Evidence of the early stage of porphyrin aggregation by enhanced Raman scattering and fluorescence spectroscopy.
The early stage of fractal porphyrin diffusion-limited aggregation (DLA), induced by addition of a polyamine, is observed in aqueous solution by enhanced Raman scattering and fluorescence quenching. The enhancement of Raman scattering is due to nonlinear optical properties typical of fractal composites. Although this early stage (reaction-limited aggregation) has been theoretically predicted (by mean-field theory and molecular dynamics simulation), it is experimentally difficult to observe. During this initial stage, fluorescence quenching gives direct information on the decrease of the concentration of monomeric porphyrins, whereas Raman scattering (through characteristic vibrational modes of the aggregate) reports on the concentration of porphyrins in the aggregated form. These small clusters constitute the seeds for the DLA aggregation process leading to micrometric-sized fractals.
Istituto per i Processi Chimico-Fisici, CNR, Via La Farina 237, I-98123, Messina, Italy. micali@me.cnr.it
Norberto
N
Micali
Valentina
V
Villari
Andrea
A
Romeo
Maria Angela
MA
Castriciano
Luigi Monsù
LM
Scolaro
D003198:Computer Simulation; D003460:Crystallization / Q000379:methods*; D019281:Dimerization; D046911:Macromolecular Substances / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D011166:Porphyrins / Q000737:chemistry*; D013050:Spectrometry, Fluorescence / Q000379:methods*; D013059:Spectrum Analysis, Raman / Q000379:methods*
D046911:Macromolecular Substances; D011166:Porphyrins