We present here a new example of aggregation-induced emission enhancement (AIEE), which involves an original mechanism based on the formation of organic ion pairs. The phenol 4-hydroxy-7-nitrobenzoxadiazole (NBDOH) is dissociated in water at pH 5.0 to give the corresponding phenolate, which is poorly fluorescent in this medium. We bring evidence that fluorescence quenching is due to an interaction with water molecules. In the presence of a relatively bulky ammonium salt, specifically tetrabutylammonium bromide (TBAB), NBDOH forms a hydrophobic salt, TBA(+)NBDO(-). This has no influence on the fluorescence of the anion as long as the salt is dissolved. However, the salt readily crystallizes in the medium and transition to the solid state is accompanied by a strong increase in fluorescence intensity. This effect can be explained by two reasons. The anions are protected from water molecules, and above all, the presence of the bulky cations prevents parallel-stacking of the anions, thus leading to an original molecular arrangement that is favorable to fluorescence. As the nature of the organic cation may be easily changed, the versatility of the system is very interesting for the design of new organic micro- and nanoparticles that must be fluorescent in the solid state, possibly in an aqueous environment.

Dedicated to Patrick Cassoux to let him know that the dream of a TTF[Ni(dmit) 2 ] 2 -based device may come true!The preparation of thin films of crystalline molecular organic materials with specific physical properties (magnetic order, metallic behavior, superconductivity, etc.) is an active field boosted by the ever-increasing availability of remarkable new materials and their potential applications.[ , due to the high conduction activation barriers induced by grain boundaries.[2]Here, we present results on the preparation of metallic thin films of the molecular metal TTF[Ni(dmit) 2 ] 2 , where dmit 2± = 1,3-dithiole-2-thione-4,5-dithiolato, by electrocrystallization, using silicon wafers as electrodes. TTF[Ni(dmit) 2 ] 2 single crystals (obtained by a diffusion process) exhibit metallic behavior down to 3 K, with r RT~3 00 S cm ±1 and superconductivity is observed at T c = 1.6 K under application of a hydrostatic pressure of 7 kbar.[6] Our films exhibit metallic character down to ca. 12 K in spite of their polycrystalline morphology. Electrocrystallization is the most suitable technique to obtain charge transfer (CT) compounds. [7] The advantages of this technique over, e.g., vapor-phase deposition methods [8] include precise control of the concentration of solute at the interface, the ability to fabricate thin films on substrates with unusual geometries, and the fact that vapor-phase deposition is limited to sublimation/evaporation of neutral species. Although the electrocrystallization technique has been extensively used, the utilization of substrates as electrodes is rare. [9] On the other hand, there is great interest in characterizing hybrid organic±silicon structures. Molecular materials have been shown to be complementary to inorganic-based materials (organic light-emitting diodes, organic thinfilm transistors, etc.), and certain applications are receptive to their substitution because they can be processed as thin films at lower cost.[10]Electrodeposition of TTF[Ni(dmit) 2 ] 2 was carried out with intrinsic Si(001) as the anode and a platinum wire as the cathode. We have selected silicon single crystals as substrates in order to eliminate spurious effects associated with grain boundaries, avoiding, e.g., non-homogeneous current densities. The anodic oxidation of the TTF is performed at constant current density (1.5 lA cm ±2 ) at room temperature. Within 5 days, a black air-stable thin film is formed on the polished face of the (001) Si(001) wafers as anodes in an electrocrystallization process. Scanning electron microscopy (SEM) micrographs of a covered area show a dense film made of roughly spherical grains with sizes ranging from 0.6 to 1 lm (Fig. 1). The estimated thickness of the films is ca. 1 lm. Other works have reported quite different morphologies. Applying a low current density (< 5 lA cm ±2 ), Wang et al. reported electrodeposited films of (BEDT-TTF) 2 PF 6 as 100 lm long needles.[9] When the current density values were increased (> 10 lA cm ±2 ), they ob-

A solvent-exchange process was applied to three fluorescent dyes belonging to the 2-benzimidazolyl-7-diethylaminocoumarin series (namely Coumarin 7 (1), Coumarin 30 (2), and one of their derivatives bearing a butyl chain (3)). The three compounds only differ by the substitution of the nitrogen atom of the benzimidazolyl group. They were first dissolved in acetone and then suddenly placed in an aqueous environment where they generated molecular assemblies. The size and shape of the latter were studied by fluorescence microscopy and transmission and scanning electron microscopy. It appeared that 1 gave aggregates and flat microcrystals that evolved toward elongated structures. 2 formed straight nanofibers that are 10-20 microm long and exhibit a crystal structure. 3 gave short fibers (1 micromx25 nm), which finally arrange into entangled solid nanofibers. The formation of fibers arising from low-molecular-weight molecules was particularly interesting. The optical properties of the free-standing particles in suspension were analyzed and compared to those of highly dilute dyes, with the aim to get additional information about the dye arrangement in the nanostructures.