In switchable molecular recognition, 1 O2 stimulus responsive receptors offer a unique structural change that is rarely exploited. The employed [4+2] reaction between 1 O2 and anthracene derivatives is quantitative, reversible and easily implemented. To evaluate the full potential of this new stimulus, a non-macrocyclic anthracene-based host was designed for the modular binding of cations. The structural investigation showed that 1 O2 controlled the atropisomerism in an on/off fashion within the pair of hosts. The binding studies revealed higher association constants for the endoperoxide receptor compared to the parent anthracene, due to a more favoured preorganization of the recognition site. The fatigue of the 1 O2 switchable hosts and their complexes was monitored over five cycles of cycloaddition/cycloreversion.

Hydrogen-bonding catalysts based on (thio)amidoindole moieties were evaluated in the presence of anions as potent anion receptors and/or acidic partners involved in acid–base reactions. In particular, we focused on their behavior at the acid–base half-equivalence point in the presence of basic anions such as fluoride and benzoate salts. Among three isolated X-ray structures, an amidoindole in the presence of fluoride and hexafluorophosphate salts formed, at the acid–base half-equivalence point, an unprecedented sandwich complex between two receptors and a PF6– anion.

Cet article décrit les circonstances de la naissance puis du développement rapide de ce qui devint le « Laboratoire de photophysique et photochimie moléculaire » (LPPM) dans le bâtiment de chimie. Depuis 2007 la photochimie fait partie d'un ensemble pluridisciplinaire, l'Institut des sciences moléculaires (ISM). On rapporte aussi, en parallèle, la création du laboratoire d'optique moléculaire en 1945, qui devint, en 1996, le Centre de physique moléculaire optique et hertzienne (CPMOH) et, en 2011, le Laboratoire d'optique moléculaire et atomique (LOMA). Des collaborations se sont nouées entre chimistes et physiciens au cours du temps.

Low energy interactions induce the formation of molecular assemblies that can display a large variety of sizes and shapes such as dimers, oligomers, colloids, gels, helices, cylinders, etc. These grouping modes mimic human relationships, as people generally flock together according to their affinities. Moreover, chemical reactions, undergone under strong energy interactions, that result in bond breaking and formation of new compounds, can also be compared to human behaviour. The fables usually involve animals but rarely molecules to play the role of human beings. In this article, we report a molecular tale where two different 9-substituted anthracene derivatives compete in a photochemical reaction, simulating the behaviour of a master and a slave, respectively

Photoirradiation of a hydrogen-bonded molecular complex comprising acyclic components, namely, a stoppered thread (1) with a central barbiturate motif and an optimized doubly anthracene-terminated acyclic Hamilton-like receptor (2b), leads to an interlocked architecture, which was isolated and fully characterized. The sole isolated interlocked photoproduct (Φ = 0.06) is a [2]rotaxane, with the dimerized anthracenes assuming a head-to-tail geometry, as evidenced by NMR spectroscopy and consistent with molecular modeling (PM6). A different behavior was observed on irradiating homologous molecular complexes 1⊂2a, 1⊂2b, and 1⊂2c, where the spacers of 2a, 2b, and 2c incorporated 3, 6, and 9 methylene units, respectively. While no evidence of interlocked structure formation was observed following irradiation of 1⊂2a, a kinetically labile rotaxane was obtained on irradiating the complex 1⊂2c, and ring slippage was revealed. A more stable [2]rotaxane was formed on irradiating 1⊂2b, whose capture is found to be fully reversible upon heating, thereby resetting the system, with some fatigue (38%) after four irradiation–thermal reversion cycles.

Interlocked structures containing the classic Hamilton barbiturate binding motif comprising two 2,6-diamidopyridine units are reported for the first time. Stable [2]-rotaxanes can be accessed either through hydrogen-bonded preorganization by a barbiturate thread followed by a Cu(+)-catalyzed "click" stoppering reaction or by a Cu(2+)-mediated Glaser homocoupling reaction.

α-Halogenoacetanilides (X=F, Cl, Br) were examined as H-bonding organocatalysts designed for the double activation of CO bonds through NH and CH donor groups. Depending on the halide substituents, the double H-bond involved a nonconventional CH⋅⋅⋅O interaction with either a HCXn (n=1-2, X=Cl, Br) or a HCAr bond (X=F), as shown in the solid-state crystal structures and by molecular modeling. In addition, the catalytic properties of α-halogenoacetanilides were evaluated in the ring-opening polymerization of lactide, in the presence of a tertiary amine as cocatalyst. The α-dichloro- and α-dibromoacetanilides containing electron-deficient aromatic groups afforded the most attractive double H-bonding properties towards CO bonds, with a NH⋅⋅⋅O⋅⋅⋅HCX2 interaction.

