Study On Novel Photochromic Dithienylethene System Based On Benzo[b]Thiophene-1,1-Dioxide Unit As Central Ethene Bridge

Photochromism is an electromagnetic radiation induced reversible transformation of a chemical species (A) between two states (A and B) with different distinguishable absorption spectra. It is a specific kind of photo-chemical reactions with reversibility. During the photochromic reaction, the changes in chemical structures to two isomers with different physic-chemical properties, which represent the "0" or "1" binary digital codes. Therefore, photochromic materials can be expected to the application in photonic devices, such as optical information storage and molecular logic gates and so on. Moreover, the typical photochromic reaction can also be utilized to modulate the microenviorment properties making them become increasing interest in the field of photo-driven molecular devices, fluorescent modulation and biochemical systems.In order to develop novel photochromic systems with achieving practical applications, dithienylethene derivatives based on benzo[6]thiophene-1,1-dioxide unit as central ethene bridge were put forward, with focus on excellent thermal irreversibility and outstanding fatigue resistance. By the introduction of the specific imidazole and pyridine units, multi-addressable photochromic systems responding to chemical ions, protons and light have been successfully realized, especially for the fields such as complicated molecular logic gates, self-assemble system and fluorescence modulation. The main contents and results are outlined as follows:In introduction, the definitions and main parameters of organic photochromic systems have been given, and the recent progress of diarylethene photochromic materials was reviewed.A series of diarylethenes BTT-1, BTT-2, BTT-3, BTT-4and BTT-5containing benzo[6]thiophene-1,1-dioxide unit as central ethene bridge were designed and synthesized. The π conjunction systems of dithienylethene derivatives can be modulated by tailoring thiophene side chain, resulting in the solution color changed from red (c-BTT-1) to blue (c-BTT-2), deep blue (c-BTT-3), navy blue (c-BTT-4), and until to green (c-BTT-5). Moreover, crystals of BTT-1, BTT-2and BTT-3were obtained by slow evaporation method. As shown in X-ray diffraction, BTT-1adopted an anti-parallel conformation, and the distance between the reactive carbon atoms is3.516A, meeting the preconditions for a molecule undergoing photochromic reaction in crystalline phase, while BTT-2and BTT-3adopted a parallel conformation, resulting in no photochromic reactions in crystal state. A photochromic bisthienylethene derivative (BIT) containing two imidazole units was synthesized and fully characterized. The fluorescence of it can be modulated through the typical photochromic reactions. When triggered by chemical ions (Ag+), protons and light, BIT can behave as an absorbance switch, leading to a multi-addressable system. Moreover, BIT exhibited sequence-dependent responses via efficient interaction of the specific imidazole unit with protons and Ag+. An INHIBIT logic gate and a keypad lock with three inputs (H+, Ag+and365nm light) were constructed with the unimolecular platform by employing absorption mode (610nm) as outputs on the basis of appropriate combination of chemical and photonic stimuli.The photochromic terarylene (BTO) containing benzo[b]thiophene-1,1-dioxide unit as central ethene bridge was synthesized and characterized, exhibiting good thermal stability and fatigue resistance both in solution and bulky crystals. When triggered by chemical ions, protons and light, BTO can behave as an absorbance and fluorescence switch, leading to a multi-addressable system. The titration of the Job plot indicates that BTO forms a1:1and2:1complex with Hg2+and Cu2+, repectively. The different color changes of BTO upon adding Cu2+and Hg2+ions arise from the relative binding stoichiometry and the association affinities. Moreover, the conversion yield of BTO can be modulated with chemical ions. Impressively, an increase in conversion yield was observed by adding Hg2+to the solution of BTO, that is, the conversion yield and cyclization quantum yield are increased from77.6%and28.5%(for BTO only) to99.8%and43.1%(BTO-Hg2+), respectively. A series of molecular logic gates such as half-adder, half-subtractor,4-to-2encoder,2-to-4decoder, and1:2demultiplexer were constructed on the unimolecular platform by employing absorption and emission properties at different wavelengths as outputs with the appropriate combination of chemical and photonic stimuli.The first example of quantitative reversible transformation of light-triggered supramolecular hexagons were prepared through coordination-driven self-assembly between dipyridine unit BTO or its closed form c-BTO and the120°or180°di-Pt(Ⅱ) acceptor. Those multi-bisthienylethene hexagons were fully confirmed by1H NMR,31P NMR, element alanalysis, and ESI-TOF-MS. Furthermore, those hexagons possess several merits as follows:(i) precisely controlling shape and size as well as the number of the specific photochromic units,(ii) unprecedentedly achieving quantitative ring closure for all photochromic units in the hexagons due to the coordination induction, and (iii) quantitatively and reversibly interconverting between the ring-open and ring-closed conformation via alternate irradiation with the UV and visible light, respectively.A kind of core-shell structured silica nanoparticles containing diarylethene unit and/or aggregation-induced emission (AIE) characteristic chromophore, named BTO@Np, ED@Np and BTO-ED@Np were developed via the self-assembly of the amphiphilic block copolymer PS-b-PAA, with a narrow size distribution and excellent dispersity in aqueous solution. Moreover, the typical AIE and photochromic phenomenon were observed in those nanoparticles. The fluorescence of the BTO-ED@Np can be reversibly modulated by the specific photochromic reaction of BTO. The novel photochromic material BTO-ED with aggregation-induced emission (AIE) characteristic was designed and synthesized. Its AIE effects were fully studied with absorption and fluorescence spectra. Moreover, an interesting AIE induced specific gated photochromism phenomenon was observed.