Synthesis and investigation of building blocks for nanodevices


Self-Assembly of Porphyrin J-Aggregates

Ionic self-assembly is the coupling of structurally different building blocks by electrostatic interactions. The use of ionic self-assembly for the synthesis of supramolecular and nanostructured materials has been reviewed [1]. Advantages of this method are the commercial availability of relatively cheap building blocks and the simplicity of the synthesis. Functional materials with interesting optical, electrical, magnetic, thermal, structural, or mechanical properties can be designed by a proper choice of the building blocks. The self-assembly of porphyrins in to nanotube like structures was investigated by several authors [2-4]. The possibility to build nanotubes by ionic self-assembly of porphyrins was investigated theorethically [5] and demonstrated by the authors [6]. It was shown that the nanotubes containing a Sn porphyrin are photocatalytic and can reduce metal ions from aqueous solution [7].
In this work we investigated the aggregation of Meso-tetra(4-sulfonatophenyl)porphine dihydrochloride and Hematoporphyrin IX dihydrochloride and the different routes to functionalize the porphyrin nanotubes by gold.

The nanotubes were composed by mixing aqueous solution (pH2) of the anionic Meso-tetra(4- sulfonatophenyl)porphine dihydrochloride (1) and cationic HematoporphyrinIX dihydrochloride(2). The individual porphyrins under acid conditions self-assemble into J-aggregates and wheel like structures slowly [4,5]. The mixture of cationic and anionic porphyrins forms the aggregates immediately.

Solution and monolayer spectra for the UV–vis experiments were obtained on an Ocean Optics diode array spectrophotometer to confirm the J-aggregates and nanotubes formation.

TEM images were obtained with Hitachi S-4800 electron microscope in STEM mode. Acceleration voltage was 30 kV and emission current was 10 A Working distance was equal to 8 mm. Droplet of sample solution was placed onto the 200 mesh TEM grid with carbon film coating and was allowed to dry at ambient conditions.

J-aggregates having nanostrip-like spatial structure formed from TPPS4 porphyrine in aqueous solution and coated on different substrates are investigated

Chemical structure of meso-tetra (4-sulfonato-phenyl) porphine (TPPS4) AFM image of network formed from TPPS4 J-aggregates. Scan size 4.5 um x 4.5 um. AFM image of stick-like TPPS4 J-aggregates. Scan size 3 um x 3 um.

Snitka V, Rackaitis M, Rodaite R Assemblies of TPPS4 porphyrin investigated by TEM, SPM and UV-vis spectroscopy Sensors and Actuators B-Chemical 109 (1): 159-166 2005

Rotomskis R, Augulis R, Snitka V, et al.Hierarchical structure of TPPS4 J-aggregates on substrate revealed by atomic force microscopy Journal of Physical Chemistry B 108 (9): 2833-2838 2004