The blending of perfluorinated bile ester derivatives with the gelator 2,3-didecyloxyanthracene (DDOA) yields a new class of hybrid organo- and aerogels displaying a combination of optical and mechanical properties that differ from those of pure gels. Indeed, the nanofibers constituting the hybrid organogels emit polarized blue light and display dichroic near-UV absorption via the achiral DDOA molecules, thanks to their association with a chiral bile ester. Moreover, the thermal stability and the mechanical yield stress of the mixed organogels in DMSO are enhanced for blends of DDOA with the deoxycholic gelator (DC11) having a C-11 chain, as compared to the pure components' gels. When the chain length of the ester is increased to C-13 (DC13) a novel compound for aerogel formation directly in scCO(2) is obtained under the studied conditions. A mixture of this compound with DDOA is also able to gelate scCO(2) leading to novel composite aerogel materials. As revealed by SAXS measurements, the hybrid and the pure DDOA and DC13 aerogels display cell parameters that are very similar. These SAXS experiments suggest that crystallographic conditions are very favorable for the growth of hybrid molecular arrangements in which DDOA and DC13 units could be interchanged. Specific molecular interactions between two components are not always a pre-requisite condition for the formation of a hybrid nanostructured material in which the components mutually induce properties.

The photochemistry and photophysics of a bis-anthracenyl hydrogen-bonding receptor ( 7 -( 3 , 5-bis((6 -( 4 -( anthracen-9-yloxy) butanamido)pyridin-2-yl)carbamoyl)phenylhept-6-ynoate , 2 ) were investigated in a fluid solution. At room temperature, fluorescence and intersystem crossing compete with intramolecular dimerization to form head-to-head and head-to-tail photoproducts, whereas fluorescence is the principal deactivation pathway at low temperature. Time-resolved fluorescence spectroscopy evidences two excimer-like emitting states whose sensitivity to quenching by oxygen is considerably lower than that of intramolecular photodimerization ( K _SV = ca. 450 vs. <100 L mol^−1, respectively). Based on the temperature-dependence and quenching efficiency of photodimerization, a mechanism is proposed in which the ground-state conformation of the tether controls the formation of the HH vs. HT photodimers via a non-emissive intermediate.

New photoactive polymerizable monomers were synthesized in order to photomodulate the mechanical properties of photocurable materials. These monomers are end-capped by at least two polymerizable units (using irradiation wavelength λ1) connected by a spacer including at least one photocleavable unit (irradiation wavelength λ2≠λ1) i.e. aryltriazene or 2-nitrobenzyl core. The photochemical behaviour of these systems was studied in solution and in resin formulations. Their ability to promote the hardening and crosslinking of a curable resin at λ1, then the subsequent degradation or modification of crosslinked resins under an actinic light (λ2) was evaluated by DMA for formulations including these new monomers.These new monomers were shown, in resin formulation, to readily rigidify the material upon λ1 irradiation and for most of them the subsequent photolysis of their internal linkers at λ2 irradiation was followed by a decrease of the hardness at low temperature (−20°C). For one of them (compound 6) λ2 illumination at room temperature provoked the decrease of the mechanical properties of the solid material making it of interest for dental applications.

An organic–inorganic composite material is obtained by self-assembly of 2,3-didecyloxy-anthracene (DDOA), an organogelator of butanol, and organic-capped ZnO nanoparticles (NPs). The ligand 3, 2,3-di(6-oxy-n-hexanoic acid)-anthracene, designed to cap ZnO and interact with the DDOA nanofibers by structural similarity, improves the dispersion of the NPs into the organogel. The composite material displays mechanical properties similar to those of the pristine DDOA organogel, but gelates at a lower critical concentration and emits significantly less, even in the presence of very small amounts of ZnO NPs. The ligand 3 could also act as a relay to promote the photo-induced quenching process.

In this paper, we describe our last discoveries concerning new original organocatalytic systems that take advantages of supramolecular interactions to trigger the Ring-Opening Polymerization of L-lactide. (Thio)Amidoindoles and N,N-dimethylaminopyridine based systems proved to be efficient catalysts that allow an excellent control of the polymerization. In all cases, dual activation of the monomer and the polymer growing chain-end was demonstrated.

