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International Journal of Photoenergy
Volume 2006, Article ID 72383, 7 pages
http://dx.doi.org/10.1155/IJP/2006/72383

Aggregation modes of anionic oxacarbocyanines with polycations in solution and in ESAMs

Dipartimento di Chimica, Università di Modena e Reggio Emilia and INSTM, Via Campi 183, Modena 41100, Italy

Received 30 June 2006; Revised 13 August 2006; Accepted 6 September 2006

Copyright © 2006 Andrea Lodi and Glauco Ponterini. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Interaction of oxacarbocyanines D-G with three polycations in aqueous solutions results in the formation of two types of likely small, distorted aggregates rather than the classical J aggregates. On the contrary, the latter are extensively and almost exclusively obtained in electrostatically self-assembled multilayers (ESAMs) prepared by alternate polycation/dye adsorption on quartz substrates. The J-aggregate growth on supported polycations is qualitatively shared by the four cyanines, a fact that reveals the crucial role of the double anionic substitutions on the dyes. On the other hand, films with D and E, which are known to have a stronger tendency to give dimers in water, exhibit higher J-band intensities and stability upon drying relative to those with F and G. Based on these observations, we suggest that energetic factors associated with cofacial dye/dye van der Waals interactions, ultimately related with the degree of planarity of the conjugated chromophores, may still play a major role in controlling aggregation equilibria in these complex systems.