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Hydroxybenzo[b]quinolizinium Ions: Water-Soluble and Solvatochromic Photoacids

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journal contribution
posted on 18.10.2016 by Katy Schäfer, Heiko Ihmels, Cornelia Bohne, Karolina Papera Valente, Anton Granzhan
It is shown by photometric and fluorimetric analysis, along with supporting theoretical calculations, that hydroxy-substituted benzo­[b]­quinolizinium derivatives display the characteristic features of organic photoacids. Specifically, the experimental and theoretical results confirm the strong acidity of these compounds in the excited state (pKa* < 0). The combination of the prototropic properties of 8- and 9-hydroxybenzo­[b]­quinolizinium with the particular solvent–solute interactions of the excited acid and its conjugate base leads to a pronounced fluorosolvatochromism, hence the emission maxima shift from 468 nm (8-hydroxybenzo­[b]­quinolizinium) or 460 nm (9-hydroxybenzo­[b]­quinolizinium) in CH3CN to 507 and 553 nm in DMF, respectively. This novel type of photoacid represents several features that may be used for applications as water-soluble fluorescent probes or as a source for the photoinduced supply of acidity.