Switchable fluorescent and solvatochromic molecular probes based on 4-amino-N-methylphthalimide and a photochromic diarylethene

Abstract

New fluorescent photochromic compounds (1-H and 1-Boc) have been synthesized and characterized in different solvents. The fluorescence emission can be switched "on" and "off" with visible light and UV, respectively, by means of the photochromic reaction. The emission wavelength and efficiency strongly depend on the polarity of the solvent. The compounds show a positive solvatochromic effect in the emission maxima, and their fluorescence quantum yield decreases as the solvent's polarity increases (from cyclohexane to dioxane). In solvents more polar than dioxane the emission is too weak and therefore undetectable, and thus 1-H and 1-Boc behave as "normal" photochromic compounds. The photochromic reaction is also sensitive to the environment. A decrease of more than an order of magnitude was found for the quantum yield of the colouring reaction (Phi(OF -> CF)) for 1-H in ethanol compared with cyclohexane, and an about threefold decrease in Phi(OF -> CF) was observed for the compound 1-Boc in polar solvents (compared with apolar solvents). For both compounds the ring-opening reaction was found not to dependent on the solvent. The novel fluorescent molecular switches 1-H and 1-Boc are able to probe the polarity of their microenvironment.