Fluorescence Activation with Photochromic Auxochromes

The inherent reversibility of photochromic transformations can be exploited to switch on and off the fluorescence of appropriate organic chromophores under optical control. In turn, the photoactivation of fluorescence permits the monitoring of dynamic processes in real time as well as the reconstruction of images with spatial resolution at the nanometer level. Thus, the identification of viable structural designs to construct and operate photoactivatable fluorophores on the basis of photochromic processes can translate into the realization of valuable analytical tools for biomedical research. In this context, a strategy was designed to connect a simple photochromic oxazine to essentially any fluorescent chromophore with a pendant formyl group. In the resulting fluorophorephotochrome dyads, the photoinduced interconversion of the photochromic component between its two states controls that ability of the fluorescent component to absorb exciting radiation and emit as a result. Under these conditions, the interplay of two illuminating beams, designed to operate the photochromic component and excite the fluorescent one, respectively, offers the opportunity to switch fluorescence reversibly for multiple cycles. Furthermore, the fluorophorephotochrome dyads described herein can be entrapped within the hydrophobic core of polymer micelles and operated under these conditions in aqueous solutions and within the intracellular environment.