Search

International audience; Organic donor-acceptor-donor (D-AD) polymers or small molecules are widely investigated in organic solar cells (OSC) due to their broad light absorption, narrow band gap, excellent charge mobility and exciton seperation at the interface. However, studies of conjugated small molecules with D-AD molecule structures as photocatalytically active materials are still rare. In this work, we give an unprecedented demonstration that photocatalytic activity can in fact be affected by tuning the D and A. Especially, the EBE trimer, comprising 3,4-ethylenedioxythiophene (E) and benzothiadiazole (B) units, exhibits the best photophysical, chemical and photocatalytic properties compared to other D-AD combinations of D and A. Detailed kinetic studies show that all these trimers in organic solution present relatively long-lived and highly emissive photogenerated singlet excitons (τ = 4-13 ns; φem = 0.5-0.9) as judged by photoluminescence and transient absorption measurements, while in specific cases formation of long-lived triplet states can be identified. Organic microparticles of the trimers are efficiently formed in aqueous solution by nanoprecipitation, and rapid photoinduced electron release/injection to the solvent is evidenced spectroscopically. The results indicate that organic small molecule structures with D-AD structures pave a new pathway for photocatalytic solar-to-chemical energy conversion of novel small organic molecules.

A range of supramolecular interactions can give rise to changes in detected spectroscopic signals, which may, in certain cases, be used for sensing analytes and in optical imaging. Changes in conformation, orientation and concentration of specific analytes can be probed. Here an overview of a range of pertinent optical spectroscopies and underpinning principles adapted to study biological media are described. As well as more popular current spectroscopic techniques, notably a range of luminescence techniques (including time-resolved and polarization methods), emerging non-linear optical approaches are detailed. These are based on both electronic and vibrational spectroscopies, which hold great promise for future in situ studies, in particular when they are combined together to generate multimodal information in real-time monitoring where possible.

In summing up, we have asked each of our authors to provide their view of what the future holds in this exciting and rapidly developing field.

International audience; Selective and sensitive detection of Cu(I) is an ongoing challenge due to its important role in biological systems, for example. Herein, we describe a photoluminescent molecular chemosensor integrating two lanthanide ions (Tb$^{3+}$ and Eu$^{3+}$) and respective tryptophan and naphthalene antennas onto a polypeptide backbone. The latter was structurally inspired from copper-regulating biomacromolecules in Gram-negative bacteria and was found to bind Cu$^+$ effectively under pseudobiological conditions (log K$_{Cu}$$^+$ = 9.7 ± 0.2). Ion regulated modulation of lanthanide luminescence in terms of intensity and long, millisecond lifetime offers perspectives in terms of ratiometric and time-gated detection of Cu$^+$. The role of the bound ion in determining the photophysical properties is discussed with the aid of additional model compounds.

Funding Information: This work was supported by the Associate Laboratory for Green Chemistry‐LAQV which is financed by national funds from FCT/MCTES (UIDB/50006/2020). FCT/MCTES is also acknowledged for supporting the National Portuguese NMR Network (ROTEIRO/0031/2013‐PINFRA/22161/2016, cofinanced by FEDER through COMPETE 2020, POCI, PORL, and FCT through PIDDAC) and for grants PTDC/QUI‐QFI/30951/2017 and 2020.07313.BD (A.S.). China Scholarship Council (S.Y.) is acknowledged. A linear double pyridinium-terminated thread comprising a central chalcone moiety is shown to provide two independent binding sites with similar affinity for cucurbit[7]uril (CB7) macrocycles in water as judged from NMR, UV-Visible and fluorescence spectroscopies. Association results in [2] and [3]pseudorotaxanes, which are both pH and photosensitive. Switching from the neutral chalcone to the cationic flavylium form upon irradiation at 365 nm under acidic conditions provided an enhanced CB7 association (K1:1 increases from 1.2×105 M−1 to 1.5×108 M−1), limiting spontaneous on-thread cucurbituril shuttling. This co-conformational change in the [2]pseudorotaxane is reversible in the dark with kobs=4.1×10−4 s−1. Threading the flavylium moiety into CB7 leads to a dramatic increase in the fluorescence quantum yield, from 0.29 in the free axle to 0.97 in the [2]pseudorotaxane and 1.0 in the [3]pseudorotaxane. authorsversion published

