Preparation Of Layered Double Hydroxide-spiropyran Composited Film Materials And Their Optical And Electric Stimulated Responses

Intelligent response materials, especially the light-triggered systems with changeable structure and function have attracted growing interest, which show broad applications in the fields of photochromic, responsive sensor and photovoltaic conversion. Spiropyran (SP), by virtue of the good response efficiency and open-ring/closed-ring variation, is regarded as a promising molecule in this area. Recently, the development on effective immobilization and decoration of SP compounds so as to obtain multifunctional stimuli-responsive materials and devices is highly necessary and remians a challenge.Layered double hydroxides (LDHs) have been recognized as a representative two-dimension laminar inorganic material, with a facile tunability in both host layer and interlayer guest. LDHs have been widely studied as a model system in intercalation chemistry and extensively explored as functional materials. In recent years, LDHs have been employed as building block for the fabrication of solid-state functional devices via layer-by-layer(LBL) technique, spinning coating or electrochemical deposition. In this dissertation, a series of optical and electric intelligent response unltrathin films(UTFs) have been prepared by using LDHs as the rigid laminate and encapsulated SP micelle as the responsive unit. The fluorescence of SP is enhanced significantly based on the package of amphiphilic micelles block copolymer; the fluorescence responsive unit is immobilized in the interalyer region of LDHs matrix and dispersed orderly in the vertical direction of the UTFs. The resulting functional UTFs avoid the influence of solvent effect,improve the stability of SP, which show potential applications in display,sensors, and optoelectronic devices. The main contents are described as follows:1. Preparation of LDHs/spiropyran UTFs and investigation on their light-triggered switch performanceSP was encapsulated within Poly (tert-butyl acrylateco-ethyl acrylate-co-methacrylic acid) (denoted as PTBEM) micelle. The hydrophobic terminal combining with SP is located in the micelle core, which gives negative (SP@PTBEM) micelle with largely enhanced fluorescence intensity and quantum yield. Subsequently, the solid UTF device was obtained via LBL self-assembly technique by using the negatively-charged micelle and positively-charged LDHs. The resulting UTF undergoes a structural transformation from nonfluorescent closed-ring SP to red-fluorescent open-ring merocyanine (MC) triggered by UV, and subsequently reverts back to SP by visible light. Compared with the liquid switch, this UTF exhibits a relatively uniform and smooth surface without the aggregation of SP. The switching time can be reduced to 15 s by using a high-pressure mercury ultraviolet lamp (8 W), which can be potentially used in ultrafast light-triggered switch.Based on the single photo-responsive switch, a photo/pH dual-stimuli-responsive fluorescent UTF switch was prepared by further introducing a pH-responsive species (riboflavin, Rf). The characteristic of SP is retained in this system, and a photoluminescence quenching of Rf can be caused by ionization of the imido group in the alkaline environment. The UTF composed by LDHs laminate and SP/Rf species shows green fluorescence with closed-ring SP and unionized Rf; then turns to yellow-fluorescence because of a mixture of red-fluorescence MC and green-fluorescence Rf when a UV light is introduced; a red-fluorescence is displayed under the stimulation of both UV and alkaline atmosphere, as a result of the photoluminescence quenching of Rf and open-ring MC. This UTF realizes a three-state dynamic fluorescence by alternative UV/Vis and pH stimulation. It is anticipated that the solid UTF switch can be potentially used in multifunctional response and visual detection.2. Fabrication of multi-dimensional fluorescence resonance energy transfer (FRET) systems and investigation on their FRET efficiencyThe fluorescence donor-acceptor counterparts were encapsulated into the PTBEM micelle simultaneously based on the the insolubility of both donor and acceptor, to achieve an intra-micelle OD FRET. The distance between donor and acceptor in the micelle is 0.86-2.35 nm, which is proved by SEM and theoretical simulation study. At the same time, 2D interlayer FRET was built by assembling negatively-charged donor-acceptor micelle with positively-charged LDHs nanosheets. The distance between two adjacent layers is ?9.8 nm confirmed by XRD. In this work, a multi-dimensional(0D+2D) FRET system is designed and fabricated by orderly assembly of OD dye@micelles and 2D ultrathin LDH nanosheets. As revelaed by time-resolved fluorescence, the lifetime of donor decays sharply from 23 ns to 6.0 n after FRET. In addition, obvious increases in the fluorescence lifetime(from 1.97 to 3.09 ns) and quantum yield (from 2.69% to 5.62%) of the receptor are obtained, which shows an efficient transmission of fluorescence energy. Moreover, the multi-dimensional FRET system exhibits a higher FRET efficiency (81.73%) than that of the single-dimensional FRET (21.58%)system. The enhanced efficiency can be attributed to the compression of micelle by rigid LDHs nanosheets, and the binding effect of LDHs between the donor and acceptor is prosposed as another reason. This fabrication method based on assembly of OD micelles with 2D layered material can be extended to other FRET systems.3. Fabrication of LDHs-spiropyran UTF electrode and investigation on its electrochromism and electrochemiluminescence (ECL)performanceBased on the tunability of LDHs host layer, a LDHs-spiropyran UTF electrode was prepared via the assembly of SP and electroconductive Co-Al LDHs. The open-ring reaction of SP in this UTF electrode can be triggered at a voltage of 1.5 V with remarkable changes in structure and UV-vis absorption.The absorption of ring-open MC at 600 nm changes sensitively with stimulation of positive and negative voltages; the surface roughness of UTF after electrochemistry-triggered becomes larger compared with the initial UTF due to the bigger molecular size of MC. Moreover, the UTF electrode shows a stable ECL signal, which decreases gradually along with the increase of temperature. Once Zn2+ is introduces in solution to coordinate with the ring-open MC, the quenching of ECL signal is observed. This work realizes the electrochemistry-triggered isomerization of SP and exploits the application of SP in ECL response, which can be potentially used in electrochemical sensors and trace elements detection.