| As stimuli-responsive functional molecules, molecular switches have a greatapplication prospect in the field of material, chemical and biological medicine and soon. Thus, they are still a research hot spot for scientists. Among them, the spiropyranmolecular switch is the most classic one in the type of organic molecular switches,due to great difference of molecular configuration, volume, change of dipole,especially its large absorption wavelength, accompanied by obvious color changeduring its reversible isomerization. With those unique properties, it should havepotential applications prospect in many aspects. However, due to their characteristics,spiropyran molecular switches existes many problems, such as the slow responsespeed, easy to degradation, and poor fatigue resistance, and so on. In recent years,some new type of molecular switches with better performance (such as oxazines andoxazolidines), have become the more popular research objects. The prevailingcolour-switching stimuli for these molecules are mainly UV/Vis and acid/base,which lead to problems, such as molecular degradation, potential safety issues andenvironmental hazards. These problems limit greatly their practical applications.Therefore, based on new type of molecular switches with better performance, todevelop more green and environmental friendly ways for their reversiblering-opening and ring-closing, and further to expand their applications inenvironmental monitoring and green display, has very important theoretical andpractical significance.In the second chapter, we studied the reversibly switching ofindolino[2,1-b]oxazolidine molecular switches between ring-open forms (OFs) and ring-closed forms (CFs) via introduction or removal of carbon dioxide (CO2), andapplied them in CO2capture and visual monitoring. First of all, we studied thesubstituent effect on stimuli-responsive speed and color for CO2triggeredisomerization of indolino[2,1-b]oxazolidines. Then, the mechanism of CO2triggeredring-opening/closing was researched in details and proved by UV-Vis absorptionspectrum, mass spectrometry, in-situ one-dimensional or two-dimensional nuclearmagnetic resonance (NMR) technology, especially the carbon diffusion orderedspectroscopy. It is proved that the CO2triggered ring-opening/closing ofindolino[2,1-b]oxazolidines is through forming/disconnect of the dynamic covalentbond of carbonate between CF and the CO2. Based on this mechanism, we showedthe applications of indolino[2,1-b]oxazolidines in reversible capture and release ofCO2with the low (or zero) energy consumption. This dynamic covalent CO2capturemethod provides a new way for developing more energy-free method of reversiblecapture and release CO2. Based on their obvious color change with CO2trigger, wefurther applied indolino[2,1-b]oxazolidines in visual monitoring of CO2. Thismonitoring method didn‘t require any additional equipment but naked eyes, so it‘sespecially suitable for remote areas or closed workplaces.In the third chapter, we studied the isomerization of indolino[2,1-b]oxazolidinesbetween CFs and OFs with the stimulation of water (called hydrochromism), anddiscussed its mechanism in detail. Through UV-Vis absorption spectroscopy andNMR spectroscopy, we proved that water could work as a stimulus similar tolight/heat or acid/base, to reversibly and controllably regulated ring-opening/closingof indolino[2,1-b]oxazolidines. Then, the effects of solution concentration, watercontent and the organic solvents on the hyrochromism ofindolino[2,1-b]oxazolidines were investigated. Finally, we discussed and explainedthe hydrochromic mechanism with solvation theory and thermodynamic equilibrium theory, respectively. The solvent-dependence properties of hydrochromism, makeindolino[2,1-b]oxazolidines have the potential applications as a new class ofsolvatochromic dyes for define of solvent polarity. The detailed mechanism study forhydrochromism of indolino[2,1-b]oxazolidines also laid a solid theoretical basis forfurther development of their applications.In the fourth chapter, based on the hydrochromic phenomenon discussed in thethird chapter, we selected the appropriate indolino[2,1-b]oxazolidines ashydrochromic dyes, and applied them in hydrochromic rewritable materials, and putforward water-jet printing technology (printing with water only instead of ink) forthe first time. We ingeniously used multiple functions and roles of polyethyleneglycol (PEG) to overcome a series of problems in loading hydrochromic dyes ontothe solid substrate, and successfully obtained hydrochromic rewritable paper.Combining with the existing ink-jet printing technology, we achieved water-jetprinting. The effects of solution concentration, solvents, dosage and molecularweight of PEG and hydrating additives on quality of prepared rewritable paper wereinvestigated and optimized. The water-jet prints current can keep22hours, and eachrewritable paper can be used more than50times. Different colours of water-jet printscould be achieved using suitable hydrochromic dyes. The results of cytotoxicity testand urgent drug experiments on animals proved that the hydrochromic dyes we usedhere were within low toxicity. According to a rough estimation, the cost per print ofthe rewritable paper would be approximately one percent of the normal ink-jet print.Although the retention time of the prints so far was not long enough for keepingrecords, this water-jet rewritable printing is pointing a very good direction on greenlife, and will inspire further development of better rewritable media for globalsustainable growth.In conclusion, based on dynamic covalent and non covalent interaction respectively, we developed two new stimuli for switching ofindolino[2,1-b]oxazolidines, that is, carbon dioxide and water. And with theuniqueness of the two new stimuli, we expanded the applications of molecularswitches to environmental monitoring and resource recycling. |
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