Journal of Photochemistry and Photobiology A: Chemistry 167 (2004) 31–35 Layer-by-layer self-assembly of polyelectrolyte and the divalent salt of fluorescein E. Nicol a,b,1 , A. Moussa a,b , J.-L. Habib-Jiwan b,∗ , A.M. Jonas a a Unité de Physique et de Chimie des Hauts Polymères, Université catholique de Louvain, Place Croix du Sud 1, B-1348 Louvain-la-Neuve, European Union, Belgium b Unité de Chimie des Matériaux, Université catholique de Louvain, Place Louis Pasteur 1, B-1348 Louvain-la-Neuve, European Union, Belgium Received 6 April 2004; received in revised form 6 April 2004; accepted 13 April 2004 Available online 20 June 2004 Abstract Smooth organic thin films have been obtained by repeated surface complexation between a polycation and fluorescein di-sodium, a divalent organic anion, in a layer-by-layer (LbL) fashion. UV-Vis and thickness measurements show a linear growth of the multilayer as a function of deposition cycles, and indicate that the dye is in a J-aggregate state in the multilayer. The dynamical properties of the multilayer, which are assessed by time-dependent UV spectroscopy, indicate the existence of two relaxation processes. The faster one is due to slow drying and thermal equilibration of the film. The slower process results from spatial rearrangement of dyes in the multilayer, leading to a lower aggregation rate. © 2004 Elsevier B.V. All rights reserved. Keywords: Polyelectrolyte multilayer; Self-assembly; Fluorescein; Thin films 1. Introduction A few years ago, Decher and coworkers developed a new technique of thin film assembly based on the alternate ad- sorption of oppositely charged polyelectrolytes [1]. This method has been extended to various organic or inorganic materials and substrates [2]. Among the large diversity of available compounds, bola-amphiphiles coupled to polyelec- trolytes were used to build thin films [3,4]. Organic dyes were also tested as film components in many investigations [5–11]. Water soluble organic dyes are, gen- erally, aromatic charged molecules. Ariga et al. studied a large variety of dyes bearing different numbers of charges [5]. Quartz crystal microbalance measurements revealed that the dye adsorption occurs as rapidly as the polyion adsorp- tion. They found that well-packed monomolecular layers are formed and depend on size, number of charges and spa- tial orientation of dye molecules. Self-assembly of cyanine [7,8] and pyrene [9] dyes were investigated by UV-Vis spec- troscopy. Inclusion of ruthenium complexes in multilayers ∗ Corresponding author. Tel.: +32-10-47-87-09; fax: +32-10-47-29-89. E-mail address: habib@chim.ucl.ac.be (J.-L. Habib-Jiwan). 1 Present address: Polym` eres, Collo¨ ıdes, Interfaces, UMR CNRS 6120, Universit´ e du Maine, Avenue Olivier Messiaen, 72085 Le Mans, Cedex, France. led to the elaboration of light emitting electrochemical de- vices [10,11]. Surprisingly, to our knowledge, no work deals with the self-assembly of fluorescein salts with polycation. Yet, this dye is one of the most common fluorophore and is exten- sively employed in the field of biochemistry [12]. In a previ- ous work, we reported on the introduction of fluorescein as third component in multilayers made of a polycation and a polyanion [13]. Inward and outward diffusion of the dye in the films were studied. This work deals with the direct alter- nate assembly of the di-anion fluorescein disodium salt with two strong polycations. The multilayer growth is studied by UV-Vis spectroscopy and ellipsometry. The films structure is analyzed by X-ray reflectometry. A rapid investigation of the dynamical behavior of the multilayer is also conducted. 2. Experimental section 2.1. Materials Fluorescein disodium salt dihydrate 90% was purchased from Acros Organics and was used without any further pu- rification. As polycation, we used a poly(vinylbenzyl chlo- ride) (PVBC) quaternized with N,N-dimethylethanolamine 1010-6030/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jphotochem.2004.04.009