Theoretical Modeling of TPPS4 J-Aggregates
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).
R. Augulis et al., "Theoretical Modeling of TPPS4 J-Aggregates", Solid State Phenomena, Vols. 97-98, pp. 225-228, 2004