Molecular Aggregation State and Electrical Properties of Terthiophenes/Imogolite Nanohybrids

Abstract

Organic/inorganic nanohybrid materials composed of terthiophenes and imogolite were prepared by means of specific surface interaction between a phosphonic acid group in terthiophene derivatives and aluminol groups on the surface of imogolite. The new materials were investigated by FTIR, UVvis absorption, fluorescence spectroscopy, TEM observation, nitrogen adsorptiondesorption, and IV measurement. Addition of terthiophene of phosphonic acid derivatives into imogolite brought some changes in absorption and photoluminescence spectra, suggesting the formation of H-type aggregate on imogolite surface. The analysis of UVvis spectra and nitrogen adsorptiondesorption data provided insight into the effect of molecular structure of terthiophenes on the adsorption and aggregation behaviors on the imogolite surface. In addition, a significant enhanced current flow was observed through imogolite film when imogolite was chemisorbed by electron-withdrawing terthiophenes. In contrast, current flow decreased as the electron-donating terthiophene was chemisorbed on imogolite. A possible mechanism for such phenomena is discussed.Organic electronic devices made up from small molecules of dye neatly linked by self-assembly to solid support are vital components in light energy conversions systems, optical devices, and sensors.1,2 The self-assemblies of molecules are widely found in nature, for instance, chlorophylls which are embedded in the thylakoid membranes of chloroplasts are specifically arranged in rod-shaped aggregate and act as an efficient light-harvesting system for photosynthesis.36 Recently, there has been considerable research interest focused on the study of photo-physicochemical properties, aggregations, and absorption behavior of dye molecules on the surface of inorganic materials. These studies can provide invaluable information that serves as guidance for fabrication of highperformance dye-based electronic devices.710 Such organic/ inorganic hybrid nanomaterials of the dye/solid support aggregates are expected to demonstrate novel nanotechnological applications that the corresponding monomeric dye could not perform.11,12 Nevertheless, the main challenge in this field remains preparation of a stable dye/solid support aggregate with adjustable aggregation structure on inorganic material surfaces.Generally, most dye molecules can self-assemble and adsorb on inorganic material surfaces through simple physisorption. However, given the fundamental and practical significance of better control over the adsorption and aggregation state of dye molecules on solid support, many research groups are involved in the effort to synthesize novel dye structures with anchoring groups attached. The strategy of attaching anchoring group into the dye is very important, in a sense that one can adjust the distance of dye from the surface, controlling the aggregation state of dye, as well as for chemical surface modification. 9 Additionally, it is possible to graft a variety of functionalized and photoactive species (porphyrins, phthalocya...

Nanomaterials From Imogolite: Structure, Properties, and Functional Materials

“…An efficient way to modify a metal oxide surface is to use phosphonate derivatives [126]. This issue has been extensively studied [127][128][129][130][131][132][133][134][135][136] since 2001 and the first report of the chemisorption of octadecylphosphonic acid onto the outer surface of imogolite nanotubes [127]. Successful grafting of organic moieties can be evidenced by dispersing unmodified and modified nanotubes in organic solvents ( Figure 5.8) [131,135,137].…”

Partial Transformation of Imogolite by Decylphosphonic Acid Yields an Interface Active Composite Material

“…The obtained results challenge the commonly used scheme of grafted imogolite, where the phosphonic acid reacts with OH groups on the external wall of imogolite and forms covalent bonds by condensation. [18][19][21][22] IR, 31 The basis for this reactivity is the surface chemistry of imogolite, which is similar to gibbsite. The tube wall is covered in bridging Al 2 (µ-OH) groups that correspond to the crystal face of gibbsite, while the terminal points have Al-OH / Al-OH 2 + groups, similar to the crystal edges of gibbsite.…”

“…However, most of the studies aim to graft octadecylphosphonic acid or other phosphonic acids onto imogolite. [14][15][16][17][18][19][20][21][22] Yamamoto et al were the first to study the chemisorption of octadecylphosphonic acid (ODPA) on imogolite. [14][15] They concluded that ODPA adsorbs to the surface of imogolite.…”

“…The IR results only reveal the reactivity, but not the identity of the resulting phase. [14][15][17][18][19][20][21][22] XRD and SAXS identified changes in the organization of the product, but led to different interpretations. 16,[19][20] Finally, the investigations by microscopy do not have the required resolution to evidence isolated grafted nanotubes with clarity or lack complementary characterization.…”

“…16,[19][20] Finally, the investigations by microscopy do not have the required resolution to evidence isolated grafted nanotubes with clarity or lack complementary characterization. [16][17][18] A possible alternative reaction path for imogolite is the formation of bulk aluminum phosphonates. It is already known for the intercalation of gibbsite and kaolinite with phenylphosphonic acid (PPA) 23 , the modification of aluminum oxide by ODPA 24 and PPA 4 , and the modification of germanium imogolite by ODPA.…”