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The 4\u2010pyridyl substituted rosamine was further converted into the <jats:italic>N<\/jats:italic>\u2010methylpyridinium derivative through <jats:italic>N<\/jats:italic>\u2010alkylation using methyl iodide. The influence of the position and cationization of the nitrogen atom of the pyridyl ring in the physicochemical properties of fluorophores was investigated by <jats:sup>1<\/jats:sup>H, <jats:sup>13<\/jats:sup>C, <jats:sup>15<\/jats:sup>N\u2005NMR spectral analysis, UV\/Vis and fluorescence spectroscopy, single\u2010crystal X\u2010ray diffraction (4\u2010pyridyl and <jats:italic>N<\/jats:italic>\u2010methylpyridinium derivatives) and thermal\u2010behavior analysis. Curiously, for ethanolic solutions of 4\u2010pyridyl and <jats:italic>N<\/jats:italic>\u2010methylpyridinium derivatives an extinction of color and fluorescence over time was observed. This phenomenon was further studied and the data revealed that it is the result of nucleophilic addition of ethoxide ion to the central 9\u2010position of the xanthene. The kinetics of the process is slower for the 4\u2010pyridyl rosamine, which emphasizes the importance of the charge in the <jats:italic>N<\/jats:italic>\u2010methylpyridinium analogue in the reactivity of the molecule towards a nucleophile agent. This phenomenon is reversible, meaning that the compounds can be rapidly recovered by decreasing the pH, opening new avenues in the sensing applications of this class of rosamines.<\/jats:p>","DOI":"10.1002\/chem.201903313","type":"journal-article","created":{"date-parts":[[2019,8,4]],"date-time":"2019-08-04T21:44:50Z","timestamp":1564955090000},"page":"15073-15082","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":10,"title":["Synthesis of Pyridyl and <i>N<\/i>\u2010Methylpyridinium Analogues of Rosamines: Relevance of Solvent and Charge on Their Photophysical Properties"],"prefix":"10.1002","volume":"25","author":[{"given":"Andreia","family":"Leite","sequence":"first","affiliation":[{"name":"LAQV\/REQUIMTE Departamento de Qu\u00edmica e Bioqu\u00edmica, Faculdade de Ci\u00eancias da Universidade do Porto  4169-007 Porto Portugal"}]},{"given":"Lu\u00eds","family":"Cunha\u2010Silva","sequence":"additional","affiliation":[{"name":"LAQV\/REQUIMTE Departamento de Qu\u00edmica e Bioqu\u00edmica, Faculdade de Ci\u00eancias da Universidade do Porto  4169-007 Porto Portugal"}]},{"given":"Daniel","family":"Silva","sequence":"additional","affiliation":[{"name":"LAQV\/REQUIMTE Departamento de Qu\u00edmica e Bioqu\u00edmica, Faculdade de Ci\u00eancias da Universidade do Porto  4169-007 Porto Portugal"}]},{"given":"Ana I. 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