band of 1-CNC as the temperature increases. ConclusionsIntramolecular hydrogen bonding between the N-H bond and the carbonyl group in 1-COOEC as well as the intermolecular double hydrogen bonding of the N-H-N=Ctype between molecules of 1-CNC in CC14 solutions have been investigated by infrared spectroscopy.A distance of about 2.1 Á between the N-H proton and the C=0 group favors the occurrence of intramolecular hydrogen bonding in 1-COOEC. Nevertheless, the rotation of the carboethoxy group around the Car-C bond causes this compound to exist in two configurations: the free N-H and the hydrogen-bonded N-H. These two configurations manifest themselves by the two well-separated bands in the N-H stretching frequency range of the infrared spectrum. From the temperature dependence of the intensities of these bands the intramolecular association constant K = 1.33 ± 0.26 at 25 °C, the enthalpy change AH0 = -7.40 ± 0.22 kJ mol"1, and the entropy change AS°= -22.6 ± 1.4 J mol"1 K"1 have been calculated for the intramolecular hydrogen bonding in 1-COOEC.1-CNC in nonpolar solvent is undergoing hydrogen-bonding self-association. The infrared spectrum of 1-CNC in carbon tetrachloride possesses two bands which have been well characterized as N-H band of the monomer and the double N-H band of the cyclic dimer. The relative intensities of these bands change with the concentration of 1-CNC. Moreover, the intensity of the N-H (dimer) band strongly depends on the variation of the temperature. The equilibrium constant of the dimer formation of 1-CNC in CC14 at 25 °C has been obtained as 92 ± 16 mol"1 dm3 4. The enthalpy change and the entropy change for the complexation of 1-CNC in CC14 are -33.3 ± 2.8 kJ mol"1 and -74 ± 10 J mol"1 K"1, respectively. These results are in good agreement with the cyclic structure of the dimer discussed.Acknowledgment. The authors thank the Natural Sciences and Engineering Research Council of Canada and the "Ministére de 1'Education du Quebec" for financial assistance. Thanks are also due to Mr. Jean-Claude Bolduc for having taken many of the infrared spectra on the FTIR apparatus.Registry No. l-(Carboethoxy)carbazole, 56995-05-2; 1-cyanocarbazole, 83415-88-7.

The nature of the excitation-dependent luminescence of p-7V,7V-dimethylnitroaniline (DMNA) is examined. The results indicate that the anomalous luminescence behavior of DMNA is due to subtle differences in the molecular environment rather than a characteristic of the isolated molecule. The luminescent properties are ascribed to different H-bonded or rotameric forms, their energy levels being significantly determined by the local solvent polarity.

densities determined from the proton hyperfine interactions, one calculates for the isotropic 13C hyperfine interaction a value, ac(odd) = 1.64 G. This compares favorably with the experimental value of 1.57 G which is calculated from the trace of the I3C tensor elements (Azz = +2.5 G, A,, = A, = +1.1 G). In like manner, one obtains a,(even) = -0.67 G, which compares well with the experimental value of -0.56 G calculated from the 13C tensor elements A,, = -0.75 G and A,, = A, = -0.46 G.The preceding results leave little doubt as to the correctness of the assignment of signs for the elements of the hyperfine tensors determined from ENDOR and TRIPLE measurements. Moreover, these results further support the determination of spin density values of p,(odd) = +0.06 and pc(even) = -0.02 which were initially defined from analysis of the isotropic and anisotropic parts of the proton hyperfine interactions. Finally, the results of the present calculations illustrate the similarity of v u on-site Coulomb interactions in polyacetylene and in small organic radicals and suggest that the magnitudes of the interaction integrals do not change drastically with length of the polyene. Acknowledgment.The technique of total luminescence spectroscopy is used in the analysis of the excitation-dependent phosphorescence of phenazine in ethanol at 77 K. The excitation dependence is due to three different phenazine species in the protic medium: free molecules, molecules with one H bond to either ethanol or water, and molecules forming two H bonds, at least one of which is to water.

excitation profile in the Soret region (433-436 nm). These origins are consistent with the electronic structure of a species having at least three close-lying electronic levels. A more substantial assignment of the species and chemical bonding discussed in this work awaits the outcome of the resonance Raman studies of the intensity of normal modes in the ground state, specifically of the carbonyl vibrational modes. Concluding RemarksIn this article, it has been shown that wavelength-dependent and time-resolved fluorescence spectroscopy of Chi a in hexane can be used to study the presence of various complexes including aggregated species. These results indicate the extreme usefulness of fluorescence techniques in areas where absorption spectroscopy techniques fail to discriminate between the properties of various species. The fluorescence spectra reveal mono-and dihydrated monomeric Chi a species in highly dilute hexane solutions while the monohydrated complex is also present in solutions of higher concentration. At higher concentrations evidence from fluorescence data has indicated the presence of a donor/acceptor type dimer as well as other aggregated species. The exact structure of these latter species is not known, but this species has interesting properties as observed from the resonance Raman excitation profile.

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