Papers by Keyword: J-Aggregates

Abstract: The mechanism and conditions of meso-tetra (4-sulfonatophenyl) porphine (TPPS₄) molecular aggregate formation and their geometrical structure are investigated by methods of molecular mechanics and quantum chemistry. J- type aggregates are formed of zwitterionic forms of TPPS₄ via interaction of their positively charged porphyrin rings and negatively charged SO₃ - groups. According to ab initio and PM3 calculations it was found that TPPS₄ zwitterion has asymmetrical structure (parts of porphyrin ring are asymmetrically bent out of plane), although the porphyrin ring of TPPS₄ molecule in neutral aqueous solution (at pH 7) is flat and the planes of phenyl rings are nearly perpendicular to the porphyrin plane. We propose that asymmetrical porphyrin rings are able to form bent threads. The thread is bent approx. 5° for each monomer, so approximately 60 monomers should form the loop (diameter ~20 nm).

Abstract: An understanding of both the interactions between the adsorbate molecules and the interactions between adsorbates and the surface is a prerequisite to eventually controlling the selfassembly process in supramolecular aggregation. Here we report the formation of supramolecular structures (J-aggregates) whose size and aggregation pattern are controlled by changing the number of polar sulfonic groups of meso-tetra (4-sulfonatophenyl) porphine. Using atomic force microscopy we show that substituted porphyrin molecules (5,10,15,20-tetrakis(4-sulfonatophenyl) porphine (TPPS₄), 5,10,15-tris(4-sulfonatophenyl)-20-phenyl porphine (TPPS₃), 5,15-bis(4-sulfonatophenyl)- 10,20-diphenyl porphyne (TPPS_2op) - SO₃ groups are opposite each other, and 5,20-bis(4- sulfonatophenyl)-10,15-diphenyl porphyne (TPPS2a) . SO₃ groups are adjacent each other) form different spatial structures. Our findings suggest that placement of functional groups that are participating in direct noncovalent interactions will allow design and construction of different supramolecular structures adsorbed to surfaces.

Abstract: The adsorption of organic molecules on solid surfaces is one of the fundamental processes for the development of molecular-based nanodevices. Here we focus on the adsorption and ordering of the TPPS₄-based J-aggregates on silicon and gold as well as on self-assembled monolayer (SAM) surfaces. The SAMs used for the experiments were based on the chemisorption of thiol containing compounds onto gold. Long ω-substituted alkanethiols are spontaneously assembled on gold to form highly ordered and densely packed layers with controllable chemical and physical properties. TPPS₄ J-aggregates were dispersed on SAM surfaces, and on plain gold and silicon substrates for comparison. The dimensions of aggregates, measured by means of atomic force microscopy, varied depending on the type of substrate. Long stripe-like aggregates were flattened on the substrate surface, and the height and width of aggregates highly correlated with the polarity of surface groups. For example, the J-aggregates were narrower on hydrophobic substrates (with non-polar groups) and wider on hydrophilic substrates (with polar groups). These observations support the hypothesis, that TPPS₄ forms .soft. cylindrical aggregates, that appear flattened on the substrate.

Abstract: Meso-tetra (4-sulfonatophenyl) porphine (TPPS4) is water-soluble tetrapyrrolic dye, which forms self assembled nanostructures – J-aggregates under appropriate conditions. It was shown, that such aggregates survive dried on the substrate. The spatial structure of TPPS4 Jaggregates formed in acidic aqueous solutions and dispersed on silicon substrates was analyzed by means of atomic force microscopy (AFM). The stripe-like structures were observed. The size of individual stripes ranged 4,5×40×(200-1000) nm (H×W×L). The width and height was almost the same for all stripes and independent upon the concentration of the solution, however the length was statistically distributed and the mean length increased with increasing concentration of initial TPPS4 solution. At higher concentrations such stripes stacked into thicker fibers containing 2-20 stripes. Such fibers branched and formed large bush-like structures sized up to several millimeters. According to experimental findings the model of mesostructures, formed by TPPS4 J-aggregates, was proposed.