International audience; Due to their similar coordination properties, discrimination of Cu + and Ag + by water-soluble luminescent probes is challenging. We have synthesized LCC4 Eu , an 18 amino acid cyclic peptide bearing a europium complex, that is able to bind one Cu + or Ag + ion by the side chains of two methionines, a histidine and a 3-(1-naphthyl)-Lalanine. In this system, the naphthyl moiety establishes a cation- interaction with these cations. It also acts as an antenna for the sensitization of Eu 3+ luminescence. Interestingly, when excited at 280 nm behaves as a turn-on probe for Ag + (+150 % Eu emission) and as a turn-off probe for Cu + (-50% Eu 3+ emission). Shifting the excitation wavelength to 305 nm makes the probe responsive to Ag + (+380% Eu 3+ emission) but not to Cu + or other physiological cations. Thus, LCC4 Eu is uniquely capable of discriminating Ag + from Cu +. A detailed spectroscopic characterization based on steady state and time-resolved measurements clearly demonstrates that Eu 3+ sensitization relies on electronic energy transfer from the naphthalene triplet state to the Eu 3+ excited states and that the cation- interaction lowers the energy of this triplet state by 700 cm-1 and 2400 cm-1 for Ag + and Cu + , respectively. Spectroscopic data point to a modulation of the efficiency of the electronic energy transfer caused by the differential red-shift of the naphthalene triplet, deciphering the differential luminescence response of LCC4 Eu toward Ag + and Cu + .

A series of functionalized quinoline-based aromatic oligoamide foldamers were prepared in their two enantiomeric forms, comprising an enantiopure terminal camphanyl chiral inducer, which governed the adjacent (P-/M-) helical-handedness. Hierarchical chirality transfer was further investigated in chromophore-appended variants via a range of electronic and vibrational spectroscopic techniques, including circularly polarized luminescence, vibrational circular dichroism and fluorescence. Intense total and polarized photoluminescence (up to phi(lum)=0.39, g(lum)=1.5x10(-3)) was observed in the visible region from these modular multicomponent architectures and a significant influence of positional isomerism was evidenced. The optimal position of a fluorophore substituent on the quinoline hexamers was determined as being position 2 over position 6, as stronger chiroptical features were systematically observed with the 2-positioned derivatives.

Bidirectional electronic energy shuttling is shown to occur between the molecular ring and axle components of a rotaxane. The engineered energetic and kinetic parameters give rise to long-lived, delayed luminescence. Perturbation of the quasi-isoenergetic ring and stopper chromophore excited-state energy levels upon cation binding influences the energy shuttling process, and hence luminescence read-out, representing a new potential mechanism in luminescent molecular chemosensor development

The detection of different biologically relevant species like cations, anions, reactive species and biomolecules is an important challenge. Various chemosensors have been developed for the selective detection of cations like metal ions which play a vital role in our daily physiological life and some toxic metal ions, which cause serious health and environmental problems. Simultaneously, the detection of anions and reactive species is crucial as they also play a vital role in a range of physiological and pathological processes. On the other hand, the study of interactions of nucleic acids with various ligands is an active research area as the binding ligands represent paradigms for drug design in anticancer therapy. In this chapter, various fluorescent chemosensors are reported for the detection of biologically and/or environmentally important species as well as the basic principles involved in the design of the chemosensors for specific analytes associated with problems as well as challenges.

We demonstrate the first example of bidirectional reversible electronic energy transfer (REET) between the mechanically bonded components of a rotaxane. Our prototypical system was designed such that photoexcitation of a chromophore in the axle results in temporary storage of electronic energy in a quasi-isoenergetic “reservoir” chromophore in the macrocycle. Over time, the emissive state of the axle is repopulated from this reservoir, resulting in long-lived, delayed luminescence. Importantly, we show that cation binding in the cavity formed by the mechanical bond perturbs the axle chromophore energy levels, modulating the REET process, and ultimately providing a luminescence read-out of cation binding. Modulation of REET processes represents an unexplored mechanism in luminescent molecular sensor development., Delayed emission due to reversible electronic energy transfer (REET) between chromophores in the axle and macrocycle components of a rotaxane is demonstrated. The REET process can be modulated by metal ion binding in the cavity of the rotaxane.

International audience; The binding of donor-acceptor Stenhouse adducts (DASAs) bearing hydrogenbond recognition groups by Hamilton-type receptors significantly influenced their photoswitching properties by altering thermal barriers to isomerization. The thermal barrier between the most stable linear isomer and the photo-generated isomer is lowered on binding to a receptor, and this barrier is crucial for switching properties. The thermal isomerization was shown to proceed via a stepwise linear-enol-keto mechanism in DMSO where the barrier to tautomerisation is within 2 kJ•mol-1 of that of the rate-determining step, which may be important for analyzing switching properties.

