A Single Photochromic Molecular Switch with Four Optical Outputs Probing Four Inputs

Abstract

Many researchers have considered how to exploit molecular properties, with their intrinsic diversity, to create molecular switches. The use of photochromic compounds, such as spiropyran and diarylethene, as photoswitching systems attracts much attention because of their potential ability for application in photonic devices, where each isomer of the photochromic compound can represent ª0º or ª1º of a digital binary code.[1] Raymo and Giordani [2] demonstrated the modulation of pyrene fluorescence in the presence of spiropyran under three external inputs (ultraviolet (UV) and visible (vis) light and protons) by taking advantage of the different absorption properties of three states of spiropyran, which was proposed for use in multichannel signal communication. Zhu and coworkers proposed a new molecular logic circuit based on the fact that the excimer fluorescence of bis-pyrene can be reversibly regulated by UV light, metal ions, and visible light in the presence of spiropyran. [3] However, these multi-channel signal communication systems relied on two molecules per system. In fact, one key aspect sought in the progress of molecular switching technology is the development of smarter systems that integrate several switchable functions into a single molecule.[4±6]1,2-Bis(thienyl)ethene derivatives (BTEs)±metalloporphy-rin switches, in which the transition metal is coordinated to the ends of the pyridyl-derived BTE, were suggested to achieve non-destructive readout using phosphorescence instead of fluorescence changes. [6a,b] The interaction between the metal ions located at both ends of the pyridyl groups of the diarylethene can be switched by irradiation, because the p-conjugated bond structures between the two aryl groups in the two isomers are different. [7,8] On the other hand, reversible changes of luminescence of BTEs are interesting from the viewpoint of applications for erasable memory media, optical switches, and fluorescence probes. Irie et al. [9] have shown that digital switching of the fluorescence of diarylethene molecules can be controlled by irradiation with UV/vis light at the single-molecule level. Based on the changes of near-infrared (IR) luminescence along with photochromism, a novel family of photochromic BTE-based tetraazaporphyrin or phthalocyanine hybrids was developed in our lab as excellent, non-destructive readout media for application in optical switches.[10]In this communication, a photochromic pyridine-tethered BTE (Py-BTE), namely bis(5-pyridyl-2-methylthien-3-yl)cyclopentene (see Scheme 1), [11a] is used as a photoswitch responding to metal ions, protons, and alternating UV/vis light irradiation. The compound Py-BTE has a special selective response to Zn 2+ and is also very sensitive to protons. The fluorescent properties, including the intensity and emission peak wavelengths of the compound, can be reversibly regulated by UV-vis light, Zn 2+ , and protons. Based on these results, a complicated molecular switch is proposed. To the best of our knowledge, it is the first time that o...

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