Comparative photophysical investigation of doubly-emissive photochromic-fluorescent diarylethenes.

Diarylethene molecules showing photochromism and fluorescence properties in both open and closed forms, associated with two different emission colors, are very promising for applications involving ratiometric emissive photoswitches. We report here a complete study on the competition between the multiple photophysical processes involved in the excited states for two sulfone derivatives of benzothiophene-based diarylethene molecules, only differing by the substituent groups on their reactive carbon (methyl for DAE-Me and ethyl for DAE-Et). Steady-state and time-resolved spectroscopy, combined with DFT and TD-DFT calculations, allow a complete determination of the kinetic constants leading to fluorescence and photoreaction pathways in different solvents, and enlighten the specific role of the substituent group in the photophysical properties due to a shielding effect against the solvation environment. The predominant role of the non-radiative deactivation processes in such a family of molecules is shown, and a tentative excited state mechanistic scheme is proposed based on femtosecond transient absorption experiments performed on the closed forms.

Photochromic-fluorescent-plasmonic nanomaterials: towards integrated three-component photoactive hybrid nanosystems.

Silica-coated gold nanorods functionalized with grafted fluorescent and photochromic derivatives were synthesized and characterized. Spectroscopic investigations demonstrated that cross-coupled interactions between plasmonic, photochromic, and fluorescence properties play a major role in such nanosystems, depending on the thickness of the silica spacer, leading to multi-signal photoswitchability.

[Census: spatial trends. The west conforms, the south surprises]. / Recensement: evolutions spatiales. L'ouest confirme, 1e sud surprend.

PIP: Recent changes in the spatial distribution of the population of Reunion are analyzed using 1990 census data.^ieng