Indirect solvent assisted tautomerism in 4-substituted phthalimide 2-hydroxy-Schiff bases

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creativework.keywords2-hydroxy-Schiff bases, Crystallography, DFT, Enol/keto tautomerism, ESIPT, Phototautomerization, Phthalimides, UV–Vis spectroscopy
creativework.publisherElsevier B.V.en
dc.contributor.authorYordanov D.
dc.contributor.authorDeneva V.
dc.contributor.authorGeorgiev A.
dc.contributor.authorCrochet A.
dc.contributor.authorFromm K.M.
dc.contributor.authorAntonov L.
dc.date.accessioned2024-07-10T14:27:04Z
dc.date.accessioned2024-07-10T14:49:33Z
dc.date.available2024-07-10T14:27:04Z
dc.date.available2024-07-10T14:49:33Z
dc.date.issued2020-08-15
dc.description.abstractThe paper presents the synthesis and characterization of two 4-substituted phthalimide 2-hydroxy-Schiff bases containing salicylic (4) and 2-hydroxy-1-naphthyl (5) moieties. The structural differences of 2-hydroxyaryl substituents, resulting in different enol/keto tautomeric behaviour, depending on the solvent environment were studied by absorption UV–Vis spectroscopy. Compound 5 is characterized by a solvent-dependent tautomeric equilibrium (KT in toluene = 0.12, acetonitrile = 0.22 and MeOH = 0.63) while no tautomerism is observed in 4. Ground state theoretical DFT calculations by using continuum solvation in MeOH indicate an energy barrier between enol/keto tautomer 5.6 kcal mol−1 of 4 and 0.63 kcal mol−1 of 5, which confirms the experimentally observed impossibility of the tautomeric equilibrium in the former. The experimentally observed specific solvent effect in methanol is modeled via explicit solvation. The excited state intramolecular proton transfer (ESIPT) was investigated by steady state fluorescence spectroscopy. Both compounds show a high rate of photoconversion to keto tautomers hence keto emissions with large Stokes shifts in five alcohols (MeOH, EtOH, 1-propanol, 1-butanol, and 1-pentanol) and various aprotic solvents (toluene, dichlormethane, acetone, AcCN). According to the excited state TDDFT calculations using implicit solvation in MeOH, it was found that enol tautomers of 4 and 5 are higher in energy compared to the keto ones, which explains the origin of the experimentally observed keto form emission.
dc.identifier.doi10.1016/j.saa.2020.118416
dc.identifier.issn1386-1425
dc.identifier.scopusSCOPUS_ID:85084170687en
dc.identifier.urihttps://rlib.uctm.edu/handle/123456789/587
dc.language.isoen
dc.source.urihttps://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85084170687&origin=inward
dc.titleIndirect solvent assisted tautomerism in 4-substituted phthalimide 2-hydroxy-Schiff bases
dc.typeArticle
oaire.citation.volume237
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