Resonance Light Scattering And Its Application In Determining The Size, Shape, And Aggregation Number For Supramolecular Assemblies Of Chromophores

Peter J. Collings, Swarthmore College
E. J. Gibbs
T. E. Starr
O. Vafek
Cyril S.-M. Yee , '97
Laura A. Pomerance , '00
R. F. Pasternack

Abstract

Resonance light scattering (RLS) on supramolecular assemblies of chromophores is a sensitive and selective method to extract: size and shape information, but the interpretation of the data is complicated by the large amount of absorption present. By combining extinction and RLS measurements on the same samples of acidified tetrakis(4-sulfonatophenyl)porphine (H4TPPS), a technique is described whereby the scattering spectrum can be "corrected" for absorption. An additional benefit: of this analysis is that the spectrum obtained for these solutions on a spectrophotometer, which is really an extinction spectrum, can be parsed into its absorption and scattering components. The results demonstrate that scattering contributes significantly to the aggregate peak in the extinction spectrum. Knowledge of the absorption and scattering components allows an estimation of the average aggregation number to be made, which for these solutions is on the order of 10(5)-10(6). In addition, static and dynamic light scattering measurements provide evidence for a rodlike aggregate with about 10 000 molecules along its length and about 20 molecules across its diameter.