Complexation effect of γ-cyclodextrin on a hydroxyflavone derivative: Formation of excluded and included anions

Proton and charge transfer reactions dynamics of a hydroxyflavone derivative in a polar solvent and in a cyclodextrin nanocavity

“…formation of A, as it has been reported for its parent molecule 3HF [25]. In presence of c-CD the global emission intensity increases, and the shape of the spectrum changes due to the emission of the A form (550 nm) [27]. Two kinds of complexes are formed: one in which the chromone moiety is inside the cavity (inclusion complex), and the other one has the A structure of DMAF outside of the cavity (capped complex) (Scheme 1b).…”

“…Excitation of DMAF in DMF at 393 nm shows two fluorescence bands with maxima at around 520 nm (emission of ICT form) and 580 nm (emission of Z). A small portion of anionic form emits at $550 nm [27].…”

“…The decrease in the intensity of the enol form (E, maximum at 400 nm) absorption band and the formation of a new band corresponding to the anionic form (A, centred around 475 nm) in presence of c-CD, were explained in terms of the formation of strong H-bond interactions of E with the nanocavity [27]. This interaction leads to the …”

“…3-hydroxyflavone (3HF) and its derivatives, and among them 4 0 -dialkylaminoflavonols, have shown remarkable solvent effect (mainly due to the polarity) on the excited-state reactions [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Their fluorescence spectra mainly exhibit two bands.…”

“…Here, and for simplicity, we will refer to the latter structure as Z. In polar solvents, the intramolecular proton-transfer (IPT) process is reversible [27]. Upon increasing the solvent polarity, the equilibrium shifts toward the ICT state possessing a large dipole moment with respect to the T structure [19,23].…”