Acid–base strength and acido(fluoro)chromism of three push–pull derivatives of 2,6-distyrylpyridine
| Autor: | Letizia Mencaroni, Alessio Cesaretti, Fausto Elisei, Irena Škorić, Milena Mlakić, Anna Spalletti |
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| Rok vydání: | 2022 |
| Předmět: |
Acid–base properties
acid-base properties acido(fluoro)chromism push-pull systems 2 6-distyrylpyridine derivatives spectroscopic titrations Förster cycle Acid–base properties Acido(fluoro)chromism Push–pull systems 2 6-Distyrylpyridine derivatives Spectroscopic titrations Förster cycle Acido(fluoro)chromism Push–pull systems Spectroscopic titrations Physical and Theoretical Chemistry 6-Distyrylpyridine derivatives Förster cycle |
| Zdroj: | Photochemical & Photobiological Sciences. 21:935-947 |
| ISSN: | 1474-9092 |
| Popis: | The acidochromism and acid–base properties of 2,6-distyrylpyridine (2,6-DStP) derivatives bearing on the sides push/pull substituents (namely two dimethylamino, one nitro, and one methoxy and two nitro groups in the case of 2,6-bis[(E)-2-(4-dimetylaminophenyl)ethenyl]pyridine, 2-[(E)-2-(4-nitrophenyl)ethenyl],6-[(E)-2′-(4′-methoxyphenyl)ethenyl]pyridine and 2,6-bis[(E)-2-(4-nitrophenyl)ethenyl]pyridine, respectively) were investigated by stationary and time-resolved spectroscopies. The sensitivity of the absorption and emission spectrum to the medium acidity was found to enhance in the dimethylamino-derivative relative to the unsubstituted 2,6-DStP, also because of the second protonation by the N(CH3)2 group. Spectrophotometric titrations, also processed by a global fitting approach, gave pKa values, for the protonation of the central pyridine, higher in the derivatives with electron-donor unities and lower in compounds bearing electron-acceptor groups. A fluorometric titration was performed in the case of the dimethylamino-derivative thanks to non-negligible emission efficiencies for both neutral and protonated species, unveiling an attractive naked-eye acido(fluoro)chromism from green to yellow upon pyridine protonation, and then to purple with the second protonation involving the lateral N(CH3)2 substituent. Due to the extremely short excited-state lifetimes, as resulted from femtosecond transient absorption experiments, the pKa values for the excited state (pKa*) were estimated through the Förster cycle, revealing that the monoprotonated species of the dimethylamino-derivative would become upon excitation the only stable form in a wide range of pH. Graphical abstract |
| Databáze: | OpenAIRE |
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