The templated clipping of a ferrocene-grafted isophthalic acid derivative to encircle a hydrogen-bonding axle through the reaction with 1,4-bis(aminomethyl)benzene is described. The constituent electroactive macrocycle of the resultant [2]rotaxane is a homologue of the versatile benchmark tetraamide variant developed by Leigh and co-workers. The relative templating effect of different hydrogen-bonding motifs in rotaxane and pseudorotaxane generation is compared, with yields varying from 0 to 41%. The electrochemical properties and single crystal X-ray structure of a doubly ferrocene-decorated [2]rotaxane are further reported.

International audience; The first study dealing with the self-assembly of an α-amino acid derivative in perfluorocarbons is reported. Rheology, microscopy, and spectroscopy studies revealed that the fluorous sodium Lprolinate derivative 1 self-assembles in perfluorocarbons to form a three-dimensional network of left-handed nano-helices resulting in solvent gelation. Singlet oxygen lifetime measured in a gel of perfluorodecalin was ~ 1000 times longer than in pure water. Low molecular weight gelators (LMWG) are a unique and important class of chemicals that can self-assemble in solution to form a gel, i.e. an entangled network of fibers trapping solvent molecules. These self-assembled soft materials have great potential in various applications, including cosmetics, catalysis, organic electronics, regenerative medicine, drug delivery and cell culture. 1,2 Among the various families of LMWGs discovered so far, those based on α-amino acids have received considerable attention. 2,3 Indeed, α-amino acids

A homologous series of two-station [2]rotaxanes incorporating amino-acid units in the molecular thread has been developed. The degenerate [2]rotaxanes exhibit amino-acid specific shuttling rates between two fumaric stations related to the steric factor associated to the amino-acid side chain, as demonstrated by variable-temperature 1H NMR spectroscopy and exchange spectroscopy (EXSY). This allows tuning of the macrocycle shuttling rate over 4 orders of magnitude, which further has a relatively small solvent dependency., Comment: 7 figures; supplementary information appended

International audience; Synthetic hydrogen-bonding receptors are described, which incorporate a central electroactive ferrocene moiety grafted with two adjacent bis(amido)pyridine motifs and an aliphatic tether (14 and 18 methylene units for 1 and 2, respectively) completing the macrocycle. The crystallographic structure, barbiturate guest-binding studies and electrochemical data are provided for the more strongly-binding macrocycle 2.

An innovative photopatterning process is described that allows, in a single laser-promoted operation, the covalent attachment of a molecule on a surface (2D patterning – xy dimensions) and its photopolymerization to grow micro-/nanostructures with spatial control in a third z-dimension. The surface patterning process, based on nitrene reactivity, was harnessed using the highly fluorescent azide-substituted boron difluoride dipyrromethene (BODIPY) 1 that was prepared in a single synthetic step from the parent pentafluorophenyl BODIPY on reacting with NaN3. Using the laser of a fluorescence microscope (375 nm or 532 nm) 1 could be grafted on adapted surfaces and then homopolymerised. In this study we show that using glass coverslips coated with PEG/high density alkyne groups (density of ∼1 × 1014 per cm2), the patterning process was much more spatially confined than when using PEG only coating. Varying the irradiation time (1 to 15 s) or laser power (0.14–3.53 μW) allowed variation of the amount of deposited BODIPY to afford, in the extreme case, pillars of a height up to 800 nm. AFM and MS studies revealed that the nano/microstructures were formed of particles of photopolymerized 1 having a mean diameter of ca. 30 nm. The emission spectra and fluorescence lifetimes for the patterned structures were measured, revealing a red-shift (from ∼560 nm up to 620 nm) of the maximum emission and a shortening (from ∼6 ns to 0.8 ns) of the fluorescence lifetimes in areas where the density of BODIPY is high. As an application of the patterning process, a figure formed of 136 dots/pillars was prepared. The confocal hyperspectral fluorescence image revealed that the figure is clearly resolved and constituted by highly photoluminescent red dots whose fluorescence intensities and emission color proved to be highly reproducible. SEM and AFM studies showed that the luminescent dots were pillars with a conical shape, an average height of 710 ± 28 nm and a FWHM of 400 ± 20 nm.

