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The effect of coinclusion of alcohol (ROH) on the stoichiometry, stability, spectral, as well as photophysical properties of β-cyclodextrin (β-CD) complexes of 4H-1-benzopyran-4-thione (BPT) was studied. Although the binary complex was of 1:1 stoichiometry, the formation of ternary complexes of 1:2:2 BPT:ROH:β-CD stoichiometry was observed. The formation of the ternary complexes is revealed by a dramatic enhancement of fluorescence from the second excited singlet state and phosphorescence occurring from the two lowest thermally equilibrated triplet states. The increase in intensities of these emissions is discussed in terms of shielding the emissive molecule from bulk water molecules and expulsion (perhaps still partial) of water molecules coincluded with the BPT molecule in the binary complex. Even the coinclusion with a molecule that acts in solution as a very efficient quencher of BPT phosphorescence led to a very strong phosphorescence enhancement, which indicates that there is a spatial separation of reactive centers of the two coincluded molecules. The possible reasons for the changes in the shape in the phosphorescence spectrum and the appearance of vibrational structure in the S2 band in the absorption spectrum are also discussed. The stability constants of the ternary complexes determined from absorption, fluorescence, and phosphorescence measurements depended strongly on the molecular size and structure of a coincluded alcohol.

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A procedure for determination of reactivity of primary, secondary, and tertiary C−H bonds in molecules of saturated hydrocarbons has been proposed. The procedure involves measurements of picosecond lifetimes of xanthione in the S2 state (τS2) from the fluorescence decay (by the TCSPC method) in selected hydrocarbons as solvents. On the basis of the lifetimes measured, the rate constants of hydrogen abstraction, (k H), are determined for hydrocarbons having only primary C−H bonds, primary and secondary C−H bonds, and primary and tertiary C−H bonds. The obtained highly accurate k H values show significant differences and are k H = 1.4 × 1010 s-1, 5 × 1010 s-1 and 20 × 1010 s-1, for the primary, secondary, and tertiary bonds. The values of k H determined by the procedure proposed can be used to assess the relative energy of C−H bonds and to infer about the presence of steric hindrance for the reactive tertiary C−H bonds. They can also be of interest in the studies of primary photochemical processes in hydrocarbon solvents and in the proper choice of solvents for photophysical and photochemical studies.

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THERE ARE but a few papers on the photochemical properties of the isopropyl alcoholhydrogen peroxide system and they give little information on the products arising in this system. Some papers report qualitative studies [l], whereas others are only incidentally concerned with the quantum yield of hydrogen peroxide decomposition in the presence of isopropyl alcohol and perchloric acid [2] or the identification of free radicals by the EPR method [3,4].Photooxidation of liquid isopropyl alcohol by oxygen in the presence of certain inorganic and organic catalysts of the semiconductor type has been studied by Komuro [5] and others [6,7]. Acetone, hydrogen peroxide and pinacol, were found as photoproducts and the authors proposed a free-radical mechanism for their formation.The present study was aimed at determining, qualitatively and quantitatively, some products of photolysis arising in a mixture of isopropyl alcohol and hydrogen peroxide in the presence of air. The quantum yields of these products and the decrease of substrate were determined, and the mechanism leading to formation of the identified compounds is discussed. EXPERIMENTALThe isopropyl alcohol used was of "AnalaR" grade. It was dehydrated over barium oxide and subjected to fractionation in a highly efficient fractionating column. Fractions in the 81 -5-82.5"C range were collected.Hydrogen peroxide 30 per cent of "AnalaR" grade without stabilizers was diluted with twice-distilled water to the required concentration.Samples of the mixture of 2.5 M isopropyl alcohol and 2-5 M hydrogen peroxide, of 80ml volume, were placed in a cylindrical quartz vessel provided with a water jacket, into which the light source was introduced.Irradiation was performed using a 7 W Original-Hanau N K 6/20 type low pressure mercury lamp yielding almost monochromatic light of 2537 A. The whole equipment