A simple and easily available organocatalytic system was developed for the polymerization of lactide. In partnership with tertiary amines, phenol derivatives were demonstrated to be excellent single H-bonding catalysts with high conversion within 24 h. In particular, ortho-, meta- and meta,-meta'-trifluoromethylphenols revealed an amazing capacity for triggering the controlled ring opening polymerization (ROP) of lactide, through a fitted hydrogen-bond with the monomer.

The design and control of molecular self-assembly is of great interest in the development of new molecular architectures with multiple desired functions or properties. In this context, the gelling systems formed by low molecular weight gelators are particularly promising and are the subject of an ever increasing number of studies. A gel consists of one or more gelling agents and a fluid (organic solvent, water, supercritical liquid) which behaves as a visco-elastic material (soft matter) due to the immobilization of solvent molecules in a three-dimensional network. This network results from the self-assembly of the gelling agent into fibres via non-covalent interactions such as hydrogen bonding, π–π stacking, van der Waals and electrostatic interactions, coordination, and charge transfer. Additional non-covalent interactions lead to physical entanglement of the fibres, which creates a 3D network, the fluid being trapped in the nanoscale interstices. A very large quantity of solvent can be imprisoned in the supramolecular network (in the case of supergelators it is not rare to observe more than 104 molecules of solvent per molecule of gelator in the gel composition), thus creating extraordinary variations of the physical properties of the system. These physical gels are usually thermoreversible (reversible sol-gel transition by heating and cooling) and, depending on the molecular structure of the gelling agent and the fluid which is rigidified, it is possible to form nanoscale superstructures such as nanofibres, nanoribbons, nanosheets, nanoparticles, helical windings, etc., which are of interest for materials and nanoobject conception. Thus, owing to their non-conventional behaviour, low molecular weight gelators are very attractive for applications in various areas, including supramolecular templates or matrices, transport and release of drugs, art conservation, cosmetics, sensors, optoelectronics, actuators, etc. However, despite numerous efforts to establish a structure-property relationship for the development of low molecular weight gelling agents, prediction of the gelling ability of a compound is not straightforward. A major challenge today is the rational design of small size molecular gelators coupled with an understanding of the mechanism of gelation. It is also important to develop future green gelators for eco-compatible applications. This thematic series on organogels and hydrogels will address these various points with a particular emphasis on the molecular requirements on the gelling ability, the different approaches for producing molecular gelators, and some techniques used for the characterization and the properties of the gels. It is my great pleasure to act as guest editor of this Thematic Series, which gathers a wide range of expertise to meet the demands of this interdisciplinary field. I warmly thank all the authors who have enthusiastically accepted to contribute to this series which will give the reader a clear overview of this rapidly developing research field and will identify future growth areas. Jean-Pierre Desvergne Talence, July 2010

The mechanism of the ring-opening polymerization (ROP) of lactide catalyzed by two partner hydrogen-bonding organocatalysts was explored. New amidoindoles 4 a,c, thioamidoindoles 4 b,d, amidobenzimidazoles 5 a,c, and thioamidobenzimidazoles 5 b,c were synthesized and used as activators of the monomer. In the solid state and in solution, compounds 4 and 5 showed a propensity for self-association, which was evaluated. (Thio)Amides 4 and 5 do catalyze the ROP of lactide in the presence of a cocatalyst, tertiary amine 3 a or 3 b, which activates the growing polymer chain through hydrogen-bonding. Reactions were conducted in 2-24 h at 20 degrees C; conversion yields ranged between 22 and 100 %. A detailed study of the intermolecular interactions undertaken between the participating species showed that, as expected, simultaneous weak hydrogen bonds do exist to activate the reagents. Moreover, interactions have been revealed between the partner catalysts 4/5+3. ROP catalyzed by these partner activators is thus governed by multiple dynamic equilibria. The latter should be judiciously adjusted to fine-tune the catalytic properties of (thio)amides and organocatalysts, more generally.

