Photoswitching in diarylethene nanoparticles, a trade-off between bulk solid and solution: towards balanced photochromic and fluorescent properties

Nanoparticles of 1,2-bis[4'-methyl-2'-(2 ''-pyridyl)thiazolyl]perfluorocyclopentene (1) were prepared by laser ablation (355 nm) of microcrystalline powder suspensions in a water-sodium dodecylsulfate medium. AFM studies coupled with microfiltrations reveal that the resulting suspension is mostly made of nanoparticles with 25 +/- 10 nm diameters. The resulting yellow transparent colloidal aqueous suspension is both photochromic (Phi(OF -> CF) = 0.20 and Phi(CF -> OF) = 0.96) and fluorescent (Phi(F) = 0.017). 1 is not photochromic in the bulk solid, whereas it is only weakly fluorescent in CH3CN (Phi(F) = 0.005); thus, the nanoparticles present a trade-off between these two states where the two properties show reasonable efficiencies. Upon UV irradiation of the opened form of 1, the fluorescence of the colloidal suspension decreases and shows a bathochromic shift. The emission is recovered upon visible irradiation. Such a behaviour enables us to consider nanoparticles of 1 as a ratiometric fluorescent photoswitch.