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Download fileDevelopment of Turn-On Probes for Acids Triggered by Aromaticity Enhancement Using Tricyclic Amidine Derivatives
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posted on 2019-05-16, 00:00 authored by Shota Matsumoto, Yasufumi Fuchi, Kazuteru Usui, Go Hirai, Satoru KarasawaTwo fluorophores consisting of tricyclic
amidine derivatives (DHIm and DHPy) were
prepared as selective turn-on
probes for acids, which were triggered by an aromaticity enhancement.
Both amidine derivatives were expanded rings prepared by condensed
reactions between the corresponding dibromoalkanes and an aminonaphthyridine
analogue. In X-ray analyses, DHIm, in which the dihydroimidazole
ring was condensed into aminonaphthyridine, showed high planarity,
compared to DHPy, with condensed dihydropyrimidine. The
fluorescence properties of DHIm exhibited a higher quantum
yield than DHPy due to the difference in planarity. Under
acidic conditions, such as in the presence of H+ and M(II),
protonations and complexations occurred, exhibiting a higher quantum
yield than the neutral DHX (X = Im or Py). The nucleus-independent
chemical shift values from the density functional theory calculations
suggested that the protonations and complexations caused an enhancement
of the aromaticity within the frameworks. These aromaticity changes
led to intense fluorescence, and DHX behaved as a selective
turn-on probe for acids and metal ions. Interestingly, this fluorescence
turn-on system triggered by the aromaticity-based enhancement is not
a typical system, such as the photoinduced electron transfer, aggregation-induced
enhanced emission, and twisted intramolecular charge transfer systems,
but is classified as a novel turn-on system.
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novel turn-on systemTricyclic Amidine Derivativestricyclic amidine derivativesacidic conditionsmetal ionsX-ray analysesphotoinduced electron transfertheory calculationsquantumfluorescence propertiesAromaticity Enhancementaminonaphthyridine analogueintramolecular charge transfer systemsdihydroimidazole ringcomplexationplanarityDHImDHPyturn-on probeTurn-On Probesprotonationnucleus-independent chemical shift valuesturn-on probesaromaticity changesamidine derivativesaromaticity-based enhancementfluorescence turn-on systemDHXAcids Triggeredaromaticity enhancement