Assembly And Properties Of Inorganic/Organic Composite Supramolecularlayered Photofuntional Materials:Experimental And Theoretical Study

Recently, the fields of chemical engineering, energy, environment andmaterial science have obtained new ideas from supramolecular science,which pave a new way for designing new types of functional materials.Layered double hydroxides (LDHs) are a class of inorganic lamellarfunctional materials with supramolecular structure. LDH powder systemshave a wide variety of industrial applications in the fields of functionaladditives, biological and medical materials, catalysts as well as absorptionmaterials. The construction of LDHs-based uniform thin films canprovide the basis for development of novel optical/electric devices, butalso can put forward new scientific problems based on supramolecularchemistry and solid chemistry principles.Light is an important energy resource. Photofunctional materials cantransfer, absorb, store and switch the light energy. Recently, the organicπ-conjugated compounds (conjugated polymer, organic small moleculeand metal complex) have been received much attention from both academic and industry fields as a result of their advantageous propertiessuch as high quantum yield, easy processing, low cost and well-definedcolor photoemission. These materials have been used in photo-/electroluminescence, dye laser, polarized emission, optical sensor,stimuli-responsive materials and non-linear optics. Key problems, such asfluorescence quenching, short service lifetime, and relatively poor thermalor optical stability, restrict their optoelectronic application. Therefore,how to enhance the photoemission performance of such photoactivematerials has continued to be a challenge.In this dissertation, based on a supramolecular design perspective andthe problems in organic photofunctional materials, we have put forwardthe construction of new types of photofunctional inorganic/organiccomposite materials by the incorporation of photoactive guest into LDHhost matrix with the aid of exfoliation-assembly andintercalation-assembly methods. The aim of this study is to optimize andenhance the photoemission efficiency and optical properties of organicmaterials. By the use of both experimental and theoretical study, we haveinvestigated the geometry, electronic structure, energy levelcharacteristics, and host-guest interaction of these supramolecularsystems, and further obtained LDHs-based powder and film materialswith well-defined optical performances. Moreover, we also studied thefabrication regulation, relationship between the structure and photofunction within the materials. By modulating the host-guest andguest-guest interactions, the controllable assembly and tunablephotoemission properties of such materials can be achieved. Severalphotofunctional materials with single-/multi-color emission, polarizedfluorescence, two-photon emission, near-infrared (NIR)absorption/emission and stimuli-responsive fluorescence have beendeveloped. The study have supplied both experimental and computationalbasis for the development of new supramolecular photofunctionalmaterials, the detained contents are listed as follows:1. Based on the band theory and periodic density functional theoretical(DFT) calculation, we have put forward that the valence electronslocalized in the photoactive anions (conjugated polymer, organic smallmolecule and metal complex) are confined within the energy blockingformed by the LDH host layers; therefore, the photoactive moleculeassembled LDH materials can serve as a new type of organic-inorganichybrid multiple quantum well (MQW) structure, beneficial to theenhancement of the photoemission for photoactive molecule. The hybridMQW structure has the new characteristic of host-guest interaction, whichsupplies a theoretical basis for the design and construction ofsupramolecular photofunctional materials.2. Based on the electrostatic layer-by-layer (LBL) deposition technique,we have developed three typical π-conjugated polymer anions (sulfonated poly(p-phenylene)(APPP), phenylenevinylene (APPV), polythiophene(APT)) assembled LDH nanosheet systems, and the obtained ultrathinfilms (UTFs) with uniform blue, yellow and red luminescence present astepwise orderly periodical structure; the thickness, deposited cycle andbrightness of the luminescence can be finely controlled. Compared withthe pure polymer or polyanion/polycation film, the LDH-based hybridUTFs show improved photostability and luminescence properties due tothe suppression of the π-π stacking of polymer backbones. As well, wehave also studied the polystyrene