Photochromism and Dual‐Color Fluorescence in a Polyoxometalate–Benzospiropyran Molecular Switch

Abstract

Abstract:The photophysical properties of a Keggin-type polyoxometalate (POM) covalently bounded to a benzospiropyran (BSPR) unit have been investigated. These studies reveal that (i) both closed and open forms are emissive with distinct spectral features (λem, (closed form) = 530 nm, λem, (open form) = 670 nm); (ii) the fluorescence of the BSPR unit of the POM-based hybrid is considerably enhanced compared to BSPR reference compounds. While the fluorescence excitation energy of the BSPR reference compounds (370 nm) is close to the intense absorption responsible of the photochromic character (350 nm), the fluorescence excitation of the hybrid is shifted to lower energy (400 nm), facilitating the population of the emissive state. Combined NOESY NMR and theoretical calculations of the closed form of hybrid give an intimate understanding of the structural conformation adopted by the hybrid and show that the nitro-aryl moieties of the BSPR is folded toward the POM, which should affect the electronic properties of the BSPR.Photo-responsive molecules and materials are currently receiving considerable attention regarding their potentiality for the development of advanced photonic devices in various applications such as information storage, optical switches, protection, smart labelling and super-resolution microscopy. [1] Particularly, the elaboration of molecular systems combining photo-switching and fluorescence properties constitute a promising research field because of the high sensitivity, resolution, contrast and fast response times of the fluorescence. Furthermore, the emergence of single-molecule fluorescence spectroscopy opens the route to high memory density nanodevices, in which a single molecule would work as one bit of memory, [2] and thus strongly supports the molecular approach. Until now, the development of molecular systems displaying photo-modulated emissive properties has mostly relied on the association of luminescent and photochromic components in a molecular assembly. [3] In these systems, the transformation of the photochromic component is exploited to modulate the emission intensity of the luminescent component on the basis of electron and/or energy transfer. [4] However, molecular systems displaying tuneable fluorescence features, i.e. having different emission energies, according to the form of the photochromic unit, have been scarcely reported in the literature. [5] The coexistence of photochromic and fluorescence properties, in a single photoactive unit, is rarely achieved since in case of fast internal conversion only one photophysical property (photochromic vs fluorescence) is observed. Furthermore the ns timescale of fluorescence [6] is considerably slower than the fs to ps timescale of the ring opening/closure dynamics occurring in the photochromic events. [7] POMs are nanosized molecular oxo cluster that are currently receiving considerable attention because of their wide range of properties and their potential applications in various fields such as analytical chemistry, medicine and ...

Covalent hybrids based on Re(i) tricarbonyl complexes and polypyridine-functionalized polyoxometalate: synthesis, characterization and electronic properties

“…Many studies on covalently functionalized POMS aimed to combine them with known chromophores. 14 Both organics and organometallic dyes were explored, such as benzospiropyran 15 , porphyrins, 9, 11b, 16 and Ru(II), 6c, 17 Ir(III) 18 and Re(I) 19 polypyridines complexes (Fig. 1).…”

Recent advances in organic‐based materials for resistive memory applications

“…POM molecules are a class of anionic metal‐oxide nanoclusters, which can achieve multiple stable metal‐centered redox states in a narrow potential range 196‐199 . Because of this multiredox behavior, POMs and their organic‐inorganic hybrid derivatives have become a new family of contenders for redox‐based resistive memory electronics 200‐206 …”

A photochromic upconversion nanoarchitecture: towards activatable bioimaging and dual NIR light-programmed singlet oxygen generation

“…1,2 Optogenetics has revolutionized the eld involving the use of light to regulate the neuronal activity in biological systems as complex as live animals. [3][4][5] In particular, molecular photoswitches (e.g., diarylethene (DAE), azobenzene, and spiropyran), which undergo a reversible structure change upon light irradiation, have attracted great attention for biomedical applications, such as photocontrolled cell adhesion, 6 bioimaging, [7][8][9][10][11][12] and drug release. [13][14][15] For example, photoswitchable uorescence probes, whose uorescence can be modulated from a bright-to-dark or two color state through light control, have been developed for bioimaging with improved resolution and specicity.…”

“…[13][14][15] For example, photoswitchable uorescence probes, whose uorescence can be modulated from a bright-to-dark or two color state through light control, have been developed for bioimaging with improved resolution and specicity. [7][8][9][10][11][12] More recently, the employment of molecular photoswitches for controlling the action of therapeutics has enabled the emerging eld of photopharmacology. [16][17][18][19][20] These switching units allow for remote control of the function of bioactive molecules with light, and thus could reduce off-target activity and achieve high precision in treatment.…”