The absolute fluorescence quantum yield of 9,10-diphenylanthracene in deaerated cyclohexane, the value of which has long been a matter of controversy, has been determined by use of a new method based on chemical actinometry. This technique avoids many of the intrinsic error sources of the other absolute methods. The sample's emission intensity is measured by almost completely surrounding the sample with an actinometer solution, and the excitation intensity is directly measured with the same type of actinometer. The measured sample emission intensity is corrected for the fraction of exciting light which is not absorbed within the sample solution and the fraction of fluorescence which escapes through the entrance and exit ports of the excitation beam. The absolute fluorescence yield is the ratio of the "corrected" sample intensity to the excitation intensity. The value we obtain with this method for 9,10-diphenylanthracene in cyclohexane is 0.90 to within 4%.completely with an actinometer solution, measures the (1)

Inclusion compounds in the systems naphthalene–β-cyclodextrin (CDx) and 2-methoxynaphthalene (MN)–o-dicyanobenzene (DB)–β-cyclodextrin in aqueous solution were studied by means of absorption and fluorescence spectra. In the former system a naphthalene excimer fluorescence was observed. By the analyses of the concentration dependence of the absorption spectra and the excimer fluorescence intensities, the species responsible for the excimer fluorescence is identified as a 2:2 inclusion compound which is formed by association of two 1:1 naphthalene–CDx inclusion compounds, not a 2:1 inclusion compound in which two naphthalene molecules enter into the cavity of one CDx molecule. In the latter system, absorption and fluorescence spectra due to a charge transfer complex of MN with DB were observed. By analyses similar to the naphthalene case, the existence of a 1:1:2 association compound formed between a MN–CDx inclusion compound and a DB–CDx inclusion compound is confirmed. Fluorescence quenching by I− and IO3− was also studied for the inclusion compounds in both systems.

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From the pH dependence of pyrene (Py) excimer fluorescence in -cyclodextrin ( -CD) solutions, the Py excimer fluorescence is concluded to be entirely due to a 2:2 inclusion compound of -CD with Py. In a Py solution containing neutral -CD, there are, in addition to the 2:2 inclusion compound, 1:1 and 1:2 Py~7-CD inclusion compounds that emit only Py monomer fluorescence. From a simulation of the Py excimer fluorescence intensities as a function of -CD concentration, equilibrium constants for the formation of these inclusion compounds have been estimated. Anionicand /3-CD have been found to form 1:1 inclusion compounds with Py. The equilibrium constant for the formation of the 1:1 inclusion compound with anionic -CD is less than that with neutral -CD. In contrast, the equilibrium constant for anionic ¡8-CD is greater than that for neutral /3-CD. A conformational change in theor /3-CD cavity is the most probable explanation for these findings: The diameter at the wider end of theor /3-CD cavity may be expanded by the electrostatic repulsion between negative charges on oxygen atoms of secondary hydroxyl groups that are rimmed on the wider end of the cavity. When Py is incorporated into the cavities of anionic CDs, Py experiences a rather polar environment in spite of the enclosing of Py by the hydrophobic interior surface of CDs.

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