Reversible switching of physical and chemical properties can be achieved by light, by means of photochromic substances. A large number of applications are sought for: protection against light, hyper-resolution microscopy, memories, etc. Moreover, photochromic molecules or moieties can be associated to other molecules or moieties with high performance in a given property for the purpose of switching. For example, materials containing photochromic and fluorescent molecules or moieties, interacting at a nanometric scale, are being investigated, for fluorescence photoswitching between OFF (no emission of light) and ON (with emission of light) states.
A general concern is to obtain big effects with small inputs. In this regard, our strategy is based on the exploitation of nanoscale interactions, such as energy transfer or plasmonic effect, in order to amplify photoswitching. In our presentation, we will focus on two aspects:
1. Accelerated photoswitching, in hybrid systems, containing gold nanoparticles and photochromic molecules. Due to plasmonic effect taking place in the gold nanoparticles, an increase of the photoswitching rate of the photochromic molecules is observed.
2. Enhanced photoswitching of fluorescence in nanoparticles containing photochromic and fluorescent moieties. The fluorescence of a large number (up to 400 moieties) can be turned ON or OFF by only one photon. This unconventional phenomenon was obserd in various systems: multichromophoric molecules, nanoparticles containing photochrome-fluorophore dyads, and silica nanoparticles grafted with photochromic and fluorescent moieties. This effect stems from the multiple energy transfer occurring at molecular and nanometric scale.
Various push-pull azobenzene molecular derivatives showing glassy properties have been processed as thin monomeric amorphous films using spin-coating and thermal evaporation in vacuum. This latter deposition technique yielded homogenous thin films whose surface RMS roughness has been found less than 0.3 Å. Contrarily to spin-coated films requiring external poling for SHG emission, evaporated thin films have proved spontaneously active in second harmonic generation (SHG) when probing at 1.907 μm. Heating above Tg and continuous illumination with an Ar+ laser in the sample absorption maximum band caused dramatic and irreversible disappearance of the spontaneous SHG signal. Applying an external static electric field by using corona discharge induced SHG reversible modulation whose sign has been tuned by changing the bias from positive to negative. Films obtained by vacuum evaporation under a 4 kV voltage underwent considerable morphology changes characterized by the formation of stable 250 nm high nanoclusters evidenced by AFM imaging. The dramatic decrease in SHG has been attributed to the formed nanopillars whose growth depends apparently on the substrate polarization state and must obey a centrosymmetric organization.
Hybrids organic-inorganic nanocomposites are obtained though the hydrolysis and condensation of diethoxymethylsilane and methyltriethoxysilane alkoxides with or without the use of Lewis acids such as Zr(OPrn)4 or Al(etac)(OBus)2 precursors. These materials which present both reductive and hydrophobic behavior are performant host matrices for rare-earth cations and for photochromic dyes such as from spirooxazines (SO), diarylethene derivatives (DE) and furylfulgides (FF). We report the room temperature synthesis of new Eu2+ doped hybrid materials together with their absorption and emission properties. The photochromic properties of the different dyes (SO, DE, FF) in these hybrid solid matrices are also described. Very fast kinetics of coloration and thermal fading (0.2 s-1) are reproducibly evaluated for spiroxazines, while for the first time, quantum yields of the coloration process of diarylethene derivatives and furylfulfydes embedded in solid sol-gel derived matrices are measured.
Several dyes such as a spiropyran, a spirooxazine and two tetraarylporphyrins have been incorporated inside hybrid organic-inorganic matrices synthesized through the acid hydrolysis of dimethyldiethoxysilane and zirconium n- propoxide. These matrices are nanocomposites with well defined hydrophilic (zirconium oxopolymer nodules) and hydrophobic (polydimethylsiloxane chains) domains. As a consequence, they are good candidates to investigate dye-matrix interactions in matrices containing transition metal. These interactions are shown to occur through hydrogen bonds, covalent bonds or Lewis acid-base type bonds. They strongly modify the optical response of the dyes (absorption-emission spectra, lifetime, kinetics...).
Thin films of new side-chain polyimides bearing disperse red one (DR1) groups have been poled by the corona technique assisted by visible irradiation at low temperatures, far below the high glass transition temperature (Tg) of these polymers. The second harmonic generation (SHG) signal reached at the end of this photoassisted poling process is higher than with thermal poling. Furthermore, by a simple method based on absorption measurements with polarized light at variable incidence, it has been shown that the degradation ratio of the chromophores is much lower with photoassisted poling than with thermal poling at a temperature near Tg.
Conference Committee Involvement (4)
Molecular and Nano Machines IV
1 August 2021 | San Diego, California, United States
Molecular and Nano Machines III
24 August 2020 | Online Only, California, United States
Molecular and Nano Machines II
13 August 2019 | San Diego, California, United States
21 August 2018 | San Diego, California, United States