Supercritical carbon dioxide is used to prepare aerogels of two reference molecular organogelators, 2,3-bis-n-decyloxyanthracene (DDOA) (luminescent molecule) and 12-hydroxystearic acid (HSA). Electron microscopy reveals the fibrillar morphology of the aggregates generated by the protocol. SAXS and SANS measurements show that DDOA aerogels are crystalline materials exhibiting three morphs: (1) arrangements of the crystalline solid (2D p6m), (2) a second hexagonal morph slightly more compact, and (3) a packing specific of the fibers in the gel. Aggregates specific of the aerogel (volume fraction being typically phi approximately 0.60) are developed over larger distances (approximately 1000 A) and bear fewer defaults and residual strains than aggregates in the crystalline and gel phases. Porod, Scherrer and Debye-Bueche analyses of the scattering data have been performed. The first five diffraction peaks show small variations in position and intensity assigned to the variation of the number of fibers and their degree of vicinity within hexagonal bundles of the related SAFIN according to the Oster model. Conclusions are supported by the guidelines offered by the analysis of the situation in HSA aerogels for which the diffraction pattern can be described by two coexisting lamellar-like arrangements. The porosity of the aerogel, as measured by its specific surface extracted from the scattering invariant analysis, is only 1.8 times less than that of the swollen gel and is characteristic of a very porous material.

In this study, organocatalytic systems containing both basic and acidic sites, which can activate simultaneously the chain end and the monomer, were investigated in the ring-opening polymerization of L-lactide. To this end, equivalent amounts of (N,N-dimethylamino)pyridine (DMAP) and of its protonated form (DMAP center dot HX) were used as a dual catalytic system for L-lactide polymerization initiated by different alcohols. It is shown that the corresponding DMAP/DMAP center dot HX systems are significantly more active than DMAP alone, and yield well-controlled poly(L-lactide). Depending on the reaction conditions, the transesterification reaction can be prevented.

This article describes two-component charge-transfer interaction mediated organogels (CT-gels) derived from anthracene carboxamides obtained from 2-amino-2-hydroxymethyl-1,3-propanediol (TRIS), and 2,3-dialkoxyanthracenes as donors, with 2,4,7-trinitrofluorenone (TNF) as the common acceptor. We demonstrate the versatility of TNF as an electron acceptor in the formation of these gels. The effect of subtle changes in the donor structure on the gelation ability has been investigated by varying the alkyl chain length in the dialkoxyanthracene donors, and by varying the position of the TRIS substituent in the anthracene carboxamide donors. Distinct differences have been observed in the nature of the CT-gels based on these two kinds of anthracene donors. It has been reported in the literature that 2,3-dialkoxyanthracenes form gels on their own in various aliphatic hydrocarbons and alcohols for linear alkyl chains bearing at least 6 carbon atoms (C(6)). In the present study, it is shown that the CT-complex of these molecules with TNF is able to gel many alcoholic and a few hydrocarbon solvents. Also, in the presence of TNF, the 2,3-dialkoxyanthracenes (C(4)-C(5)) which were non-gelators on their own at ambient temperatures, form CT-gels in a number of alcohols. The other series of gelators discussed, the anthracene carboxamides, require the mandatory presence of TNF to form gels. This donor-acceptor complex forms gels in various aliphatic alcohols. Interestingly, the formation of these CT-gels requires rapid cooling in most of the cases. Thermal stability studies with both types of CT-gels indicate an optimum stoichiometry of 1 : 1 between the donor and the acceptor. Dynamic rheological experiments reveal these gels as viscoelastic soft materials, with the mechanical strength of these gels depending on the amount of TNF present. This provides a means to tune the strength of the gel by varying the doping concentration of the acceptor.

N-(3,5-Bis(trifluoromethyl)phenyl)-1H-indole-2-carboxamide 1e is an efficient hydrogen-bonding organocatalyst for the ring-opening polymerization of l-lactide. This new catalytic species does control the dispersity (1.08) and molecular weight (3460 g/mol vs 3064 in theory) of the poly(l-lactides) prepared in 2 h. (1)H NMR analysis showed that compound 1e complexes l-lactide in CDCl(3) through the two available NH groups (amide and indole). In particular, the catalytic species appeared to be mainly the H-bonding donor amide (1e in extended conformation, alone or dimer (1e)(2)) and, to a lesser extend, the dual H-bonding amido-indole (1e in its the pinched conformation). The first X-ray structure of the complex between a H-bonding organocatalyst and l-lactide also revealed a tight H-bonded network between the dimer (1e)(2) and l-lactide.

In contrast to its bis(oxa) analog 1 (DDOA), the hydrocarbon 11 was not found to form organogels with linear alcohols, alkanes, toluene, acetonitrile and other solvents. Whereas the photoreactivity of 1 did not follow the usual behaviour of anthracene derivatives, compound 11, irradiated in cyclohexane, produced the two expected [4+4]cycloadducts 12 and 13 (anti and syn photodimers, respectively). These facts point to the role of the connecting link between the rigid core and the flexible chain for some self-assembled systems. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)