Kosower, Dodiuk, Kanety / N-Arylaminonaphthalenesuljonates 4179 trogen since the shape 01 the emission curves is not affected and the quantum yields of fluorescence only slightly increased in nonpolar solvents (unchanged in medium-and high-polarity solvents) by such purging. Sample temperatures were controlled a t 25.0 & 0.5 O C . Dioxane was from E. Merck, Darmstadt (spectrograde). Plots were executed with a Hewlett-Packard 98 10-9862 calculator-plotter combination.Acknowledgment. The support of the United States-Israel Binational Science Foundation (BSF) is appreciated. References and Notes(1) (a) Tel-Aviv University; (b) State University of New York, Stony Brook.(2) Previously, we numbered the Narylamino group as 2-, but we have accepted the editorial suggestion that 6is more appropriate and conforms more closely to accepted nomenclature. (IO) H. Bucherer and A. Stohmann, Chem. Zentralbl., 75, 1012 (1904); see also ref 5 and 6. (1 1) E~(30) values represent an intramolecular charge-transfer transition whereas Zvalues are based on an intermolecular charge-transfer transition. The former are therefore more suitable for the analysis of ANS emission data according to the suggestions previously made in ref 3 and 4. (24) (25)

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heights given by the V3 term, arises from the values of AH calculated for each molecule, 1110 and -46 cal/mol for the s-transgauche conversion, respectively. The relatively large AH for the ether was attributed3 to steric hindrance between the methyl tops in the gauche conformer and so it would appear that this factor is not present in the sulfide. Structural calculations on the gauche ether and sulfide indicate that the distance between the carbons of the methyl groups is 0.3 A larger in the sulfide, although the distance of 3.1 A for the sulfide is still less than twice the van der Waals radius of a -CH3 group (2 A). However, such calculations cannot be very accurate as complete structural information on these molecules is not available.The barriers to internal rotation of the methyl groups are v3o--v33 and vo3-v33 for the C-CH3 and S-CH3 torsions; they are calculated to be 1165 and 718 cm-l (3.33 and 2.05 kcal/mol), respectively. The methyl barriers of propanell and dimethyl sulfide2 were calculated previously in this laboratory to be 1147 and 679 cm-' (3.28 and 1.94 kcal/mol), respectively, which shows that the corresponding barriers in ethyl methyl sulfide are only slightly higher. The gauche S-CH3 barrier is close to that of the s-trans conformer observed by microwave spectroscopy8 (2.07 kcal/mol). These results reinforce the above con-

The emission from 1,8-naphthosultam (2H-naphth [1,8-cd]isothiazole 1,1-dioxide) (la) is composed of two bands, one for the acid (Xm" = 480 nm) and one for the corresponding anion (2, Xmal = 600 nm). The fluorescence of both la and 2, as well as that of the IV-methyl-and AT-ethyl-l,8-naphthosultams (lb and lc), has a modest sensitivity to solvent polarity. The ground-state p for la is 6.2, with pK&* of -3.0. The proton transfer rate for la to water is >5 X 1010 s_1, from the rise time of anion fluorescence by picosecond pulse techniques. The fluorescence lifetimes for la and 2 are 16 ( = 0.37, dioxane) and 1.4 ( = 0.005, H20, pH 10) ns, respectively.

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