Studies On The Photochromic And Thermochromic Thin Films Based On Host-guest Interactions In Layered Double Hydroxides

Based on the conception of intercalation chemistry, 4-(4-anilinophenylazo)benzenesulfonate (AO5) and azomethine-H (AMH) have been intercalated into layered double hydroxides (LDHs) respectively. Subsequently, their optically transparent thin films have been fabricated by two synthetic methods:solvent evaporation and in situ crystallization method. The two films possess different orientations of LDH crystallites relative to the substrates:the horizontal and vertical, respectively. The influences of both host-guest interactions as well as film orientation on the photochromic and thermochromic behavior of these films have been investigated in detail. The mechanism of photochemical reaction in the confinement region of LDHs was studied.Optically transparent thin films with thermochromic properties have been fabricated by means of cointercalation of different molar ratios of AO5 and SDS into the galleries of a ZnAl layered double hydroxide (LDH). XRD, SEM and AFM show that they are assembled with ab plane of LDH microcrystals parallel to substrates. The preferential orientation of AO5 in the galleries was evaluated by the fluorescence polarization technique; the results show that AO5 anions are accommodated between sheets of ZnAl-LDH as monomeric units with a tilt angleψ(defined as the angle between the transition dipole moment of AO5 with respect to the normal to the LDH layer) of 74°. The composite film exhibits marked thermochromic behavior (light yellow (?) reddish-orange) in the temperature range 35-65℃, which is reversible over a number of heating-cooling cycles. It has been demonstrated that the thermochromic behavior is related to the tautomerism of interlayer AO5 resulting from both host-guest and guest-guest interactions.Two kinds of optically transparent thin films with photochromic properties have been fabricated based on co-intercalation of AO5 and SDS into the galleries of a ZnAl layered double hydroxide (LDH) by two synthetic methods:solvent evaporation and in situ crystallization. The two films possess different orientations of LDH crystallites with relative to the substrates depending on their fabrication method:horizontal and vertical. The relationship between the photochromic behavior of the interlayer chromophore and the orientation of LDH crystallites was studied thoroughly. Moreover, the films exhibit different absorption and wettability characteristics, indicating potential applications of dye-LDH films as photochromic materials and light sensitive switches.Photochromic thin films have been fabricated by means of co-intercalation of AMH and PS with different molar ratios into the galleries of a ZnAl layered double hydroxide (LDH). The photochromism of AMH occurred in a 2D confined inorganic matrix has been studied by steady state and transient UV-vis spectroscopy. The AMH anion undergoes an excited state intramolecular proton transfer from the enol tautomer to trans-keto tautomer after UV excitation, and the relaxed back-isomerization to the ground state of enol tautomer was investigated by transient UV-vis spectroscopy. It is anticipated that the strategy reported in this work can be employed to fabricate a variety of film materials with interesting photochromic or thermochromic properties based on regular arrangements of organic chromophores within an inorganic matrix.