International audience; Structural integration of two synthetic water soluble receptors for Ca2+ and Mg2+, namely 1,2-bis(2-aminophenoxy) ethane-N, N, N', N'-tetraacetic acid (BAPTA) and o-aminophenol-N, N, O-triacetic acid (APTRA), respectively, gave novel di- and tritopic ionophores (1 and 2). As Mg2+ and Ca2+ cannot be simultaneously complexed by the receptors, allosteric control of complexation results. Potentiometric measurements established stepwise protonation constants and showed high affinity for Ca2+ (log K = 6.08 and 8.70 for 1 and 2, respectively) and an excellent selectivity over Mg2+ (log K = 3.70 and 5.60 for 1 and 2, respectively), which is compatible with magnesium-calcium ion exchange. While ion-exchange of a single Mg2+ for a single Ca2+ is possible in both 1 and 2, the simultaneous binding of two Mg2+ by 2 appears prohibitive for replacement of these two ions by a single Ca2+. Ion-binding and exchange was further rationalized by DFT calculations.

Among stimulus-responsive molecular ring-on-thread rotaxanes and pseudorotaxanes, variants incorporating photochromic sub-units are attracting considerable attention as their properties and structure can be remotely and precisely controlled, additionally without producing chemical waste. The focus herein is on photoswitching-driven assembly/disassembly and modulation of properties resulting from light-activated isomerization or changes in electronic properties.

International audience; Quinoline oligoamide foldamers appended with non-chiral fluorophores and derivatized with a camphanyl chiral inducer display strong chiroptical properties at tunable wavelengths as proved by CD and CPL spectroscopies. Induced CPL activity with high luminescence dissymmetry factors was observed in the visible range at wavelengths specific to the fluorophores.

Free calcium ion concentration is known to govern numerous biological processes and indeed calcium acts as an important biological secondary messenger for muscle contraction, neurotransmitter release, ion-channel gating, and exocytosis. As such, the development of molecules with the ability to instantaneously increase or diminish free calcium concentrations potentially allows greater control over certain biological functions. In order to permit remote regulation of Ca2+, a selective BAPTA-type synthetic receptor / host was integrated with a photoswitchable azobenzene motif, which upon photoirradiation would enhance (or diminish) the capacity to bind calcium upon acting on the conformation of the adjacent binding site, rendering it a stronger or weaker binder. Photoswitching was studied in pseudo-physiological conditions (pH 7.2, [KCl] = 100 mM) and dissociation constants for azobenzene cis- and trans-isomers have been determined (0.230 μM and 0.102 μM, respectively). Reversible photoliberation/uptake leading to a variation of free calcium concentration in solution was detected using a fluorescent Ca2+ chemosensor.

Iodoperfluooralkylation of terminal alkenes and alkynes is effectively photo-promoted by benzophenone 2 (BP) or the photoreducible copper(II) complex 1. In particular, BP at 1 mol% in methanol upon 365 nm irradiation with a low-pressure mercury lamp (type TLC=thin layer chromatography, 6 W) results in a fast reaction with excellent reaction yields. Complex 1 and BP 2 exhibited very similar reactivity, suggesting that the reactions involving 1 are likely to be governed by the benzophenone photoactivation processes, rather than copper(I)/(II) redox processes. Mechanistic investigations using transient absorption spectroscopy revealed that a deactivation pathway of the benzophenone triplet (3BP*) is via its reaction with the methanol solvent. We propose that the generated radicals, in particular .CH2OH, play a key role in the initiation step forming Rf. by reacting with RfI, Rf. then entering a radical chain cycle. 1H NMR studies provided evidence that a substantial amount (∼7% NMR yield) of the hemiacetal CH3OCH2OH is formed, i.e., the possible by-product of the reaction between .CH2OH and RfI. Finally, DFT calculations indicate that a triplet-triplet energy transfer (TTET) process from 3BP* to perfluorooctyl iodide (C8F17I) is unlikely or should be rather slow under the reaction conditions, consistent with the transient absorption studies.

The introduction of two amine substituents in 4' and 7 positions, leads to the formation of a blue flavylium cation, 7-(N,N'-diethylamino)-2-(9-julolidine)-1-benzopyrilium, which is extremely stable across a wide acidic pH range. The kinetic and thermodynamic constants of the multistate system have been calculated by studying the relaxation kinetics after equilibrium perturbation by addition of base (direct pH jumps) or acid (reverse pH jumps). Except for the cis-chalcone, which is an elusive species, the relative energy levels of the other species could be calculated and a global energy level diagram constructed. The diagram explains that the stability of the diamino compound is due to the high energy level of the hemiketal species, which is difficult to access in acidic medium.

