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Development of Turn-On Probes for Acids Triggered by Aromaticity Enhancement Using Tricyclic Amidine Derivatives
datasetposted on 2019-05-16, 00:00 authored by Shota Matsumoto, Yasufumi Fuchi, Kazuteru Usui, Go Hirai, Satoru Karasawa
Two 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.
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