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Item Excited Singlet and Triplet pK Values of Xanthone in Aqueous Solution(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (6), 1972) Ireland, J. F.; Wyatt, P. A. H.Xanthone, which Ikis a ground state pK of -4.1, is shown to have a pK^j) value of +0.96 by fluorescence intensity measurements and a pK(7\) of +3.0 by triplet-triplet absorption measurements. The unusual order pK(7\) >pK(5i) >pK(5’0) is also reproduced in the Forster cycle values calculated from the absorption, fluorescence, and phosphorescence maxima, though the numbers thus obtained for pK(Ti) and pKGS^) arc 2 to 3 units more positive. Forster’s Cycle applied to the triplettriplet absorption spectra of the protonated and unprotonated species indicates that pK(T2) is —0.7, so that in basic strength the second triplet state lies between So and S1.Item Quenching Effects Upon the Life-Time of Protonated 2-Naphthamide Si in Aqueous Solution(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (1), 1972) Hussain, S. Karamat; Wyatt, P. A. H.Fluorescence life-time measurements are reported for the first excited singlet of the protonated 2-naphthamide species in acid solutions in the presence of chloride, perchlorate, and sulphamate ions. Except possibly with the sulphamate anion, the quenching effect of the hydrogen ion is much greater than that of the anions in this particular case. The life-time of [graphic omitted] in the absence of quencher is 29 ns and the quenching constant for H+, 3 × 107 l. mol–1 s–1 at 25°C.