Cobalt nanoparticles (NPs) have been prepared by hydrogenation of the organometallic complex [Co(η 3 -C 8 H 13 )(η 4 -C 8 H 12 )] in 1-heptanol in the absence of any other stabilizer and then transformed into Co 3 O 4 NPs using mild oxidative reaction conditions. After deposition onto glassy carbon rotating disk electrodes, the electrocatalytic performance of the Co 3 O 4 NPs in water oxidation has been tested in 1M NaOH. The activity has been benchmarked with that of state-of-the-art Co 3 O 4 NPs through electrochemically-active surface area (ECSA) and specific current density measurements. Furthermore, the covalent grafting of photosensitive polypyridyl-based Ru II complexes onto the surface of Co 3 O 4 NPs afforded hybrid nanostructured materials able to photo-oxidize water into O 2 , while steady-state and time-resolved spectroscopic measurements gave some further insight into kinetics and pertinent reaction steps following excitation. These first-row transition metal oxide hybrid nanocatalysts display better catalytic performance than simple mixtures of non-grafted photosensitizers and Co 3 O 4 NPs, thus evidencing the advantage of the direct coupling between the two entities for the photo-induced water oxidation reaction.

International audience; Copper(i) is a soft metal ion that plays an essential role in living organisms and Cu+-responsive probes are required to detect Cu+ ions in physiological conditions and understand its homeostasis as well as the diseases associated with its misregulation. In this article, we describe a series of cyclic peptides, which are structurally related to the copper chaperone CusF, and that behave as Cu+-repsonsive probes. These peptide probes comprise the 16-amino acid loop of CusF cyclized by a β-turn inducer dipeptide and functionalized by a Tb3+ complex for its luminescence properties. The mechanism of luminescence enhancement relies on the modulation of the antenna effect between a tryptophan residue and the Tb3+ ion within the probe when Cu+ forms a cation-π interaction with the tryptophan. Here, we investigate the influence of the amino acid sequence of these cyclic peptides on the copper-induced modulation of Tb3+ emission and show that the rigid β-turn inducer Aib-d-Pro and insertion of the Tb3+ complex close to its tryptophan antenna are required to obtain turn-on Cu+ responsive probes. We also show that the amino acid sequence, especially the number and position of proline residues has a significant impact on metal-induced luminescence enhancement and metal-binding constant of the probes.

International audience; A novel fluorescent molecular logic gate 1 is demonstrated as a two-input AND logic gate for the detection of acidity and oxidizability. Designed according to an electron-donor–spacer–fluorophore–spacer–receptor' format, the modules are represented by ferrocene as the electron donor, 1,8-naphthalimide as the fluorophore and piper-azine as the proton receptor. In the presence of elevated concentrations of H + and Fe 3+ , the molecule switches 'on' emitting at λ max = 530 nm with Φ f = 0.060 at 10 −4 M H + and 50 μM Fe 3+. The H + binding and apparent Fe 3+ binding constants determined by fluorimetric titrations in 1:1 (v/v) methanol/water are log β H+ = 8.1 and log β Fe3+ = 4.7. Modulation of the fluorescence output results from controlling competing photoinduced electron transfer (PET) at the ferrocene end and internal charge transfer (ICT) at the piperazine end. Time-resolved fluorescence spectroscopy reveals a single fluorescent lifetime of 5.8 ns, while from absorption transient spec-troscopy a remarkable fast decay signal < 2 ps is observed. Comparison is made with methylpiperazine 2 and piperazine fluorescent pH indicator 3 as model compounds.

International audience; The size-tunable emission of luminescent quantum dots (QDs) makes them highly interesting for applications that range from bioimaging to optoelectronics. For the same applications, engineering their luminescence lifetime, in particular, making it longer, would be as important; however, no rational approach to reach this goal is available to date. We describe a strategy to prolong the emission lifetime of QDs through electronic energy shuttling to the triplet excited state of a surface-bound molecular chromophore. To implement this idea, we made CdSe QDs of different sizes and carried out self-assembly with a pyrene derivative. We observed that the conjugates exhibit delayed luminescence, with emission decays that are prolonged by more than 3 orders of magnitude (lifetimes up to 330 µs) compared to the parent CdSe QDs. The mechanism invokes unprecedented reversible quantum dot to organic chromophore electronic energy transfer.

