Substituent effects on excited-state acidities of some substituted 8-hydroxyquinolinium cations

Complex Formation Reactions of Scandium(ΙΙΙ), Yttrium(ΙΙΙ) and Lanthanum(ΙΙΙ) Complexes with 8−Hydroxyquinoline

“…The self-assembly of specific oligomeric complexes with certain emitting properties can be induced in approximate derivatives. Application of 8-Hydroxyquinoline derivatives to obtain new supramoleculer sensors, emitting devices or self-assembled aggregates have been described in the review of [13][14][15][16][17][18][19][20][21][22][23][24][25].…”

Photophysical Properties of 8-Hydroxyquinoline-5-sulfonic Acid as a Function of the pH: A TD-DFT Investigation

“…This phenomenon was explained in terms of a phototautomerization reaction consisting of a proton transfer from the OH function to the N atom at the excited state, to produce, from the neutral 8-HQ, the corresponding (nonemissive) zwitterion. The phototautomerization mechanism was the subject of a large number of experimental and theoretical studies. − However, there are still few data and exhaustive studies concerning the influence of the pH on the spectroscopic properties of 8-HQ (and consequently of 8-HQS). As a matter of fact, the protonation/deprotonation of the several acidic functions present in 8-HQ (or 8-HQS) could significantly alter the spectral properties of this molecule at the ground (absorption) and the excited (emission) state.…”

“…To gain insights on the excited state properties of 8-HQS, the accurate knowledge of excited state acidic dissociation constants (p K a *) plays a crucial role. Experimentally, in the case of 8-HQ derivatives, methods based either on fluorimetric titration , or on the Föster cycle were applied. Indeed, the first supposes the existence, at the excited state, of the equilibrium between each acid and corresponding basic form, which is not a priori granted for 8-HQ, while the latter involves drastic simplifications (such as the assumption of a constant vibrational contribution at the ground and excited state).…”

“…The phototautomerization mechanism was the subject of a large number of experimental and theoretical studies. [11][12][13][14][15] However, there are still few data and exhaustive studies concerning the influence of the pH on the spectroscopic properties of 8-HQ (and consequently of 8-HQS). As a matter of fact, the protonation/ deprotonation of the several acidic functions present in 8-HQ (or 8-HQS) could significantly alter the spectral properties of this molecule at the ground (absorption) and the excited (emission) state.…”

“…20 To clarify this situation, we recently computed (applying two different computational protocols) the ground state pK a 's of 8-HQS. 12 The results obtained unambiguously showed that the fully protonated and cationic species (8-HQS-C, Figure 1) does not exist in aqueous solution (that is in the pH range [1][2][3][4][5][6][7][8][9][10][11][12][13][14] and that the zwitterionic form (8-HQS-Z, Figure 1) is only present at medium pH and in very low concentration.…”