Construction And Characterization Of A Photochromic And Fluorescent Multifunctional Supramolecular System With Electron Transfer Properties

Fluorescent-photochromic functional materials have shown potential applications invarious fields such as optoelectronics, information storage, fluorescent switches, fluorescentsensors and attracted a wide range of research interests. Coupled fluorescent-photochromicmolecular systems based on electron transfer reactions not only have fast responses and highthermal stabilities, but also can avoid tedious organic syntheses. More importantly, theirphotosensitive characteristics can be modulated through the rational design of their hostingframeworks, electron donors and/or electron acceptors as well as luminescent centers. Thisstrategy is able to extend the multi-functionality and applications offluoresecent-photochromic materials. Based on electron-deficient viologen compounds andaimed at controlling photochromic and fluorescent properties via electron transfer reactions,this thesis focuses on the rational design and syntheses of a series of novelfluorescent-photochromic multifunctional materials and the characterizations of theirluminescent, photochromic, electron transfer and energy transfer properties. The specificresearch achieves are listed below:1. HCPBPY(N-(3-carboxyphenyl)-4,4’-bipyridinium chloride) was used as an electronacceptor and H4BTEC(pyromellitic acid) was adopted as an electron donor. Threesupramolecular polymers with dissimilar properties were synthesized under differentconditions. Structural analyses and physicochemical characterizations reveal that the differentvalance states, ratios and arrangements of donors and acceptors and distances between donorsand acceptors result in difference in their fluorescent properties and photoinduced electrontransfer rates. This research exploits the structure-property relationship within electron transfersupramolecular systems and throws light on controlling the intermolecular interactions andstructural arrangement in the molecular level and manipulating their photoactive properties.2. A dual stimuli-responsive coordination polymer was constructed by introducingphotosensitive methyl viologen into a luminescent europium-organic framework with acompact packing mode. Its UV-vis absorption and emission properties are sensitive to bothlight and heat. Upon irradiation or heating, excited electrons can transfer from theelectron-sufficient anionic organic framework to the electron-deficient methyl viologendications, involving a photochromic process. Due to the good energy overlap of the Eu-basedemission and absorption spectrum after excitation, the Eu-based fluorescence was significantlyquenched via resonant energy transfer. Since it not has a spectral response from UV to thevisible region, but also can change its emissive and absorptive properties after light or heatexcitation, this coordination polymer has a significant application perspective inphotosensitive-thermosensitive hybrid materials.3. A series of doped lanthanide-organic framework, [Ln4(BDC)6(CPBPY)(H2O)]·H2O(Ln= La, Eu), are synthesized by hydrothermal reaction with lanthanide acetates, isophthalic acidand HCPBPY. The emissive band of [Ln4(H2O)(BDC)6(CPBPY)]·H2O centers at 517 nm,while [Eu4(H2O)(BDC)6(CPBPY)]·H2O exhibits typical Eu(III)-based f-f transition redemission. Through varying the ratio of La and Eu in the starting materials, luminescentpolymers that emit yellow-green, yellow and orange lights could be obtained. Electron transferreactions can undergo in these compounds upon photo-irradiation to yield CPBPY radical,which shows strong absorption near the 617 nm. The good overlap of the absorption band andthe Eu-based emission band leads to that the red emission suffers more from resonant energytransfer. The chromatic values of the photoluminescence of the complexes change afterirradiation and can be recovered upon heating. Besides, by varying the excitation wavelengthfrom 375 to 345 nm, the chromatic coordinations of the doped compounds shift from the greenzone to the red zone. These luminescent coordination polymers are suitable for ratiometric orcolorimetric fluorescent switch or non-destructive information storage applications.