International audience; Two types of fluorescent logic gates are accessed from two different arrangements of the same modular components, one as an AND logic gate (1) and the other as a PASS 0 logic gate (2). The logic gates were designed with an 'electron-donor-spacer 1-fluorophore-spacer 2-receptor' format and demonstrated in 1 : 1 (v/v) methanol/water. The molecules consist of ferrocene as the electron donor, 4-aminonaphthali-mide as the fluorophore and a tertiary alkylamine as the receptor. In the presence of high H + and Fe 3+ levels, regioisomers 1a and 1b switch 'on' as AND logic gates with fluorescence enhancement ratios of 16-fold and 10-fold, respectively, while regioisomers 2a and 2b are functionally dormant, exhibiting no fluorescence switching. The PASS 0 logic of 2a and 2b results from the transfer of an electron from the excited state fluorophore to the ferrocenium unit under oxidising conditions as predicted by DFT calculations. Time-resolved fluorescence spectroscopy provided lifetimes of 8.3 ns and 8.1 ns for 1a and 1b, respectively. The transient signal recovery rate of 1b is ∼10 ps while that of 2b is considerably longer on the nanosecond timescale. The divergent logic attributes of 1 and 2 highlight the importance of field effects and opens up a new approach for regulating logic-based molecules.

An overview is presented of the representative members of the wide range of supramolecular host–guest complexes and polymers formed through the association of complementary hydrogen-bonding motifs comprising barbiturates (or structurally related cyanurates in specific cases) and Hamilton-type, bis(amidopyridine) receptor motifs, which offer strong selective binding in non-competitive media. A particular emphasis is placed on photoaddressable systems.

A [2]rotaxane, whose thread component comprises a central dibenzylammonium group and 9-alkoxyanthracene stoppers and is hosted by a 24-dibenzo-8-crown bead, undergoes an efficient photocatenation step resulting in a [2]rotaxane-to-[2]catenane topology interconversion via a fully reversible [4p+4p] photocyclomerization of terminal anthracene groups.

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.

International audience; Polymersomes are robust self-assembled vesicular structures that are widely studied in a variety of domains from nanomedicine to artificial cell design [1]. Control over their membrane diffusion properties and structural integrity is crucial for their future development [2]. In particular, a high level of control is mandatory in drug delivery applications where species have to be released at the right place and time. Here, we present a high precision method allowing programmed vesicle rupture with full control in time, space and excitation wavelength for selective cargo-release.We designed an easy and tunable protocol for light-driven specific polymersome rupture controlled in time and space, which combines the advantages of utilizing light as a trigger and the fast release of components from bursting vesicles. Our system is based on laser excitation of hydrophilic dyes loaded in the lumen of distinct giant poly(butadiene)-b-poly(ethylene oxide) polymersomes. Upon excitation, the fast generation of reactive oxygen species leads to an increase of the internal osmotic pressure that can not be compensated fast enough, resulting in subsequent vesicle rupture (Fig. 1). This process allows for a precise and fast release of entrapped species from different compartments. Additionally, such a selective mechanism allows discrimination between two types of vesicles within a group of many and successive triggered release of their content without altering the remaining vesicles. This unique mechanism is shown to selectively rupture polymersomes with high precision, and even to deliver small polymersomes and liposomes.

International audience; Localization of the photosensitizer conjugation site in amphiphilic block copolymers is shown to have a great impact on photodynamic therapy efficiency. To this end, an asymmetric multifunctional derivative of the azadipyrromethene boron difluoride chelate (aza-BODIPY) was synthesized and inserted at specific locations in polypeptide-based rod-coil amphiphilic block copolymers. A study of the photophysical properties of the vesicle nanocarriers, obtained by self-assembly of these copolymers, as well as in vitro tests on two cancer cell lines were performed. This study aims at providing guidelines for the optimization of the synthetic design of therapeutic nanomedicines with minimal amounts of photosensitive molecules.

Structural integration of two synthetic water soluble receptors for Ca

The incorporation of quantum dots (QDs) into chalcogenide glass films is attractive for their luminescent properties. Such QD-doped glass structures could serve as a compact, on-chip light source for planar photonic devices. Typical processing methods such as spin coating have limitations of excessive material waste, little control on the pattern of the film and difficulty for scale-up. To overcome these limitations, this study introduces electrospray as a more versatile processing method and has deposited QD-doped chalcogenide glass thin films. The parameters of the electrospray process are prudently chosen to ensure one or none QD is enclosed per liquid droplet. The transmission electron microscopy imaging of resultant films confirm enhanced QD dispersion with reduced aggregations. Absorption and photoluminescence characterization shows the QD-doped chalcogenide glass films prepared by electrospray maintain signature spectra of QDs from the manufacturer.

