2022 Volume 71 Issue 3 Pages 119-131
Bicyclic aminonaphthyridine and aminoquinoline derivatives, which were introduced as electron-donor and -acceptor substituents in the frameworks, show specific emissions along with environmental dependence, for instance, solvents, classifying as “push-pull type fluorophores”. The emission behaviors of the several push-pull type fluorophores in response to external stimuli, such as heat, light, vapor, and mechanical stimuli have been discussed previously. In this study, the detection reagents in response to acid and base that utilize the three push-pull type fluorophores are introduced. Regarding the acid response reagents, the Turn-On type fluorophore is triggered by aromaticity enhancement before and after protonations in the dihydroimidazolylnaphthyridine derivatives, and the aromaticity enhancement causes the emission enhancement. In the case of the base response reagents, the two reagents were introduced as a specific response to the amine analogues. In the first reagent, regarding the formation of an exciplex, the 1,5-naphthyridine derivatives are capable of forming the complexes in an excited state (exciplex) in response to the amine analogues that exhibit long emission wavelengths. With regards to the color change of the HCl salt under the HCl condition in the second reagent, the aminobenzoquinoline derivatives react with the HCl, turning the reddish color into no color. Under the ammonium condition as the amine analogue accompanied by the acid-base reaction, the salt color recovers its reddish color. These three detection reagents for the acid and base undergo minor chemical structure changes before and after the responses, therefore the reagents can be reused for further detection.