sulfonate assembled LDH materialsusing an in situ polymerization process, and polymers with sheet-likemorphology can be obtained by the use of LDHs layers as template.3. Previously, LDH nanosheets can only assemble with polymers for theconstruction UTFs systems, herein, as the first examples, we haveachieved a series of metal complex (such as tris(1,10-phenanthroline-4,7-diphenylsulfonate) ruthenium and zinctetrasulfophthalocyanine) and small organic anions (such as sulfonatedcyanines) assembled LDH UTFs, which feature MQW structure, highpolarized emission and/or NIR absorption/emission properties.Furthermore, we have developed an exfoliation-coassembly LBL strategyto fabricate ordered UTFs based on functional small cations (divalentbis(N-methylacridinium) and monovalent rhodamine6G) and LDHnanosheets as basic building blocks. It can be expected that, by using such method, numerous cationic species can be assembled with LDHmonolayers for designing and fabricating organic–inorganic functionalmaterials, which largely expand the scope and applied fields forsupramolecualr intercalation-assembly study.4. By use of the three primary color principle, we further developed theordered assembly of two-(blue/green, blue/orange, red/blue, red/green)and three-color (blue/red/green) light-emitting UTFs using anions[bis(N-methylacridinium)@polyvinylsulfonate ion pairs and anionicderivatives (APPP, APPV, APT) and Mg-Al-LDHs as building blocks.The rational combination of luminescent components affords precisecontrol of the emission wavelengths and intensity, and multicoloredluminescent UTFs can be precisely tailored covering most of the visiblespectral region. The UTFs are periodic layered structures involvingheterogeneous superlattices associated with individual photoactiveanion–LDH units. These UTFs also exhibit well-defined multicolorpolarized fluorescence with high polarization anisotropy, and the emissivecolor changes with polarization direction. The method for the fabricationof light-emitting materials possesses several advantages compared withconventional synthesis techniques, such as component variability, lowcost, and easy manipulation. Therefore, this strategy provides a new wayof fabricating heterogeneous UTFs with tunable color luminescence aswell as polarized multicolor and white emission. 5. The small organic photofunctional anions (such as perylenetetracarboxylate, benzocarbazole anions, coumarin-3-carboxylate (C3C),sulforhodamine B (SRB)) have been intercalated into the LDH layer. Bycontrolling the layer charge density, chemical composition and theinterlayer content of guest anions, the orientation, aggregation form andhost-guest interaction can be tuned. By introducing a second guest anion,the suppressing aggregation and quenching of fluorescent anions (C3Cand SRB) can be achieved, which confirm that co-intercalation methodcan be used to optimize the photo-function of inorganic–organiccomposites for developing new types of LDH-based dye materials. Withthe aid of solvent evaporation method, we fabricated SRB and C3Cassembled LDH thin films with well-defined polarized fluorescence dueto the intrinsic structural anisotropy of the LDH sheets and regularorientation of the interlayer guest molecules. By employing moleculardynamic (MD) simulation, we have studied the change in the basalspacing, geometric structure and orientational distribution of the aboveinterlayer guests in the intercalation and co-intercalation systems. Theresults illustrate the regulation for the formation and isolation ofaggregation within the LDH layer, which supply a theoretical basis forco-intercalation assembly method.6. By use of both the intercalation-assembly and LBL methods, we haveobtained anionic stilbene derivatives assembled LDH systems, which exhibit two-photon emission as well as sensitive fluorescence changeupon external stimuli (such as temperature, pressure and metal ionssolution). Thus, the layered host-guest materials with thermochromic,piezochromic and ion-induced chromic luminescence have beendeveloped. The reversible transformations of luminescent properties uponrecycling external conditions also guarantee their future practicalapplications as sensors, switches and fluorescent antiforgery devices. MDand DFT calculations demonstrate that the fluorescent stimuli-responsivebehaviors of LDH-based materials are related to changes in the relativeorientation and packing mode of the chromophore in the LDH matrix, andsuch design and assembly principles may also be utilized to fabricateother new types of luminescent intelligent materials sensitive to externalstimuli.