Multi-color fluorescence photoswitching in fluorescent diarylethene nanoparticles

Multicolor fluorescent nanomaterials that exhibit multiple distinguishable emission signals are especially attractive due to their potential applications in flexible full-color displays, in next-generation lighting sources, and in probes to decipher multiple biological events simultaneously. Recently, we found that a photoswitchable fluorescent NP composed of a photochromic diarylethene (DAE) and a fluorescent benzothiadiazole (BTD) unit exhibits a remarkable nonlinear fluorescence photoswitching due to the efficient intermolecular FRET process in the densely packed NP state, in which only a small amount of the non-fluorescent closed-ring isomer (quencher) was enough to quench the whole fluorescence signal. This unique property allows us the demonstration of high-contrast multicolor fluorescence photoswitching. In this study, we tried to prepare several photoswitchable NPs, which have a different emission maximum in the fluorescence unit and a different absorption maximum in the closed-ring isomer of the photochromic DAE unit. All compounds showed the giant amplified fluorescence quenching in the NP state. Based on this property, we tried to demonstrate the sequential red-green-blue (RGB) fluorescence color photoswitching in a multicomponent photochromic fluorescent NP containing three different fluorescence-colored molecules and the wavelength-selective multicolor fluorescence photoswitching in a mixture of two emission colored photochromic NPs composed of different pairs of a photoswitching unit and a fluorescence unit upon irradiation with appropriate wavelength of lights. Such multicolor fluorescence photoswitchable systems have great potential for various applications.