhodamine Derivatives

Nowadays,the large demand for paper needs to consume a lot of forest resources,and many papers are abandoned after be used by one time,which will waste a lot of natural resources and produce a lot of solid waste.In such cases,sustainable human development will be affected.As a result,many studies have been carried out in recent years based on the rewritable paper to address or mitigate the massive waste of natural resources.The core of rewritable paper is "smart stimulus responsive material",which can respond to external stimuli and change their color/fluorescence.The water-stimulated rewritable materials have been greatly concerned and studied because of the advantages of green environmental protection,compatibility with existing ink-jet printing technology and so on.Most reported hydrochromic materials have only a single display mode,such as a single visible mode and a single fluorescent mode.There are still few studies on the hydrochromic materials displayed in the visible-fluorescent dual mode.The material combined with visible and fluorescent dual mode will collect strengths of those materials,and will have a broader application prospect.In the first chapter,we introduce the hydrochromic materials developed by various research groups in recent years(single display mode and double display mode),which plays a guiding role in the topic selection of this paper.In addition,reusable materials with other stimulation methods are also introduced,which broadens our vision and provides inspiration for developing more applications of materials.In the second chapter,using NH2-Rh B as parent molecular structure,a series of rhodamine derivatives with different electron-withdrawing/donating sub-substituents on amino group have been designed and synthesized.The effects of the electric properties of the sub-substituents on the hydrochromic ring-open reaction of these molecules as well as the effects of the interactions between the ring-open molecules and water around them on their hydrochromic absorption/fluorescent properties have been studied in detail.The reason why hydrochromic fluorescence of NH2-Rh B quenching was revealed,and a novel dual-mode hydrochromic fluorescent dye(CH3)2-N-Rh B was constructed successfully.Finally,we combined the newly synthesized dual-mode hydrochromic dye with NH2-Rh B,and demonstrated their applications in the fields of dual-mode information display and dual-encryption system.Our work provided new ideas for the development of more kinds of hydrochromic absorption/fluorescence dual-mode dyes with better performance and paved the way for their broader application prospect.In the third chapter,since most methods for finding suitable hydrochromic fluorescent dyes need to redesign and synthetic molecules,we propose a method that takes use of the rhodamine over-protonation phenomenon which can be applied to rhodamine derivatives.We also prepared a hydrochromic fluorescent material based on dual-mode display.We load both dye molecules and strong acids on the paper,and the molecules before adding water are in a colorless and fluorescence-free state because of over-protonation,while after adding water,the concentrated acid is diluted,and the molecules return from the state of over-protonation to the ring-open state with color and fluorescence.At the same time,we can also make the material have two color rendering modes from "on" to "off" or from "off" to "on" by regulating the type of acid.