Michel Frigoli

Light-Driven Directed Motion of Azobenzene-Coated Polymer Nanoparticles in an Aqueous Medium

Azobenzene-coated polymer nanoparticles in the 16-nm-diameter range act as phototriggered nanomotors combining photo to kinetic energy conversion with optical control through light intensity gradients. The grafted dyes act as molecular propellers: their photoisomerization supplies sufficient mechanical work to propel the particles in an aqueous medium toward the intensity minima with velocities of up to 15 μm/s. It is shown that nanoparticles can be driven over tens of micrometers by translating the intensity gradients in the plane. The analysis of the particles motion demonstrates the decisive role of photoisomerization in the transport with a measured driving force that is 3 to 4 orders of magnitude higher than optical forces.

Bridging the visible: the modulation of the absorption by more than 450 nm.

The coexistence of 18 isomers, identified by NMR spectroscopy and gathered into six states with very different absorption properties, is observed upon irradiation with selective wavelengths of a triphotochromic system joining two naphthopyran entities through a dithienylethene bridge. The sequential electronic coupling of photochromic groups resulted in an absorption behavior reaching far into NIR.

Electrochemical, linear optical, and nonlinear optical properties and interpretation by density functional theory calculations of (4-N,N-dimethylaminostyryl)-pyridinium pendant group associated with polypyridinic ligands and respective multifunctional metal complexes (Ru(II) or Zn(II)).

The synthesis, linear optical and nonlinear optical properties, as well as the electrochemical behavior of a series of pro-ligands containing the 4-(4-N,N-dimethylaminostyryl)-1-methyl pyridinium (DASP(+)) group as a push-pull moiety covalently linked to terpyridine or bipyridine as chelating ligands are reported in this full paper. The corresponding multifunctional Ru(II) and Zn(II) complexes were prepared and investigated. The structural, electronic, and optical properties of the pro-ligands and the ruthenium complexes were investigated using density functional theory (DFT) and time-dependent (TD) DFT calculations. A fairly good agreement was observed between the experimental and the calculated electronic spectra of the pro-ligands and their corresponding ruthenium complexes. A quenching of luminescence was evidenced in all ruthenium complexes compared with the free pro-ligands but even the terpyridine-functionalized metal complexes exhibited detectable luminescence at room temperature. Second order nonlinear optical (NLO) measurements were performed by Harmonic Light Scattering and the contribution of the DASP(+) moieties (and their relative ordering) and the metal-polypyridyl core need to be considered to explain the nonlinear optical properties of the metal complexes.

Room temperature photochromic liquid crystal [3H]-naphtho[2,1-b]pyrans—photochromism in the mesomorphic state

Photochromic liquid crystals based on [2H]-chromenes functionalised in the 3,3[prime or minute]-positions by phenyl groups linked to 4-cyano-4[prime or minute]-hydroxybiphenyl groups via alkyl and siloxane spacers as chromophore were synthesised and the photochromic and mesomorphic behaviour was investigated.

Unraveling Triplet Excitons Photophysics in Hyper-Cross-Linked Polymeric Nanoparticles: Toward the Next Generation of Solid-State Upconverting Materials

The technological application of sensitized upconversion based on triplet-triplet annihilation (TTA) requires the transition from systems operating in liquid solutions to solid-state materials. Here, we demonstrate that the high upconversion efficiency reported in hyper-cross-linked nanoparticles does not originate from residual mobility of the embedded dyes as it happens in soft hosts. The hyper-reticulation from one side blocks the dyes in fixed positions, but on the other one, it suppresses the nonradiative spontaneous decay of the triplet excitons, reducing intramolecular relaxations. TTA is thus enabled by an unprecedented extension of the triplet lifetime, which grants long excitons diffusion lengths by hopping among the dye framework and gives rise to high upconversion yield without any molecular displacement. This finding paves the way for the design of a new class of upconverting materials, which in principle can operate at excitation intensities even lower than those requested in liquid or in rubber hosts.

The Investigation of a Functionalised Photochromic Mesogen

ABSTRACT Most liquid crystalline photochromic systems rely on a structure, where the mesogenic group and the photochromic groups are separated by spacers. This approach uses up easily functionalisable sites for introducing LC behaviour. In this report we present a system where the mesomorphic group is integrated into the photochromic group and the termini of the alkyl groups are functionalised as olefins, which can be reacted further. The synthesis and the investigation of properties and the solid state structure are reported.

A photochromic liquid crystal system

Switching molecular or supramolecular systems reversibly from one state to another, with both states having significantly different properties using light is widespread in biological systems and has been in the focus of materials research for many years. Such synthetic systems are promising as high density data storage systems, sensors, photonic switches or as molecular logic gates. There the concept of optically addressable molecules promises miniaturisation to the molecular level and potentially the direction towards optical computing on that level. Our approach is based on the concept that the functional groups and the properties in such molecules, if suitably selected can add up to attractive properties in the self-assembled molecular systems. Rational design allows of the photochromic core and the mesogenic groups for the modulation of the photochromic behaviour, the absorption properties, the quantum yields of the photo conversion processes and the conversion obtained at the photostationary state. The use of suitable mesogens allows for the use of the FRET effect for the switching behaviour.