Synthesis And Properties Of Photochromic Functional Materials Containing Fluorescent Moieties

Photochromism is defined as a reversible photo-transformation of a chemical species between two forms (A and B) having different absorption spectra. Each isomer of the photochromic compounds can represent "0" or "1" binary digital code corresponding to "on" and "off" states modulated by UV/Vis irradiation or heat. Therefore, the specifically molecular property of photochromic materials can be applied to photonic devices, such as optical information storage, molecular switch, multicolor-display and photo-driven molecular devices. In order to achieve practical applications, novel photochromic compounds containing fluorescent moieties, such as naphthalimide and benzothiadiazole chromophores were put forward. Two parts are included in this dissertation, that is the synthesis and properties of thermal irreversible bisthienylethenes (BTEs) and thermal reversible naphthopyrans, the main contents are as follows:In charpter one, the recent progress of organic photochromic materials was reviewed. And the emphasis of the review was paid to the structure decorations and potential application prospects of BTEs. Also the categories, synthesis, photochromic mechanism and applications of naphthopyrans were reviewed in detail. At last the target of our research was brought out.In charpter two, a novel BTE photochromic system BTE-NAFc based on ferrocenyl (Fc) and naphthalimide units was developed. The fluorescence of naphthalimide chromophore is efficiently quenched due to PET from Fc unit to naphthalimide moiety. The fluorescence of BTE-NAFc can be well modulated by chemical redox using Fe(CIO4)3as oxidant and LAS as reducing agent, and/or by electrochemical redox with0.8V oxidation and-0.6V reduction potentials, successfully realized fluorescence molecular switches. Interestingly, chemical oxidation and electrochemical redox induced ring-opening of photochromic BTEs was observed. As demonstrated, the incorporated Fc unit in the photochromic system of BTE-NAFc shows several characteristics:PET switch, a two-step selective oxidation process (Fc and thiophene units), fluorescence modulation with redox and photochromism, and a decrease in cyclization quantum yield and PSS conversion yield. Moreover, after oxidation with Fe(C104)3, oxidation state BTE+-NAFc+cannot be converted to its closed formed, showing a specific photochromic "Lock" gate. Based on these meaningful properties, five multi-addressable states (BTE-NAFc, BTE-NAFc+, c-BTE-NAFc, c-BTE-NAFc+ BTE+-NAFc+) and gated photochromism modulated by photo-response and chemical/electrochemical redox was constructed within a unimolecular BTE platform, making a further step towards potential applications in sensing and labeling as well as for data manipulation on the unimolecular level.In chapter three, the solid and quasi-solid state is necessary for practical applications in optoelectronic devices. Polymer with good film-forming properties has aroused a surge of attentions. On the basis of naphthalimide chromophore, a novel photochromic polymer poly(NIPMAM-co-BTE) was synthesized by radical polymerization. Polymer parameters such as number and weight average molecular weight (Mn and Mw) were characterized by Gel chromatography (GPC) method. Photochromic and fluorescence properties of monomer BTE and poly(NIPMAM-co-BTE) in solution and thin film were preliminary investigated.In chapter four, novel BTEs (BTE-O and BTE-NH) based on naphthalic anhydride and naphthalimide moieties as central ethene bridging units were designed and synthesized. Photochromic and fluorescence properties of BTE-O and BTE-NH were preliminary investigated, and chemical shift of different protons at open and closed isomers was studied via1H NMR titration upon photoirradiation. Research shows that both BTE-O and BTE-NH possess characteristic solvatochromism owing to intermolecular charge transfer (ICT) effect. The luminescent wavelength of BTE-O was shifted by153nm to long wavelength from nonpolar cyclohexane to polar acetonitrile, whilst137nm was red-shifted for BTE-NH owing to the relatively weak ICT effect resulted from decreased electro-withdrawing ability of imide moiety.In chapter five, naphthopyran is a kind of very important photochromic compounds, which possess highly photochromic response, rapid thermal bleaching rate and excellent fatigue-resistance, has attracted much attention in recent years. Two novel photochromic naphthopyrans Nip1and Nip2bearing naphthalimide units and reference compound NP have been synthesized and investigated. Owing to the different N-substituted imide group at naphthalimide unit, the thermal bleaching rate of Nip2bearing phenyl on the naphthalimide unit is found to be approximately two times that of Nipl bearing n-butyl, indicating that the photochromic properties can be modulated with introduction of different functional groups on naphthalimide unit. In Nip1and Nip2, the strong electron-withdrawing effect of the imide group incorporated at naphthalimide moiety maintains several merits:i) shifting absorption bands to longer wavelength, ii) beneficial to an enhancement in the ratio of TC(transoid-cis) isomer and an increase in the transformation rate from TT(transoid-trans) to TC with respect to reference compound NP, and iii) resulting in a preferable color bleaching rate and fading absolutely to their colorless state with thermal reversibility. Their optical densities of colored forms are dependent upon the intensity of incident light, ensuring a possible application in manufacture of ophthalmic lenses and smart windows. Moreover, the fluorescence of Nip1and Nip2can be switched On and Off by photo-induced conversion between the closed and open forms.In chapter six, on the research basis of photochromic naphthopyrans mentioned last chapter, benzothiadiazole moieties were innovatively incorporated into naphthopyran systems. BTD series compounds (BTD1、BTD2and BTD3) with two, one and none methoxy groups were synthesized and fully investigated. Research shows that the maximum absorption wavelength of open forms after photoirradiation was red-shifted and the thermal bleaching rate of colored forms was increased along with the increasing methoxy numbers, showing specific substituent effect. Moreover, the absorbance at PSS of BTD series compounds also possessed incident intensity dependent properties.In chapter seven, other works:bisthienylethene TBDD based on benzo[1,2-b:4,5-b’]dithiophene-4,8-dione as central ethene bridging unit was designed and synthesized. TBDD shows no photochromic properties according to preliminary investigated results. Some other unsuccessful works or compounds, including bisthienylethene based on naphthalimide moiety and naphthopyrans based on benzothiadiazole moieties, were summarized.In chapter eight, a concise conclusion about the above works was given.