Issue 49, 2020

Fluorescence enhancement of quinolines by protonation

Abstract

A study of the fluorescence enhancement of isoquinoline, acridine (benzo[b]quinoline) and benzo[h]quinoline is reported with six organic acids of different pKa values. Protonation was found to be an effective tool in the fluorescence enhancement of quinolines. A significant increase in the fluorescence intensity is observed only when strong acids are used, resulting in an over 50-fold increase in fluorescence with trifluoroacetic or benzenesulfonic acid and isoquinoline in a 1.5 : 1 ratio. The benzenesulfonic acid was found to be the most effective in the protonation of the bases despite its higher pKa value compared to trifluoro- and trichloroacetic acid. The X-ray crystal structures of 14 salts reveal the charge-assisted hydrogen bond O⋯N distances to vary very little, from 2.560(2)–2.714(3) Å, with the exception of the isoquinolinium benzenesulfonate where the O⋯N distance of 2.862(7) Å is caused by additional intermolecular interactions in the solid-state.

Graphical abstract: Fluorescence enhancement of quinolines by protonation

Supplementary files

Article information

Article type
Paper
Submitted
27 May 2020
Accepted
23 Jul 2020
First published
12 Aug 2020
This article is Open Access
Creative Commons BY-NC license

RSC Adv., 2020,10, 29385-29393

Fluorescence enhancement of quinolines by protonation

E. Tervola, K. Truong, J. S. Ward, A. Priimagi and K. Rissanen, RSC Adv., 2020, 10, 29385 DOI: 10.1039/D0RA04691D

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