Photochromic organic nanoparticles as innovative platforms for plasmonic nanoassemblies

Design of Collective Motions from Synthetic Molecular Switches, Rotors, and Motors

Precise control over molecular movement is of fundamental and practical importance in physics, biology, and chemistry. At nanoscale, the peculiar functioning principles and the synthesis of individual molecular actuators and machines has been the subject of intense investigations and debates over the past 60 years. In this review, we focus on the design of collective motions that are achieved by integrating, in space and time, several or many of these individual mechanical units together. In particular, we provide an in-depth look at the intermolecular couplings used to physically connect a number of artificial mechanically active molecular units such as photochromic molecular switches, nanomachines based on mechanical bonds, molecular rotors, and light-powered rotary motors. We highlight the various functioning principles that can lead to their collective motion at various length scales. We also emphasize how their synchronized, or desynchronized, mechanical behavior can lead to emerging functional properties and to their implementation into new active devices and materials.

Hybrid Azo-fluorophore Organic Nanoparticles as Emissive Turn-on Probes for Cellular Endocytosis

The development of fluorescent organic nanoparticles, serving as bioimaging agents or drug cargos, represents a buoyant field of investigations. Nevertheless, their ulterior fate and structural integrity after cell uptake remain elusive. Toward this aim, we have elaborated original photoactive organic nanoparticles (d_TEM ∼ 35-50 nm wide) with an off-on signal upon cellular internalization. Such nanoparticles are based on the noncovalent association of red-emitting benzothiadiazole (BDZ) derivatives and azo dyes, acting as fluorescence quenchers. Upon varying the azo/BDZ ratio, we found that quantitative emission quenching could be obtained with only a 0.2:1 azo/BDZ ratio and originated from exergonic oxidative and reductive photoinduced electron transfer from the azo units (Δ_elG⁰ = -0.21 and -0.29 eV, respectively). Such results revisited the origin of emission quenching, often confusedly ascribed to Förster resonance energy transfer. A nonlinear and sharp drop of the emission intensity with the increase in the azo unit density n was observed and presents comparable evolution to a n^-1/3 mathematical law. Thorough biological examinations involving cancer cells prove a receptor-independent endocytosis pathway, leading to progressive cell lighting upon nanoparticle accumulation in the late endosomal/lysosomal compartments. Complete emission recovery of the initially quenched azo/BDZ nanosystems could be achieved by using mefloquine, which caused endosomal/lysosomal disruption, and release of their content in the cytoplasm. Such results demonstrate that the dotlike emission from endosomes actually stems from fully dissociated individual dyes and not integer nanoparticles. They conclude on the high spatial confinement promoted by organelles and finally question its severe impact on functional compounds or nanoparticles whose properties are strongly distance dependent.

High Performance Fluorescent Turn-On Probe for Amitriptyline Based on Hybrid Nanoassembly of Organic-Inorganic Nanoparticles

Fluorescence methods have gained enormous attention due to their ease in use, simplicity, selectivity and sensitivity. Fluorescent chemosensors respond instantly by converting molecular recognition to fluorescent signals. The consumption of pharmaceutical products by living beings is on great increase. The disposal of such compounds in the environment is a matter of great concern as these compounds enter aquatic environment and show accumulation in tissues of aquatic organisms. In the present study, we have utilized naphthalimide based receptors to fabricate organic nanoparticles (ONPs). These ONPs were used for the development of hybrid nanoassemblies, and the developed nanoassemblies were characterized with the help of transmission electron microscopy and dynamic light scattering studies. The photophysical studies were performed and the hybrid assembly developed using receptor 2 demonstrated a turn-on fluorescence emission behavior on binding with Amitriptyline. The present sensing system acted as promising candidate for determination of Amitriptyline among other contending drug molecules. The established system can recognize Amitriptyline up to a detection limit of 48 nM in aqueous medium. Electrochemical recognition studies show binding of hybrid nanoassembly of receptor 2 with Amitriptyline with limit of detection of 21 nM.

Broad-Range Electrically Tunable Plasmonic Resonances of a Multilayer Coaxial Nanohole Array with an Electroactive Polymer Wrapper

Plasmonic assemblies featuring high sensitivity that can be readily shifted by external fields are the key for sensitive and versatile sensing devices. In this paper, a novel fast-responsive plasmonic nanocomposite composed of a multilayer nanohole array and a responsive electrochromic polymer is proposed with the plasmonic mode appearance vigorously cycled upon orthogonal electrical stimuli. In this nanocomposite, the coaxially stacked plasmonic nanohole arrays can induce multiple intense Fano resonances, which result from the crosstalk between a broad surface plasmon resonance (SPR) and the designed discrete transmission peaks with ultrahigh sensitivity; the polymer wrapper could provide the sensitive nanohole array with real-time-varied surroundings of refractive indices upon electrical stimuli. Therefore, a pronounced pure electroplasmonic shift up to 72 nm is obtained, which is the largest pure electrotuning SPR range to our knowledge. The stacked nanohole arrays here are also directly used as a working electrode, and they ensure sufficient contact between the working electrode (plasmonic structure) and the electroactive polymer, thus providing considerably improved response speed (within 1 s) for real-time sensing and switching.

Enhanced Rates of Photoinduced Molecular Orientation in a Series of Molecular Glassy Thin Films

Photoinduced orientation in a series of molecular glasses made of small push-pull azo derivatives is dynamically investigated for the first time. Birefringence measurements at 632.8 nm are conducted with a temporal resolution of 100 ms to probe the fast rate of the azo orientation induced under polarized light and its temporal stability over several consecutive cycles. To better evaluate the influence of the azo chemical substituents and their electronic properties on the orientation of the whole molecule, a series of push-pull azo derivatives involving a triphenylaminoazo core substituted with distinct electron-withdrawing moieties is studied. All resulting thin films are probed using polarization modulation infrared spectroscopy that yields dynamical linear dichroism measurements during a cycle of orientation followed by relaxation. We show here in particular that the orientation rates of small molecule-based azo materials are systematically increased up to 7-fold compared to those of a reference polymer counterpart. For specific compounds, the percentage of remnant orientation is also higher, which makes these materials of great interest and promising alternatives to azobenzene-containing polymers for a variety of applications requiring a fast response and absolute control over the molecular weight.