International audience; The light-triggered, programmable rupture of cellsized vesicles is described, with particular emphasis on selfassembled polymersome capsules. The mechanism involves a hypotonic osmotic imbalance created by the accumulation of photogenerated species inside the lumen, which cannot be compensated owing to the low water permeability of the membrane. This simple and versatile mechanism can be adapted to a wealth of hydrosoluble molecules, which are either able to generate reactive oxygen species or undergo photocleavage. Ultimately, in a multi-compartmentalized and cell-like system, the possibility to selectively burst polymersomes with high specificity and temporal precision and to consequently deliver small encapsulated vesicles (both polymersomes and liposomes) is demonstrated.

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.

International audience; Two novel naphthalimide-based 'Pourbaix sensors' for redox potential and pH were designed based on a 'fluorophore–spacer 1 –receptor–spacer 2 –electron-donor' configuration. The synthesised molecular logic gates consist of an alkylated 1,8-naphthalimide fluorophore connected to a tertiary amine by a flexible ethylene spacer to a ferrocene moiety via a methylene spacer. The UV-visible absorption and steady state fluorescent properties were examined in methanol and 1 : 1 (v/v) methanol/water. The spectroscopic properties are modulated by internal charge transfer (ICT) and photoinduced electron transfer (PET) mechanisms. A log b H + of 9.2 and 8.7 were determined in 1 : 1 (v/v) methanol/water for the methylated 1 and butylated 2 compounds, respectively. An apparent log b Fe 3+ of 4.2 was determined in 1 : 1 (v/v) methanol/ water at pH 4. Time-resolved spectroscopic studies elucidated the stimulus-modulated photoinduced electron transfer pathways. In the oxidised and protonated state, 1 exhibits a single fluorescence lifetime of 8.5 ns, while an efficient photoinduced electron transfer characterised by a time constant of 20 ps is revealed by femtosecond transient absorption spectroscopy in the absence of a perturbing stimulus.

A detailed study on the photoreduction of the copper(II) precatalyst 1 to generate a highly reactive cuprous species for the copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) click reaction is presented. For the photoactive catalyst described herein, the activation is driven by a photoinduced electron transfer (PET) process harnessing a benzophenone-like ketoprofenate chromophore as a photosensitizer, which is equally the counterion. The solvent is shown to play a major role in the Cu(II) to Cu(I) reduction process as the final electron source, and the influence of the solvent nature on the photoreduction efficiency has been studied. Particular attention was paid to the use of water as a potential solvent, aqueous media being particularly appealing for CuAAC processes. The ability to solubilize the copper-tren complexes in water through the formation of inclusion complexes with β-CDs is demonstrated. Data is also provided on the fate of the copper(I)-tren catalytic species when reacting with O2, O2 being used to switch off the catalysis. These data show that partial oxidation of the secondary benzylamine groups of the ligand to benzylimines occurs. Preliminary results show that when prolonged irradiation times are employed a Cu(I) to Cu(0) over-reduction process takes place, leading to the formation of copper nanoparticles (NPs). Finally, the main objective of this work being the development of photoactivable catalysts of practical value for the CuAAC, the catalytic, photolatent, and recycling properties of 1 in water and organic solvents are reported.

A macrocyclic ring comprising multiple hydrogen-bonding sites as well as metal-chelating sites is shown to play the role of ligand in active templated, copper-catalysed [2]rotaxane formation via Huisgen and Glaser reactions. The crystallographic structure and copper ion binding studies are provided for the free macrocycle, along with molecular modelling, barbital, N,N′-trimethyleneurea and copper (I) binding information for the new rotaxanes.

