Complexes consisting of earth-abundant main group metals such as silicon with polypyridine ligands are of interest for a variety of optical and electronic applications including as electrochromic colorants. Previous spectroelectrochemical studies with tris(2,2′-bipyridyl)silicon(IV) hexafluorophosphate, [Si(bpy)3](PF6)4, demonstrated an ability to control the color saturation of the potential electrochromic dye, with the intensity of the dye’s green color increasing as the charge state sequentially reduces from 4+ to 1+. In this study, the synthesis of bis(4′-(4-tolyl)-2,2′:6′,2″-terpyridine)silicon(IV) hexafluorophosphate, [Si(ttpy)2](PF6)4, is reported along with electrochemical and spectroelectrochemical analyses. Computational modeling (density functional theory) is used to further elucidate the electrochromic properties of previously reported Si(bpy)3n+ species and the new Si(ttpy)2n+ species. While the homoleptic tris(bidentate)silicon(IV) complexes are attractive as electrochromic dyes for tunable color saturation, the bis(tridentate)silicon(IV) complexes are attractive as polychromatic electrochromic dyes.
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Fundamental studies to emerging applications of pyrrole-BF 2 (BOPHY) fluorophores
BF 2 -based fluorophores, such as the well-known BODIPY (4,4-difluoro-4-bora-3 a ,4 a -diaza- s -indacene) dye, are prevalently used in diverse research areas ( e.g. , bioimaging and chemosensing) as they exhibit promising features including high quantum yields, fine-tuned absorption and emission spectra as well as good photostability and biocompatibility. While BODIPY dyes are most commonly used in such applications, other BF 2 -based fluorophores, such as BOPHY (bis(difluoroboron)-1,2-bis((1 H -pyrrol-2-yl)methylene)hydrazine – which possess their own characteristic features – are rising in popularity and are being used in a range of applications spanning from molecular sensors to photosensitizers for solar cells. This review examines select examples of BOPHY dyes to highlight the progression of their development while detailing their syntheses and photophysical properties including structure–property relationships. Applications of a number of substituted BOPHYs made by the methods described in this review are also presented.
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- Award ID(s):
- 1807428
- PAR ID:
- 10275091
- Date Published:
- Journal Name:
- Chemical Society Reviews
- Volume:
- 50
- Issue:
- 9
- ISSN:
- 0306-0012
- Page Range / eLocation ID:
- 5631 to 5649
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The borondipyrromethene (BODIPY) chromophore is a versatile platform for the construction of photoresponsive dyes with unique properties. Specifically, its covalent connection to a photocleavable group can be exploited to engineer compounds with photoswitchable fluorescence. The resulting photoactivatable fluorophores can increase their emission intensity or shift their emission wavelengths in response to switching. Such changes permit the spatiotemporal control of fluorescence with optical stimulations and the implementation of imaging strategies that would be impossible to replicate with conventional fluorophores. Indeed, BODIPYs with photoactivatable fluorescence enable the selective highlighting of intracellular targets, the nanoscaled visualization of sub‐cellular components, the real‐time monitoring of dynamic events and the photochemical writing of optical barcodes.more » « less
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Abstract Photoinduced electron transfer (PET) in newly assembled dyads formedviametal‐ligand axial coordination of phenylimidazole‐functionalized bis(styryl)BODIPY (BODIPY(Im)2) and zinc tetrapyrroles, that is, zinc tetratolylporphyrin (ZnP), zinc tetra‐t‐butyl phthalocyanine (ZnPc) and zinc tetra‐t‐butyl naphthalocyanine (ZnNc), in non‐coordinatingo‐dichlorobenzene (DCB) is investigated using both steady‐state and time‐resolved transient absorption techniques. The structure of the BODIPY(Im)2was identified by using single crystal X‐ray structural analysis. The newly formed supramolecular dyads were fully characterized by spectroscopic, computational and electrochemical methods. The binding constants measured from optical absorption spectral studies were in the range of ∼104 M−1for the first zinc tetrapyrrole binding and suggested that the two imidazole entities of bis(styryl)BODIPY behave independently in the binding process. The energy level diagram established using spectral and electrochemical studies suggested PET to be thermodynamically unfavorable in the ZnP‐bearing complex while for ZnPc‐ and ZnNc‐bearing complexes such a process is possible when zinc tetrapyrrole is selectively excited. Consequently, occurrence of efficient PET in the latter two dyads was possible to establish from femtosecond transient absorption studies wherein the electron transfer products, that is, the radical cation of zinc tetrapyrrole and the radical anion of BODIPY(Im)2, was possible to spectrally identify. From target analysis of the transient data, time constants of circa 3 ns for ZnPc⋅+:BODIPY⋅−and circa 0.5 ns for ZnNc⋅+:BODIPY⋅−were obtained indicating persistence of the radical ion‐pair to some extent. The electron acceptor property of bis(styryl)BODIPY in donor‐acceptor conjugates is borne out from the present study.more » « less
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