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.
We have developed several fluorescence photoswitchable molecules based on a photochromic energy transfer or electron transfer process and successfully demonstrated reversible fluorescence photoswitching with non-destructive readout capability even at the single-molecule level. In this study, as a novel method to achieve reversible fluorescence photoswitching and non-destructive fluorescence readout, we focused on the stimuli-responsive orientation behavior of a liquid crystalline polymer (LCP) containing a photochromic azobenzene unit. We attempted to cooperatively control the molecular orientation of a fluorescent dye by incorporating into an azobenzene LCP (PMAz6Ac) film and reversibly switch the fluorescence intensity along with the orientation change of PMAz6Ac induced by the polarized-light irradiation or thermal annealing process. We successfully observed cooperative orientation behavior of a doped fluorescent dye along with the orientation change of PMAz6Ac by choosing an appropriate fluorescent dye. This cooperative orientation allows us to demonstrate the reversible modulation of fluorescence intensity with non-destructive readout under irradiation with the polarized excitation light.
KEYWORDS: Deposition processes, Nanoantennas, Molecules, Scanning electron microscopy, Gold, Luminescence, Near field optics, Nanoparticles, Plasmonics
In this work, we demonstrate an original single-nanoparticle deposition process based on near-field optical forces
arising from much localized plasmonic resonant gap-mode. At first, nanoparticles exclusively made of fluorescent dye
molecules are fabricated in aqueous colloidal suspension. Near-field optical forces are then used to attract and deposit
single nanoparticles in the nanogap of plasmonic nanoantennas. This one-step deposition process allows targeted
deposition of nanoscale materials directly from a colloidal dispersion to a few-nanometer large area of interest.
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