In
this work, we demonstrate that strain-promoted azide–alkyne
cycloaddition (SPAAC) yields virtually complete conversion in the
context of the post-synthetic modification (PSM) of metal–organic
frameworks (MOFs). We use surface-anchored MOF (SURMOF) thin films,
[Zn2(N3-bdc)2(dabco)], grown on modified
Au substrates using liquid-phase epitaxy (LPE) as a model system to
first show that, with standard click chemistry, presently, the most
popular method for rendering additional functionality to MOFs via
PSM, quantitative conversion yields, cannot be reached. In addition,
it is virtually impossible to avoid contaminations of the product
by the cytotoxic CuI ions used as a catalyst, a substantial
problem for applications in life sciences. Both problems could be
overcome by SPAAC, where a metal catalyst is not needed. After optimization
of reaction conditions, conversion yields of nearly 100% could be
achieved. The consequences of these results for various applications
of PSM-modified SURMOFs in the fields of membranes, optical coatings,
catalysis, selective gas separation, and chemical sensing are briefly
discussed.
By using the Nicholas reaction we managed to design a concise synthesis that only uses three steps to build the eight-membered ring. It was also possible to functionalize said alkyne with a fluorophore.
Imaging iseven these daysstill restricted to of a few classes of robust dyes. A demand for switchable tags led us to the design of a new class of pre-fluorophores. We achieved this by using a non-fluorescent N-(4-azidophenyl)-carbazole tag which turns fluorescent by click reaction with alkynes and cyclooctynes.The spectral properties of the labelled dyes were investigated. Our results suggest that a twisted internal charge transfer (TICT) transition is responsible for the emission. DFT calculations and single-crystal X-ray diffraction of selected examples support this explanation. The feasibility of the new dyes for biological application has also been tested via confocal microscopy.Scheme 1 Synthetic route to N-(4-azido-phenyl)-carbazole 1. † Electronic supplementary information (ESI) available: Characterisation, spectra, computation method and X-ray crystallographic information les for compounds 2 and 3 (CIF). CCDC 936576 and 936577. For ESI and crystallographic data in CIF or other electronic format see
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