Sugar-responsive microgels were prepared by the covalent grafting of a poly(N-isopropylacrylamide) (pNIPAM) matrix with phenylboronic acid (PBA) as a saccharide sensing unit and a [Ru(bpy)3](2+) derivative (2,2'-bipyridine) as a luminescent reporter. Time-resolved emission studies reveal that the ruthenium complex has an unusually long lifetime (1.6 μs) and high quantum yield (∼0.17) in the PBA-microgel environment. In the presence of sugars, the microgels swell due to the formation of a sugar-boronate ester, leading to a more hydrophilic polymer chain. The swelling is accompanied by a decrease of the lifetime and the photoluminescence quantum yield, which cannot be explained solely by the swelling of the hydrogel. The emission properties of the ruthenium complex in PBA-functionalized microgels are compared to those in pNIPAM microgels lacking PBA moieties in various swelling states. The presence of PBA in the vicinity of [Ru(bpy)3](2+) is shown to have a predominant impact on its luminescence properties, mainly through a decrease of the polarity. Sugar-induced triggering of the boronate state thus leads to strong variations of the polarity and the luminescence characteristics.

International audience; Reversible electronic energy transfer (REET) may be instilled in bi-/multichromophoric molecule-based systems, following photoexcitation, upon judicious structural integration of matched chromophores. This leads to a new set of photophysical properties for the ensemble, which can be fully characterized by steady-state and time-resolved spectroscopic methods. Herein, we take a comprehensive look at progress in the development of this type of supermolecule in the last five years, which has seen systems evolve from covalently tethered dyads to synthetic molecular machines, exemplified by two different pseudorotaxanes. Indeed, REET holds promise in the control of movement in molecular machines, their assembly/disassembly, as well as in charge separation.

International audience; Persistent self-assembled polymersome capsules are shown to solubilise and stabilize a new hydrosulfide-containing (2), as well as hydroxylated (1), malachite green derivatives in their leuco-forms in aqueous buffer solution. Photoirradiation resulted in reversible hydroxide release/hydrogen sulfide generation. Notably, the efficient augmentation of H2S concentration to physiologically-relevant levels is shown.

International audience; A series of photoactive triads have been synthesized and investigated in order to elucidate photoinduced electron transfer and hole migration mechanism across nanosized, rigid helical foldamers. The triads are comprised of a central helical oligoamide foldamer bridge with 9, 14, 18, 19, or 34 8-amino-2-quinolinecarboxylic acid repeat units, and of two chromophores, an N-terminal oligo(para-phenylenevinylene) electron donor and a C-terminal perylene bis-imide electron acceptor. Time-resolved fluorescence and transient absorption spectroscopic studies showed that, following photoexcitation of the electron acceptor, fast electron transfer occurs initially from the oligoquinoline bridge to the acceptor chromophore on the picosecond time scale. The oligo(para-phenylenevinylene) electron donor is oxidized after a time delay during which the hole migrates across the foldamer from the acceptor to the donor. The charge separated state that is finally generated was found to be remarkably long-lived (>80 μs). While the initial charge injection rate is largely invariant for all foldamer lengths (ca. 60 ps), the subsequent hole transfer to the donor varies from 1 × 109 s–1 for the longest sequence to 17 × 109 s–1 for the shortest. In all cases, charge transfer is very fast considering the foldamer length. Detailed analysis of the process in different media and at varying temperatures is consistent with a hopping mechanism of hole transport through the foldamer helix, with individual hops occurring on the subpicosecond time scale (kET = 2.5 × 1012 s–1 in CH2Cl2). This work demonstrates the possibility of fast long-range hole transfer over 300 Å (through bonds) across a synthetic modular bridge, an achievement that had been previously observed principally with DNA structures.

A molecular barbiturate messenger, which is reversibly released/captured by a photoswitchable artificial molecular receptor, is shown to act as an effector to control ring gliding on a distant hydrogen-bonding [2]rotaxane. Thus, light-driven chemical communication governing the operation of a remote molecular machine is demonstrated using an information-rich neutral molecule.

Iridium(iii) cyclometalated complexes have been used as models to study the effect that extended conjugation and substitution pattern has on the photochromic behavior of azobenzene-appended 2-phenylpyridyl (ppy) ligands. For this purpose four azobenzene-containing ppy ligands were synthesized. With these ligands, nine iridium(iii) complexes containing up to three appended azobenzenes were synthesized. Analysis of their photochromic behaviour by means of UV-vis and (1)H-NMR spectroscopy permitted us to conclude that the light-induced trans-to-cis isomerization of the azobenzene was strongly inhibited upon coordination to the Ir(iii) cation when the electronic conjugation was extended along the whole ligand. The use of an aliphatic spacer unit (either -CH2- or -OCH2-) between the azobenzene and the ppy fragment of the ligand sufficed to disrupt the electronic communication, and obtain photochromic organometallic complexes.