Schäfer, KatyIhmels, HeikoBohne, CorneliaPapera Valente, KarolinaGranzhan, Anton2017-07-1820162016Schafer, K. et al., (2016). Hydroxybenzo[b]quinolizinium Ions: Water-Soluble and Solvatochromic Photoacids. The Journal of Organic Chemistry, 81, 10942-10954. doi: 10.1021/acs.joc.6b0199http://dx.doi.org/10.1021/acs.joc.6b01991http://hdl.handle.net/1828/8352It 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.enArticle