Reversible Photo-Switching of the Magnetization of Iron Oxide Nanoparticles at Room Temperature

Decoupling fluorescence and photochromism in bifunctional azo derivatives for bulk emissive structures

Bifunctional molecules that combine independent push-pull fluorophores and azo photochromes have been synthesized to create fluorescent structures upon light-induced migration in neat thin films. Their photochromic and emissive properties have been systematically investigated and interpreted in light of those of the corresponding model compounds. Fluorescence lifetimes and photoisomerization and fluorescence quantum yields have been determined in toluene solution. Kinetic analyses of the femtosecond transient absorption spectra reveal that the fluorophores evolve in a few picoseconds into a distorted intramolecular charge-transfer excited state, strongly stabilized in energy. Radiative relaxation to the ground state occurred competitively with the energy-transfer process to the azo moiety. Introduction of a 10 Å-long rigid and nonconjugated bridge between the photoactive units efficiently inhibits the energy transfer while it imparts enhanced free volume, which favors photoactivated molecular migration in the solid state.

Nematic-like organization of magnetic mesogen-hybridized nanoparticles

A fluid nematic-like phase is induced in monodisperse iron oxide nanoparticles with a diameter of 3.3 nm. This supramolecular arrangement is governed by the covalent functionalization of the nanoparticle surface with cyanobiphenyl-based ligands as mesogenic promoters. The design and synthesis of these hybrid materials and the study of their mesogenic properties are reported. In addition, the modifications of the magnetic properties of the hybridized nanoparticles are investigated as a function of the different grafted ligands. Owing to the rather large interparticular distances (about 7 nm), the dipolar interaction between nanoparticles is shown to play only a minor role. Conversely, the surface magnetic anisotropy of the particles is significantly affected by the surface derivatization.