title: 7-Hydroxyquinoline-8-carbaldehydes. 1. Ground- and excited-state long-range prototropic tautomerization.
abstract: Ground- and excited-state long-range prototropic tautomerization were studied for a series of 7-hydroxyquinoline-8-carbaldehydes (7-HQCs) by (1)H and (13)C NMR spectroscopy, photostationary and time-resolved UV-vis spectroscopic methods, and quantum chemical computations. These molecules represent trifunctional proton-donating/accepting systems that have been proposed to serve as models of a reversible optically driven molecular switch composed of two moieties: a molecular "frame" (7-hydroquinolines, 7-HQs) and a proton "crane" (carbaldehyde group). The NMR and electronic absorption spectra indicate a solvent-dependent equilibrium between two tautomeric forms, OH (7-quinolinol)) and NH (7(1H)-quinolinone), already in the ground state of all the compounds under study (7-hydroxy-2-methoxy-4-methylquinoline-8-carbaldehyde, HMMQC, shows only a trace of the NH form in highly polar and/or protic media). Electronic absorption and fluorescence of 7-HQCs are rationalized in terms of the ground- and excited-state hydrogen atom transfer (HAT). This process was identified by comparing the UV-vis spectroscopic properties of 7-HQCs with those of 7-HQs, synthetic precursors of the former, as well as with the characteristics of corresponding protonated cations and deprotonated anions (part 2). The experimental results are corroborated by the density functional theory (DFT) and ab initio computations, which shed some light on the differences in photophysics between variously substituted 7-HQCs.
authors.affiliation: Institute of Physical Chemistry, Polish Academy of Sciences , Kasprzaka 44/52, 01-224 Warsaw, Poland.
authors.forename: Volha
authors.initials: V
authors.lastname: Vetokhina
authors.forename: Jacek
authors.initials: J
authors.lastname: Nowacki
authors.forename: Mariusz
authors.initials: M
authors.lastname: Pietrzak
authors.forename: Michał F
authors.initials: MF
authors.lastname: Rode
authors.forename: Andrzej L
authors.initials: AL
authors.lastname: Sobolewski
authors.forename: Jacek
authors.initials: J
authors.lastname: Waluk
authors.forename: Jerzy
authors.initials: J
authors.lastname: Herbich
mesh_terms: D000447:Aldehydes / Q000737:chemistry*; D006912:Hydroxyquinolines / Q000737:chemistry*; D007536:Isomerism; D008958:Models, Molecular; D008968:Molecular Conformation; D011789:Quantum Theory; D012997:Solvents / Q000737:chemistry; D013057:Spectrum Analysis; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D000447:Aldehydes; D006912:Hydroxyquinolines; D012997:Solvents; D014867:Water